Frequently Asked Questions List for comp.periphs.scsi
Current Editor: Gary Field (gfield@zk3.dec.com)
(Where you see reference to [Editor(GF)] that means me.)
Last updated: January 28, 1999
Note: Please allow the whole file to load before clicking on any links. If you click on a link before the portion of the page it points to has loaded, you just get sent to the top of the document.
Acknowledgements
Thanks to David Sanderson for helping me improve the quality and compatability
of the HTML in this document.
A Word From the Editor
I am continually asked "Why should I buy SCSI drives instead of EIDE?"
I hope this will summarize my thoughts on that issue:
For someone to who doesn't need a real multi-tasking workstation or server, the only reason for paying the extra money for SCSI is flexibility. EIDE/ATA is strictly for "inside the case" peripherals. SCSI allows you to attach a large collection of add-ons like scanners, CD recorders, tape drives (or even devices not conceived of yet), either inside or outside the CPU case in whatever manner suits your needs or wishes.
If you like non-technical analogies:
SCSI is like a palace, with an architecture that was well thought out from the beginning and built upon over a period of time to make it even greater than originally envisioned.
IDE/ATA is like a log cabin, with a dirt floor, built from whatever was found lying around in late fall just before the snow came. It can't be expanded because it has no foundation and would collapse under its own weight.
Both provide shelter. SCSI costs more (but not as much as a palace :-)).
Take your pick.
If automobile analogies are more to your liking:
A Ford Escort will get you to work just as fast as a Volvo station wagon. Which would you rather go on vacation in? Which would you rather be in if an accident occurs?
If your computer is nothing more than a machine that's only purpose is to perform a certain set of tasks, and you don't expect to want any more out of it, IDE is probably for you.
On the other hand, if you enjoy computing and are always looking for more things your computer can do for you, SCSI will help enhance the experience for you. You won't regret the investment.
Just as with a palace however, you need to learn your way around. That's where this FAQ comes in!
FAQ history: Created by Johnathan Vail (vail@prepress.pps.com) from articles submitted to him by comp.periph.scsi readers.
Maintained by Johnathan Vail until November 1993.
Where to get the latest copy of this FAQ:
Pointers to the comp.periphs.scsi FAQ are posted to Usenet during the first week of each month.
via World Wide Web (WWW):
Attention SCSI vendors: There are a few articles in this FAQ where vendor contact information, and in a few cases, part numbers, are listed. This is not an attempt to steer business to any particular vendor but only to provide possible sources of certain "hard to find" SCSI accessories (particularly special cables, adapters and terminators). If you want to be listed in one or more articles please send your contact info and which items you can provide to the FAQ editor.
I will not include pointers for devices like hard disks, tapes, CDROMs etc., which I consider readily available.
Categories:
SCSI Performance Determination and Enhancement:
SCSI Manufacturer Contact Information:
How can I contact:
Manufacturer Specific Questions:
Device Model Specific Questions:
Answers to the Questions:
QUESTION: What is SCSI?
ANSWER From: LSD, L.J.Sak@Kub. Edited by Gary Field (gfield@zk3.dec.com)
SCSI2 is the most recent version of the SCSI command specification and allows for scanners, hard disk drives, CD-ROM players, tapes [and many other devices] to connect.
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QUESTION: What information should
I provide when asking a question in the comp.periphs.scsi newsgroup?
ANSWER From: Gary Field (gfield@zk3.dec.com)
If you don't know what some of these things mean, read the rest of this document until you do. You'll get much more help if you appear to have made an effort to find the answer on your own before asking for help.
Asking a question like "My scanner doesn't work, how come?" may not even get you a response.
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QUESTION: What do all these SCSI
buzzwords mean?
ANSWER From: hennes@stack.urc.tue.nl (Hennes Passmann)[Editor(GF)]
I/O, Req, C/D, Sel, Msg, Rst, Ack, Bsy, Atn, DB(p), DB(7) ... DB(0).
ANSWER From: hennes@stack.urc.tue.nl (Hennes Passmann)
1998
ANSWER From: Gary Field (gfield@zk3.dec.com)
In reality, there is no practical reason to do this. Any SASI device is so obsolete that is has no real value in a system being used in 1990 or later.
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QUESTION: How should I lay out
my SCSI bus? What should I avoid?
QUESTION: Where do I put the terminators?
QUESTION: Where should the adapter card be placed?
Answers From: Nick Kralevich <nickkral@cory.eecs.berkeley.edu>
edited by Gary Field (gfield@zk3.dec.com)
The SCSI bus MUST run continuously from one device to another, like this:
DEVICE A --------- DEVICE B --------- DEVICE C -------- DEVICE D
Where device A, B, C, and D can either be internal or external devices.
The devices on the SCSI bus should have at least 4 to 6 inches of cable between devices. This is to satisfy the SCSI-2 requirement that "stubs" be placed at least .1 meters apart. Some devices that have a lot of internal wiring between the connector and the SCSI chip can look like a "stub" or bus discontinuity. The reason for all these requirements is that a SCSI bus is really 18 "transmission lines" in the wave theory sense. A pulse propagating along it will "reflect" from any part of the transmission line that is different from the rest of it. These relections add and subtract in odd combinations and cause the original pulse to be distorted and corrupted. The terminators "absorb" the energy from the pulses and prevent relections from the ends of the bus. They do this because they (hopefully) have the same impedance as the rest of the transmission line.
The SCSI bus must not have any "Y" shape cabling. For example, setting up a cable that looks like this is NOT allowed:
DEVICE B \ \ \ >------------- DEVICE C ----------- DEVICE D / / / DEVICE A Where do I put the terminators?Termination must be present at two and ONLY two positions on the SCSI bus, at the beginning of the SCSI bus, and at the end of the SCSI bus. There MUST be no more than two, and no less than two, terminators on the bus.
Termination must occur within 4 inches (.1 meter) of the ends of the SCSI bus.
The following ARE acceptable: +------------+----------+-----------+-----------+---------+ | | | | | | DEVICE A Unconnected Unconnected DEVICE B DEVICE C Adapter Terminated Terminated +------------+----------+-----------+-----------+---------+ | | | | | | DEVICE A Unconnected DEVICE B Unconnected Adapter DEVICE C Terminated Terminated +------------+----------+-----------+-----------+---------+ | | | | | | Adapter DEVICE A DEVICE B Unconnected Unconnected DEVICE C Terminated Terminated The following ARE NOT allowed: +------------+----------+-----------+-------------------+ | | | | | DEVICE A DEVICE B Adapter Unconnected Unconnected Terminated Terminated +------------+----------+-----------+-----------+ | | | | | Termination DEVICE A DEVICE B DEVICE C Adapter Terminated
The placement of the SCSI adapter card can be on the end, at the beginning, or somewhere in the middle of the SCSI bus.
Quite frankly, placement of the controller card isn't special.
The adapter card is just another device on the SCSI bus.
As long as the rules above and in other sections of this FAQ are followed, there should be no problem placing the adapter card anywhere on the SCSI bus.
However, if you place the adapter card somewhere in the middle of the SCSI bus, you must be sure to disable termination on the adapter card. As noted previously, a SCSI device is only allowed to have termination if it's at the end of the bus. Only two terminators are allowed to terminate the SCSI bus, one at each end.
One last note: It doesn't make any difference where each SCSI ID is placed along the bus. It only matters that no two devices have the same ID. Don't forget that the adapter has an ID too. (Usually ID 7).
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QUESTION: What is a SCSI terminator?
Why do I need them?
ANSWER From: Gary Field (gfield@zk3.dec.com)
A SCSI bus is a transmission line. To prevent reflections from the ends of the bus, you need a device which makes the transmission line appear to be of infinite length. This is done by attaching resistors which have the same resistance as the characteristic impedance of the transmission line to the ends of the bus. Also, since SCSI line drivers are open-collector (which can only pull a signal low), a pull-up resistor is needed to pull the signal high when it's not asserted.
If the ends of the bus are not terminated, the signal pulses will reflect off these open ends and travel back along the bus in the other direction. The resulting adding and cancelling of signal amplitudes distorts and corrupts the SCSI signals.
There are two basic types of terminators, active and passive. Passive terminators were considered adequate in SCSI-1 when the bus only ran at 5 MHz, but with 10 MHz and faster bus speeds active terminators are required.
The active terminators both terminate the bus better (less reflection) and supply cleaner pullup current (due to their Voltage regulation).
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QUESTION: Is the spacing of connectors
on a SCSI cable important?
ANSWER From: Gary Field (gfield@zk3.dec.com)
The ANSI SCSI spec's say that "stubs" on a SCSI bus must not be any more than .1 meters (4 in.) long. In the most recent spec's there are also guidelines that say you shouldn't place "stubs" any closer than .3 meters (12 in.) apart. Since each device attached acts as a "stub", you really shouldn't place connectors any closer than this. This gets to be more important as your bus performance goes up. i.e. with Fast20 it is very important, but with SCSI-1 it doesn't really matter much. Since Fast20 also limits your overall bus length to 1.5 meters (for single ended) this also means you shouldn't really connect more than 5 devices for best reliability.
Another minor enhancement involves altering the spacing of adjacent connectors to prevent reflection resonance.
e.g. place connectors at one end, then .3m, then .56m then .86m then 1.12m
Overall, the cable impedance and configuration (straight vs. twisted pair) are probably more significant factors than connector spacing. However, if there is room for the extra cable, I recommend spacing the connectors as described above for best reliability.
Excess cable length is also a bad thing, so basically all these factors must traded off against each other to build the best SCSI cable for a given situation.
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QUESTION: How long can my SCSI
bus be?
ANSWER From: Gary Field (gfield@zk3.dec.com)
The SCSI length limits are based on the speed of the fastest device attached to the bus.
Here's a table which shows the limits:
Speed of FASTEST device |
Max. single-ended bus length |
Max. HV Diff. bus len. |
Max. LVD bus length |
5 MHz (SCSI1 synch.) |
6 meters |
25 meters |
12 meters |
10 MHz (SCSI2 FAST) |
3 meters (not recommended) |
25 meters |
12 meters |
20 MHz (Ultra or Fast20) |
1.5 meters (not recommended) |
12 meters (not specified) |
12 meters |
40 MHz (Ultra2 or Fast40) |
Not recommended |
Not specified |
12 meters |
These limits assume the use of good quality cable, which maintains its characteristic impedance between 90 and 130 Ohms and the use of active terminators at each end of the bus.
Notice that I used the term MHz to specify speed since MB/sec. changes with the bus width.
Note: Bus width doesn't change the maximum allowable length. The bus width is independent of bus length or speed.
The above table assumes that you know the max. speed of your devices (usually by looking in the manuals). Some software (like Adaptec EZ-SCSI) provides a driver status monitor which will tell you what mode the devices are actually in. This is important, since any synchronous speed must be negotiated by either the device, or the adapter. The speed actually used will be the least common denominator between the two.
For example, if a Fast20 disk is attached to a 'SCSI2" host adapter that only goes up to Fast10, the device will only run at 10 MHz.
In systems with high performance disks and external peripherals which require long cables (i.e. external scanners, tapes or CDROM changers), you may want to put the external devices on their own bus to avoid slowing down the fast disks. There are dual channel host adapters to make this simpler (avoids using multiple IRQs etc).
ANSWER From: Gary Field (gfield@zk3.dec.com)
Pros of IDE/ATA:
Now that I've said that, here's an article to show that there's more than one opinion on this subject:
From: Ed Schernau <mithrandir@ids.net>
Subject: FYI: EIDE and DMA/Scatter-Gather
The Western Digital Caviar EIDE drive that came in what is now the file server in our office came with a Win3.x 32 BDA driver which allowed the user to select DMA type (B or F) and to implement scatter-gather.
Also, the Intel Triton chipset implements 2 EIDE controllers, and I know that at least the 1 on the PCI bus supports bus-mastering, as well as DMA. However, PIO transfers can be faster, the infamous Mode 4 can in theory, do 16.6 MB/sec and I've heard of a Mode 5 which can do 22 MB/sec. Which [PIO] is only a benefit in single-tasking systems like DOS or Win3.x. Sounds like Intel is trying to make EIDE into SCSI, eh?
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QUESTION:Should I spend the extra money
on SCSI or just get IDE?
ANSWER From: Andrew Korn (korn@eik.bme.hu)
For home users this is a difficult question to answer in general. It totally depends on how you use your system, what operating systems are installed, and whether you will add more I/O devices in the future.
For server systems in a corporate environment the only sensible answer is to go with SCSI peripherals.
IDE has been improved a lot in the past few years, so in most cases it will be an acceptable choice for home users. You should consider the following
(we are mostly talking PC hardware from now on):
1. Your motherboard probably has an integrated EIDE controller capable of supporting up to four devices. (Older motherboards may not have a dual-channel IDE controller, in which case only two drives can be connected; even older motherboards may not be equipped with an IDE controller at all.) If not, an IDE controller for your system should cost less than $30, which is about half of what a decent SCSI host adapter (Symbios 53C810 based) would cost you. On the other hand, some high-end motherboards come with integrated SCSI host adapters.
2. EIDE is a single threaded architecture. This means that of the two drives connected to an IDE channel, one will always be idle while the other is executing a command. If you only want a hard disk and a CD-ROM drive, you can install the CD-ROM on the secondary IDE channel (the hard disk will probably be the primary 'master' drive); in this case, the aforementioned limitation does not affect you. Also, if you only plan on using single-tasking operating systems such as DOS, you needn't be concerned about this single-threadedness.
SCSI devices share the bus bandwidth efficiently by allowing one device to transfer data while another is seeking or rewinding its media. This will, however, only gain you performance if you use a proper multi-tasking operating system (such as Linux [Editor(GF): or Windows NT]).
3. By default, IDE devices use PIO (Programmed I/O) to communicate with the rest of the system. This has the drawback of consuming a lot of CPU time. However, most newer EIDE controllers support bus-mastering and most drives support DMA or even UDMA transfer modes. Using bus-master DMA decreases CPU consumption to almost zero. (It may not be easy to activate the DMA transfer mode under DOS, however.)
Early SCSI host adapters had much the same problem, but all newer ones support DMA transfers.
4. If you plan to use only two drives (one per IDE channel), IDE will probably be slightly faster and definitely less expensive than SCSI.
If you think you need more than two drives, plan to use a multi-tasking environment (such as Unix, OS/2, Netware or Windows 95/NT), and think that performance is more important than cost, SCSI is the way to go.
Anything bigger than a small low-cost Linux-based server should probably use SCSI.
5. IDE tapes are not as cool as SCSI tapes. They tend to be slower, less reliable and less compatible with each other than SCSI tape drives. SCSI tapes are more expensive, however.
6. IDE is probably slightly easier to install. Termination is not an issue, and it will probably require no effort on your part to make the system aware of any new devices you add. In some increasingly rare cases this may not be true for SCSI. (You know what SCSI stands for? "System Can't See It." :))
Especially with older systems it may not be trivial (or, in rare cases, even possible) to make the computer boot from a SCSI drive.
7. It is problematic to add more than four IDE drives to a system. If you think you will need more than that, SCSI is probably the choice for you.
If your motherboard came with an integrated EIDE controller, however, there is no need to ignore that feature; you can have a mixed system with both IDE and SCSI devices. (Remember to buy SCSI where performance and parallelism is an issue; but there is no need to buy an expensive SCSI CD-ROM drive if an IDE drive would suit your needs.)
8. If you need high reliability, you want to buy a RAID capable SCSI host adapter. Be aware, however, that it is possible to emulate RAID from software; Linux can do RAID 0, 1, 4 and 5 with any mixture of SCSI and IDE disks. This software-based solution is probably less reliable and slower than a true RAID controller, but certainly also much less expensive.
[Editor(GF): ATA and IDE are basically the same thing, and the terms are used interchangably in this document.]
Here's a discussion that shows some of the advantages of SCSI in more detail:
from: Greg Smith (GREGS@lss-chq.mhs.compuserve.com)
Under DOS (and DOS/win3.1), there is very little useful work the host can do while waiting for a disk operation to complete. So handing off some work from a 66 MHz 486 to, say, an 8 MHz Z80 (on the controller) does result in a performance loss. Under EVERY other OS worth discussing (Unix, Netware, NT, OS/2, Win95 etc) the processor can go off and do something else while the access is in progress, so the work done by the other CPU can result in a performance increase. In such systems, due to virtual memory, a 64K byte 'contiguous' read requested by a process may be spread to 16 separate physical pages. A good SCSI controller, given a single request, can perform this 'scatter/gather' operation autonomously. ATA requires significant interrupt service overhead from the host to handle this.
Another big issue: ATA does not allow more than one I/O request to be outstanding on a single cable, even to different drives. SCSI allows multiple I/O requests to be outstanding, and they may be completed out of order. For instance, process 'A' needs to read a block. The request is sent to the drive, the disk head starts to move, and process 'A' blocks waiting for it. Then, process 'B' is allowed to run; it also reads a block from the disk. Process B's block may be sitting in a RAM cache on the SCSI controller, or on the drive itself. Or the block may be closer to the head than process A's block, or on a different drive on the same cable. SCSI allows process B's request to be completed ahead of process A's, which means that process B can be running sooner, so that the most expensive chip - the system CPU - tends to spend less time twiddling its thumbs. Under ATA, the process B request cannot even be sent to the drive until the process A request is complete. These SCSI capabilities are very valuable in a true multi-tasking environment, especialy important in a busy file server, and useless under DOS, which cannot take advantage of them.
I tend to hear from people, 'Well, I never use multitasking' because they never actively run two programs at once - all but one are 'just sitting there'. Consider what happens though, when you minimize a window which uncovers parts of four other application windows. Each of those applications is sent a message telling it to update part of its window; under win95, they will all run concurrently to perform the update. If they need to access disk (usually because of virtual memory) the smoothness of the update can depend a lot on the disk system's ability to respond to multiple independent read requests and finish them all as quickly as possible; SCSI is better at this.
So, yes, ATA can be faster under DOS; but SCSI provides advantages which are inaccessible to DOS. They will benefit Win95 however. The cost of intelligent, fast SCSI controllers and drives should decrease as people discover these advantages and start buying them.
I should add that many of SCSI's advantages are NOT available with some of the simpler SCSI controllers which were targeted only to the DOS market or part of cheap CDROM add-on kits.
Furthermore, SCSI allows far greater flexibility of interconnect. I concede that for the mass market, which likes to buy pre-configured machines, this is but a small advantage.
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QUESTION: Can I have both IDE/ATA
drives and SCSI in the same system?
ANSWER From: Gary Field (gfield@zk3.dec.com)
The short answer is YES. There are a few issues to consider however.
The main issue is which device will be used for booting the system. Under MSDOS, The system BIOS determined this completely. A couple third party BIOSes (like MRBIOS) allowed the user to choose the boot source, but most conventional BIOSes just booted from the IDE if it was present. If no IDE was present then the standard option card BIOS scan would find the SCSI card's BIOS and use it to boot.
Under Windows 95 and Windows NT, there are more options. Since the motherboard BIOS is used to load the boot sector that will still happen according to the same rules as under MSDOS described above. After the boot sector is loaded, the O/S's device drivers take over and those can be unloaded or drive letters re-ordered via the O/S configuration tools.
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QUESTION: Is it possible for two
computers to access the same SCSI disks?
ANSWER From: burke@seachg.uucp (Michael Burke)
Yes, two (or more) systems can be on the same SCSI bus as SCSI disk and tape drives. As long as the SCSI requirements are met - cable lengths, termination and type - the devices can share the SCSI bus.
[Editor(GF): Each host adapter needs to have a unique ID just as the devices do. Some adapters don't let you set this. ]
The question should be - Are there any O/S' that will allow the sharing of file systems? It would not make sense for two hosts to go about treating shared disks as if they each owned the device. Data would be destroyed pretty quickly.
[Editor(GF): CDROM drives can be shared pretty easily because they are by definition READ-ONLY]
Disks can be best shared by having two (or more) partitions on a disk. Each host "owning" its own file system.
[Editor(GF): You also need to watch out for host adapters that reset the bus when booting. Some adapters let you control this. ]
[ Additional editorial comment Editor(GF):
The above discussion refers primarily to PCs. There are high end systems that do allow sharing SCSI devices. Usually, this is to allow fault tolerance. Two systems are connected to the same set of SCSI storage devices and when one of them fails, the other takes control. AIX with HACMP, Digital UNIX with ASE/TCR, and Digital VMS are examples of systems that allow this.
- Thanks to Cees de Groot for suggesting this addition.]
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QUESTION: Is it possible for two
computers to access the same SCSI tape?
ANSWER From: Gary Field (gfield@zk3.dec.com)
Yes, this is not usually as problematic as sharing disks as long as the operator is sensible about what is attempted.
Some things you need to watch out for:
ANSWER From: Scot Stelter, Adaptec (Product Manager for the AHA-1540)
Several articles lately have cited the importance of SCSI-2-compliant cables when cabling SCSI bus subsystems. Perhaps the most accurate and technically detailed one was published in Computer Technology Review in March '93 (Volume XIII, No. 3. PP. 6). In short, it explains the double-clocking mechanism that can occur due to cables whose impedance falls below the 90-Ohm SCSI-2 spec. Steep edge speeds on the REQ and ACK lines of the SCSI bus exacerbate the problem, but non-compliant cables are the root cause. Both LAN TIMES in the US (5/24/93, page 115) and CT Magazine in Germany (7/93, page 18) cite this cable problem.
In an extensive survey of cables available in the US and Europe, we found that more than half of the cables available have single-ended impedances in the 65 to 80 Ohm range -- below the 90 to 132 Ohms specified in the SCSI-2 spec. It seems that some (not all) cable vendors do not understand the specification, describing their cables as SCSI-2 compliant when they are not. A common misconception is that SCSI-2 means a high-density connector. In fact, there are several connector options. I have published a technical bulletin that summarizes the critical requirements (TB 001, April 1993). An artifact of its faster design left the AHA-1540C with faster edge-speeds than its predecessor, the AHA-1540B. As I have said, this can exacerbate the effect of bad cables. This explains why some users could get their AHA-1540B to work when an early AHA-1540C might not.
Essentially, the 1540B was more forgiving than the early 1540Cs. Good cables fixed the problem, but unfortunately for the user, good cables are hard to find.
After surveying the cable market and many of our customers, we decided that bad cables were going to be here for a while, and we had to make the 1540C as forgiving as the 1540B was. At the end of April '93 we made a change to the AHA-1540C that involved using a passive filter to reduce the slew rate of the ACK line, the signal that the host adapter drives during normal data transfers. Extensive testing with many intentionally illegal configurations confirms that we succeeded. Prior to release, we tested the AHA-1540C with over 200 peripherals, systems and demanding software programs with no failures. Then, a second team retested the AHA-1540C across a wild combination of temperatures, humidities and other stresses. This testing gives me confidence that the AHA-1540 line continues to serve as the gold standard for SCSI compatibility.
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QUESTION: What is the difference
between the Adaptec 1542A and 1542B?
ANSWER From: fishman@panix.com (Harvey Fishman)
The AHA-1542A is obsolete and no longer supported by Adaptec. They stopped providing firmware upgrades at some level prior to the equivalence to the 3.10 level of the AHA-1542B firmware. I am not sure just where though. The present latest AHA-1542B firmware is version 3.20, and supports drives up to 8GB under MS-DOS.
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QUESTION: What are the differences
between the Adaptec 1542B and the 1542C?
ANSWER from: Terry Kennedy (terry@spcvxa.spc.edu)
The 1542C is an an updated model which replaces the 1542B. The 1542C features jumperless setup, having only 8 DIP switches. All other configuration options are set using the 1542C's built-in BIOS configuration utility. Configurable features not found on the 1542B are:
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QUESTION: What are the differences
between the 1542C and the 1542CF?
ANSWER from: Terry Kennedy (terry@spcvxa.spc.edu)
The 1542CF includes all of the 1542C features, and adds "Fast" SCSI operation, providing SCSI data rates of up to 10MB/sec (compared with an upper limit of 5MB/sec on the 1542C). This is unrelated to the host DMA rate. It also has a software configurable address for the floppy controller and a "self-healing" fuse for termination power.
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QUESTION: Where can I get SCSICNTL.EXE
and other Adaptec files?
ANSWER From: randy@psg.com (Randy Bush)
and Timothy Hu timhu@ico.isc.com
ftp.psg.com:~/pub/adaptec/...
SCSICNTL.EXE.Z
adse.dd
adse.dd.readme
list
os2drv.zip
scsi_drv.Z
scsi_drv.readm
update.pkg.Z
"list" is a file that describes all the files in this directory.
You can get the ASPI specs from Adaptec's Bulletin Board (408)945-7727.
[Editor(GF): You can also get ASPI spec's from Adaptec's WWW server.]
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QUESTION:What kinds of Optical Drives
are available?
The previous answer From: joungwoo@mensa.usc.edu (John Kim) has been replaced with an updated version.
ANSWER From: Psycho Bob <honge@creighton.edu>[Editor(GF)]
DATE: Sep 18, 1996
As magnetic recording approaches the current engineering limit, more and more attention is paid to optical storage solutions. Optical storage has good points going for it; Immunity to stray magnetic field; Potential for higher storage capacity per unit area; and relatively low media cost.
Although CD-ROM and CD-R are also optical storage units, they are not rewritable -- that puts them out as either secondary storage or primary backup storage for most of us. There is an upcoming sub-format called CD-E ("E" for erasable) that is suppose to become available in late 1996, but I haven't seen much news or even definite rumors. With the advent of DVD, the CD-E may only be a temporary stepping stone to recordable DVDs.
[Editor(GF): CD-E apparently became CD-RW and as of Apr. 1998, there is still much confusion about what recorable DVD will consist of.]
Currently, the most popular optical storage format is magneto-optical (MO) format. It was the only popular rewritable optical storage disc technology before Panasonic's phase-change double-function (PD) format came out in 1995.
Magneto-Optical
As the name implies, MO uses both magnetic and optical technology to store data on the disc. The disc itself is rare earth metal substrate. When data is to be written, the particular spot is first heated by the laser to the Curie point, and the magnetic field is generated while the spot cools. By varying the magnetic field angle, the substrate is polarized in a certain way such that it will reflect the laser beam differently depending on the magnetic field angle present when the particular spot was cooling down.
MO comes in many sizes and capacities. Consumers were first exposed to MO in Steve Jobs' NeXT computer in the mid-1980s. Although 5.25" had a slow start due to initial high cost, it has been evolving quite nicely.
The more popular ISO capacities for 5.25" MO are 2.4GB/2.6GB, 1.2GB/1.3GB, and the 600MB/650MB. In 3.5" form, MO is available in 540MB/640MB, 230MB, and the 128MB. There are also some 12" MO, 14" MO, and other odd sizes in odd capacities. But they are limited to niche markets.
Sony MiniDisc-Data Derived from the Mini-Disc (MD) audio format Sony introduced, MD-Data is to MD as CD-ROM is to digital audio compact disc (CD-DA). MD-Data (and digital audio MD) is based on the same magneto-optical technology, which explains the high-cost of the consumer MD audio units.
MD-Data is the smallest of the MO family. With 2.5" form factor, it can store 140MB of uncompressed data. Current MD-Data drives are rather slow at 150KB/sec sustained transfer rate, but Sharp is hoping to change that.
Sharp will (hopefully) ship a 300KB/sec by the end of 1996, with a second generation of MD-Data available by sometime in 1997. The current schedule from Sharp indicates the second generation MD-Data will be able to store up to 700MB with 600KB/sec transfer rate.
The most important technical advancement MD-Data brought for MO in general is the one-pass recording. Prior to 5.25" 2.4GB/2.6GB MO and 3.5" 540MB/640MB MO, almost all MO used two passes to write data onto the disc -- one pass to erase the whole track, and a second pass to write the updated data. MD's one pass recording, called light intensity modulation, direct over-write (LIM-DOW, ISO 14517) will be in almost all the future MO formats until another better technology comes along.
Just like CD, MD-Data comes in various flavors -- rewritable, write-once, and read-only cartridges. There is also a hybrid disc for MD and MD-Data that is part read-only, and part rewritable.
Panasonic phase-change double-function (PD):
In around mid-'95, Panasonic released a proprietary optical storage format called phase-change double-function (PD) drive. The PD uses substrate that will reflect the light differently when heated to different temperatures. Write-once-read-multiple (WORM) drives were actually the first phase-change formats, but PD is the first *reversible* (that is, re-writable) phase-change format. Current PD stores 650MB per PD cartridge.
Currently, PD's only advantage over its MO brethren is the PD drive's ability to read regular CD-DA and CD-ROMs. The PD rewritable cartridge is not usable in regular CD-ROM drives.
WORM and CD-R:
Both write-once-read-multiple (WORM) and compact disc recordable (CD-R) are both write-once formats -- once you have written the data to the disc, the data cannot be changed. Put another way, the disc media can only be used once. For long term archival of data that need not be changed, it makes sense -- as CD-R media price is unbeatable [As of mid 1996, 650 MB CD-R media sells for $6 to $8 each or about 1 cent per MB!] . Current CD-R offers maximum of 650MB per disc. [Editor(GF) As of Apr. 1998 the price of CD-R media has dropped to about $2 per disc.]
WORM was the first popular format for optical storage, before being eclipsed by MO. WORM is still used by big companies and the government for archival purposes since it has the characteristic of not being able to be altered wihout damaging the media (good audit trail).
The new WORM formats being introduced are tending to be more proprietary. There is rarely any interchangability between different vendor's drives and media.
During the WORM to MO transition, a curious format called continuous composite write-once (CCW) appeared. CCW cartridges function as WORM cartridges, writable using the installed base of WORM drives. But put it into MO drive, CCW cartridges becomes rewritable. Simply put, CCW is MO in WORM's clothing. Many of today's 5.25" MO drives still have the capability to read CCW cartridges.
The future:
Almost all the formats mentioned above have future plans -- usually an "improved version" with faster and more storage capacity. The 5.25" MO camp is shooting for the 4.8GB/5.2GB range, with faster sustained transfer rate in writing data. 3.5" may double their 650MB soon by using both sides of the disc. PD may also double the storage space by using both sides of the disc. But currently it's doubtful as DVD has pretty much been finalized. It'll be interesting to see how Panasonic will interpret the PD in the DVD marketplace (DVD-PD?). DVD-RAM is rumored to use phase-change technology.
The same goes for CD-E, the latecomer of the bunch. If the CD-E is truly playable in ordinary CD-ROM (and audio CD player), it'll probably become the optical storage standard in all but the high-capacity, high-end/server market.
Summary of optical disk formats
Format * |
Physical Size |
Capacity per disk |
Bytes per sector |
# of sides |
Capacity per side |
Standard |
MO 1p |
2.5" |
140MB |
2048/ 2336 |
Single |
140MB |
Sony MD-Data |
MO 2p |
3.5" |
128MB |
512 |
Single |
128MB |
ISO/IEC 10090, ECMA 154 |
MO 2p |
3.5" |
230MB |
512 |
Single |
230MB |
ISO/IEC 13963, ECMA 201 |
MO 1p |
3.5" |
540MB 640MB |
512 2048 |
Single Single |
540MB 640MB |
DIS(ISO/IEC) 15041 |
MO 2p |
5.25" |
600MB 650MB |
512 1024 |
Dual Dual |
296MB 322MB |
ISO/IEC 10089 ANSI X3.2121-1992 |
MO 2p |
5.25" |
1GB 1GB |
512 1024 |
Dual Dual |
463MB 510MB |
ISO 13481 |
MO 2p |
5.25" |
1.2GB 1.3GB |
512 1024 |
Dual Dual |
595MB 650MB |
ISO/IEC 13549 and ECMA 184 |
MO 1p |
5.25" |
2.4GB 2.6GB |
512 1024 |
Dual Dual |
2.3GB 1.3GB |
DIS(ISO/IEC) 14517 |
MO 2p |
5.25" |
1.5GB |
4096 |
Dual |
750MB |
Panasonic |
MO 1p |
5.25" |
4.6GB |
1024 |
Dual |
2.3GB |
Pinnacle Micro "Apex" |
MO |
12" |
8GB |
Nikon |
|||
MO |
12" |
3.2GB |
Sony |
|||
MO |
14" |
6.8GB 10.2GB 14.8GB |
1024 1024 1024 |
Dual Dual Dual |
3.4GB 5.1GB 7.4GB |
Kodak System 2000 |
WORM |
5.25" |
2.6GB |
DIS(ISO/IEC) 15486 |
|||
WORM |
5.25" |
650MB |
Single |
650MB |
ISO/IEC 9171 Format A |
|
WORM |
5.25" |
470MB 940MB 1.4GB |
Single Dual |
470MB |
Panasonic |
|
WORM |
12" |
15GB |
Sony |
|||
PD 1p |
5.25" |
650MB |
4096 |
Single |
650MB |
Panasonic |
CD-R |
5.25" |
650MB |
2048 |
Single |
650MB |
|
CD-E |
5.25" |
650MB |
Pending... |
|||
DVD-ROM |
5.25" |
4.7GB 9.4GB 17GB |
2048 2048 2048 |
Single 2layer dual |
4.7GB 9.4GB 9.4GB |
UDF ISO-13346 |
*technology: 1p -- one-pass write 2p -- two-pass writeStandards for storage are set by many organizations. International Standards Organization (ISO), European Computer Manufacturers Association (ECMA), Deutsche Institut fur Normung (DIN), Japanese Industrial Standards Committee (JISC), and American National Standards Institute (ANSI) set the main optical disc storage standards. The ISO standards take precedence over all other standards.
In the above table, the heading defines one standard -- e.g. 5.25" MO 1.2GB/1.3GB has both ISO 13549 and ECMA 184 listed for it. IT IS NOT THAT 1.2GB FOLLOWS ISO 13549 AND 1.3GB FOLLOWS ECMA 184.
Of CD standards...
Funny as it seems, CD is actually considered as a proprietary format made by Sony and Phillips. The physical format for derivatives like CD-ROM and CD-R are "written in mutual agreement" in form of Red Book, Yellow Book, Orange Book, etc.
Of bytes/sector and usability...
As many of you might notice (especially on 5.25" MOs), there are different sized sectors. Many O/Ses assume one sector to contain 512 bytes. If you buy any of the media that use different than 512 byte/sector, you will need a software driver of some sort to use the media.
In optical media, the sectors are "hard sectored" at factory -- in other words, you cannot change the number of sectors by reformatting (low-level formatting) them. Take the 5.25" 1.2GB/1.3GB MO for example again. The 1.3GB media is sectored at 1024 bytes per sector. So the 1.3GB media has total of 637,041 sectors (per side) on it. If you do not use a software driver and your operating system does not properly recognize it, the 1.3GB media will become a 650MB cartridge (~325MB per side)!!
The safest bet is to use the 512 bytes/sector media. That should make the drive and media usable on most operating systems.
Addendum: (11/15/96)
Sony and Phillips have just announed finalization of compact disc re-writable (CD-RW), together with HP, Matsushita, etc. Long story short, the CD-RW uses phase-change media -- same as Panasonic proprietary PD format. Not only that, it also stores 650MB like PD. And also like the PD, the CD-RW media cannot be read in existing CD-ROM drives! CD-ROM drives manufactured in 1997 and after will read CD-RW discs though.
So, the good news is that CD-RW is here. The bad news is that it's as proprietary as Panasonic's PD in compatibility with current installed base of CD and CD-ROM players.
Table of Contents
QUESTION: Where can I get various
SCSI documentation?
Thanks to John Lohmeyer of Symbios Logic, a number of SCSI related files are available for anonymous ftp.
The archive contains a large amount of data relating to SCSI, and ESDI as well as SCSI-2, IPI, and Fiber Channel, as well as the last revision of the SCSI-1 and SCSI-2 standards before they went into publication by ANSI.
This information server is maintained by Symbios Logic (formerly NCR Corp., formerly AT&T Global Information Solutions) in the hope of returning some value to the Internet community. It contains information about commercial products, and also about computing-related topics in which Symbios Logic as a company, or individuals therein, have interest and expertise.
The information is accessible from several sources:
anonymous ftp to ftp.symbios.com
WWW: http://www.symbios.com/x3t10
Table of Contents
QUESTION: How can I find out about
the emerging SCSI standards?
ANSWER From: Milton Scritsmier (milton@arraytech.com)
The X3T10 committee has opened up a WWW site. It has an overview of SCSI-3, as well as pointers to the WWW sites for the three serial interfaces (FC, SSA, and P1394), and a pointer to an online copy of a proposed SCSI-2 spec.
Here is the original announcement:
Subject: New X3T10 Home Page
Date: Thu, 31 Aug 95 14:07:00 MDT
With a LOT of help from Carey Harrington (Thank you!), X3T10 now has a World Wide Web home page. If you have a web browser, you may want to check out:
John Lohmeyer, Chair X3T10 Technical Committee
ANSWER #2 From: Gary Bartlett (garyb@abekas.com)
A draft version of the SCSI-2 spec is in HTML form on the WWW at:
ANSWER #3 From: Gary Watson (trimm@netcom.com)
Small Form Factor (SFF) Committee documents are available by FaxAccess at:
(408) 741-1600 You will be asked to order documents by number.
For example: to get information on the Single Connector Attach spec.
The SCA-1 spec. is document #8015
The SCA-2 spec. is document #8046
document #8000 is an index to the other documents.
[Editor(GF): you might try: http://playground.sun.com/pub/SCA/SCAR3-2.txt]
This FaxAccess service is available to all, but please keep in mind that unless you have engineering-level understanding of peripheral interfaces, you _will_not_ be able to understand any of it and you are wasting your own time and the bandwidth of these resources. If you are trying to learn more about SCSI, you are better off reading the magazine articles and books listed elsewhere in this FAQ.
The SCSI, SFF, SSA, and Fibre Channel reflectors:
A list of these is available on the Symbios WWW site.
"The SCSI, SFF, SSA, and Fibre Channel reflectors are for review and commentary on the respective specifications, not for asking questions about the interfaces (unless related to a specific ambiguity in a specification) nor for recruiting nor for technical support nor any purpose other than what is stated. The reflectors _are_ available for public review and commentary as required by ANSI and ISO."
Any spec on the reflectors or on the BBS or on the ftp sites are **proposed** or **preliminary** and are often subject to major substantive changes during the committee process. Actual, released, final specs are *only* available from Global Engineering Documents.
ANSWER #4 From: Gary Field (gfield@zk3.dec.com)
For Fibre Channel Association:
Table of Contents
QUESTION: Where can I get official
ANSI SCSI documents?
ANSWER #1 From: kev@hpcpbla.bri.hp.com (Kevin Jones)
and jmatrow@donald.WichitaKS.NCR.COM (John Matrow)
The SCSI specification: Available from:
ANSI
11 West 42nd St. - 13th floor
New York, NY 10036
Sales Dept. (212) 642-4900
OR
Global Engineering Documents
15 Inverness Way East
Englewood Co 80112-5704
(800) 854-7179 or (303) 792-2181
Int'l Sales Fax: (303) 397-2740
SCSI-1: X3.131-1986
SCSI-2: X3.131-199x
SCSI-3 X3T9.2/91-010R4 Working Draft
[Editor(GF):] The official ANSI standards are NOT available free of charge from any source. Only draft versions are freely distributable.
Table of Contents
QUESTION: What SCSI books and
tutorials are available?
ANSWER From: Gary Field (gfield@zk3.dec.com)
IN-DEPTH EXPLORATION OF SCSI can be obtained from Solution Technology, Attn: SCSI Publications, POB 104, Boulder Creek, CA 95006, (408)338-4285, FAX (408)338-4374
THE SCSI ENCYLOPEDIA and the SCSI BENCH REFERENCE can be obtained from ENDL Publishing, 14426 Black Walnut Ct., Saratoga, CA 95090,
(408)867-6642, FAX (408)867-2115
SCSI: UNDERSTANDING THE SMALL COMPUTER SYSTEM INTERFACE was published by Prentice-Hall, ISBN 0-13-796855-8 (Seems to be out of print)
A neat little book called "Basics of SCSI" second edition, was sent to me free of charge by Ancot Corporation, Menlo Park, CA (415) 322-5322. It gives a simplified description of how most aspects of the SCSI bus work and includes some discussion of SCSI-2 issues.
"The book of SCSI - A guide for Adventurers" by Peter M. Ridge.
Published by No Starch Press, Daly City, CA,
ISBN # 1-886411-02-6, List Price $34.95.
Contains general coverage of most aspects of SCSI.
http://www.nostarch.com/scsi.htm
"Programmer's Guide to SCSI" with CDROM - by Brian Sawert.
Published by Addison Wesley, Reading, MA. SRP $39.95
ISBN # 0-201-18538-5
Includes a chapter on UNIX SCSI subsystems written by Gary Field.
http://cseng.awl.com/bookdetail.qry?ISBN=0-201-18538-5&ptype=0
Addition by: (kyrrin2@wizards.net)
'The SCSI Bus and IDE Interface' 2nd edition by Friedhelm Scmidt,
Addison-Wesley Publishing, $34.95 (I think). It includes a diskette with examples of source code to handle SCSI and IDE devices from a low-level programmer's perspective, and it has very detailed technical descriptions of both subsystems.
Not a book for beginners, but I heartily recommend it for anyone who's serious about learning the technical ropes.
ANSWER #2 From: Runar Jorgensen (runar.jorgensen@fys.uio.no)
There was a two part article in Byte Magazine. The first part was in Feb 1990 issue, p. 267-274 and the second was in Mar 1990 issue, p. 291-298.
Another two part article appeared in Byte in May 1986 and June 1986.
Table of Contents
QUESTION: Where can I find SCSI
info on the Web?
ANSWER FROM: Gary Field (gfield@zk3.dec.com)
Try some of these:
http://www.bandwidth.net/scsi.html
http://www.adaptec.com/support/files/miscellaneous.html
Table of Contents
QUESTION: Where can I get information
on various disk drives and controllers?
ANSWER: ekrieger@quasar.xs4all.nl (Eric Krieger) (Updated Sep. 30, 1994)
Drive and Controller Guide, Version 4.3
THEREF(tm) is a comprehensive Directory of Hard Drives, Floppy Drives, Optical Drives, and Drive Controllers & Host Adapters. It is designed to help the novice and pro alike with integration problems and system setups.
Information is provided in two handy formats; Portrait mode, for those who prefer a normal book-binding type print format, and(or) do not have a printer with Landscape capability, and Landscape mode, for those who pre-fer a computer-printout type format.
For printing, a Laserjet is preferred, but not necessary, and setup info is provided. For viewing, LIST(tm) by Vernon Buerg, will provide an excellent result, and allow text searches for finding specific models.
By F. Robert Falbo
Due many reports about the unavailablity of this file/archive I made sure that the file does exist at the following site:
You should find the archive at:
/pub/doc/hardware/harddisks/theref43.tar.gz
/pub/doc/hardware/harddisks/theref43.readme
(In that directory-path there is also a sub-directory Seagate, where you also can find info/files about Seagate-drives).
Before you actually get this file, be sure to get/read the file /README.FILETYPES since it explains the used file-extension and which (de-)archiver should be used (and where to find/get them!).
Note: In the archive there are files containing Extended ASCII or ANSI characters (mostly used with IBM- and compatible PC's), so it may be a bit unreadable when reading it on non-PC systems, or without using a proper Characterset/Font!
TheRef is also available via WWW from:
Table of Contents
QUESTION: Where can I get technical
information and jumper settings for HP drives?
ANSWER From: Rodney Brown (RBrown@cocam.com.au)
Update From: Martin C Mueller (mcm@mathematik.uni-kl.de )
HP SCSI Storage Device Support Pages
http://www.hp.com/isgsupport/index.html
Table of Contents
QUESTION: How can I contact Adaptec?
Also: Future Domain, Corel CD Creator, Trantor, Incat systems.
ANSWER From: jcaples@netcom.com (Jon D Caples)
Adaptec's general inquiry number, 800-959-7274, affords access to a FAX-based information retrieval system. In order to preserve the accuracy of this information, I won't go into details about how to use it (since Adaptec may change things without telling me :) ).
For those outside the CAN-US area, or local to Adaptec the direct FAX info number is (408) 957-7150.
There are three general topics as of this writing:
[Editor(GF): As of July 1993 Adaptec bought Trantor.
Try (800) 872-6867 (TRA-NTOR)]
World Wide Web (WWW) URL: http://www.adaptec.com/
[(from: Andrew Lockhart (andrew@interact.manawatu.planet.co.nz) ]
You can address Adaptec support by email. The address is support@adaptec.com. An auto-responder will bounce a message back acknowledging receipt of your email. This message will also detail other current forms of Adaptec Technical support. They promise a, no more than, 5 day turn-around. We have found the response brief, but satisfactory to our needs. We should add, we mention we are Dealers in our email (which may improve Adaptec's response).
Table of Contents
QUESTION: How can I contact Archive
Corporation?
[Editor(GF)]
Archive was bought by Conner Peripherals in 1993
Table of Contents
QUESTION: How can I contact BusLogic/Bustek/Mylex?
ANSWER From: Gary Field (gfield@zk3.dec.com)
Table of Contents
QUESTION: How can I contact Corel?
ANSWER From: Gary Field (gfield@zk3.dec.com)
ANSWER From: Gerrit Visser (gerrit@isgtec.com)
For Corel CD Creator Software contact Adaptec
Table of Contents
QUESTION: How can I contact Fujitsu?
ANSWER From: Ken Porter (72420.2436@compuserve.com)
Fujitsu FactsLine FAX Back service (408) 428-0456
A six page catalog of available documents can be ordered.
ANSWER From: Mike Henry (anonymous)
A while back, Fujitsu created a product called Fujitsu Knowledge System (FKS) (long available on Compuserve (GO FUJITSU)). It is a Windows Help File (.HLP) listing of many Fujitsu disk, tape, and optical products. It includes drive switch/jumper settings and meanings. It is available via anonymous ftp from ftp.intellistor.com in the /pub/fks directory, filename: fks.exe
It is self-extracting and mostly self-documenting.
Table of Contents
QUESTION: How can I contact Quantum?
ANSWER From: kmartine@qntm.com (Kevin Martinez)
Table of Contents
QUESTION: How can I contact Seagate?
ANSWER From: John McDonald (John_McDonald@notes.seagate.com)
Technical Support Services
Online Services
Using a modem, you can obtain troubleshooting tips, free utility programs, drive specifications, and jumper settings for Seagate's entire product line. You can also download software for installing and analyzing your drive.
You can obtain technical information about Seagate products over the Internet from Seagate's World Wide Web home page (http://www.seagate.com), Seagate's FTP server (ftp://ftp.seagate.com) or e-mail. Send your e-mail questions to DiscSupport@seagate.com or TapeSupport@seagate.com.
SeaBOARD is a computer bulletin board system that contains information about Seagate disc and tape drive products and is available 24 hours daily. Set your communications software to eight data bits, no parity and one stop bit (8-N-1).
Location Phone number
You can use a touch-tone telephone to access Seagate's automated FAX system to receive technical support information by return FAX. This service is available 24 hours daily.
Location Phone number
You can FAX questions or comments to technical support specialists 24 hours daily. Responses are sent during business hours.
Location Phone number
1-800-SEAGATE
Seagate's 800 number (1-800-732-4283) allows toll-free access to automated self-help services that provide answers to commonly asked questions, troubleshooting tips, and specifications for disc drives and tape drives. This service is available 24 hours daily and requires a touch-tone phone. International callers can reach this automated self-help service by calling 405-936-1234.
For one-on-one help, you can talk to a technical support specialist during local business hours. Before calling, note your system configuration and drive model number (STnnnn).
Location Phone number
Conner Peripherals was bought by Seagate
Table of Contents
QUESTION: How can I contactMaxtor?
ANSWER From: David G North (D_North@tditx.com)
Main Number: (800) 262-9867 (Has FAXback feature for drive info etc)
ftp site: ftp.maxtor.com (New!)
ANSWER From: Eric Van Buren (vanburen%flovax.dnet@rocdec.roc.wayne.edu)
Table of Contents
QUESTION: How can I contact NCR?
NCR Microelectronics division was bought by AT&T and then by Symbios Logic.
See "How can I contact Symbios Logic"
Table of Contents
QUESTION: How can I contact Philips?
ANSWER From: S. C. Mentzer (smentzer@anes.hmc.psu.edu)
Philips Consumer Electronics Co.
One Philips Drive
Knoxville, TN 37914-1810
(615) 521-4316
(615) 521-4891 (FAX)
[Editor(GF)]
Table of Contents
QUESTION: How can I contact Symbios
Logic?
ANSWER From: Symbios Logic
Update From: Wade Adams (link@vantek.net)
[Editor(GF)]: In Feb., 1998, Adaptec attempted to purchase Symbios Logic. The Federal Trade Commission told them they couldn't and subsequently, Symbios was sold to LSI Logic.
For literature on any Symbios Logic product please contact:
Phone: (800) 636-8022
(800) 856-3093
email: literature@symbios.com
Technical Support:
Phone: (719) 533-7230
Table of Contents
QUESTION: How can I contact UltraStor?
(Out of business)
ANSWER From: Ultrastor
UltraStor Corporation
13766 Alton Parkway suite 144
Irvine, CA 92718
General (714) 581-4100
Tech. Support (714) 581-4016
FAX (714) 581-4102
BBS (714) 581-4125
email: ultrastor@primenet.com
finger: ustor@primenet.com
ftp: ftp.primenet.com:users/u/ustor
ANSWER From: Ben Mehling (bmehling@uci.edu)
I am setting up a "unauthorized" UltraStor site for the orphaned customers and cards still out there.
I do not think the above numbers are good anymore.
The 4100 line will get you Power I/O (an unrelated Adaptec holding) and the 4016 line may get you a dead-end answering service. The company is no longer active (as far as I know). The primenet account is alive, but again not active. These links are to the "Unauthorized" UltraStor site. This site is in no way affiliated with UltraStor or its holding companies. It is a free "mirror" site for distribution of drivers and information. (hint: we are trying to help out, not provide tech support.)
Try:
UltraStor@kuci.uci.edu (unauthorized).
www.UltraStor (unauthorized).
ftp.UltraStor (unauthorized).
The above three addresses are hypertext linked to these addresses:
The web site address is: http://www.kuci.uci.edu/~ustor/
The FTP site address is: falco.kuci.uci.edu/users/ustor
The mail/finger address is ultrastor@kuci.uci.edu / ustor@falco.kuci.uci.edu
The current maintainers are:
Ben Mehling (bmehling@uci.edu)
Phil Colline (pcolline@falco.kuci.uci.edu)
Table of Contents
QUESTION: How can I contact Tecmar
Technologies (formerly Wangtek, WangDAT,Sytron, and Rexon)?
ANSWER FROM: from: Jay Long - (jayl@mfltd.co.uk) and
Peter Dyballa (pete@riese.thi.informatik.uni-frankfurt.de)
Tecmar Technologies, Inc.
1900 Pike Rd., Bldg. E
Longmont, CO USA
phone: (303) 682-3700
(303) 776-7706
FAX: (303)776-1085
faxback: (800) 4BACKUP
European Office
Unit 15 Suttons Business Park
Suttons Park Avenue
Earley, Reading, UK RG6 1AZ
(44) 1189-660063
(44) 1189-660065 FAX
Singapore Office
Blk. 35 Marsiling Industrial Estate Road 3 #05-01/ 06
Singapore 739257
(65) 269-2228
(65) 360-0888 fax
Table of Contents
QUESTION: How can I contactWestern
Digital?
ANSWER From: FILIPG@PARANOIA.COM
Address:
Western Digital Corporation
8105 Irvine Center Drive
Irvine, CA USA 92718
Online Services:
Tech Support BBS 714-753-1234 (up to 28.8 KBS)
WWW: http://www.wdc.com/
FTP ftp.wdc.com
AOL (keyword) WDC or Western Digital
MSN (go word) WDC
Table of Contents
QUESTION: How can I contact DPT
(Distributed Processing Technology)?
ANSWER: From: Gary Field (gfield@zk3.dec.com)
voice: (407) 830-5522
FAX: (407) 260-6690
[Editor(GF)]
WWW: http://www.dpt.com/
Table of Contents
QUESTION: How can I contact Micropolis?
ANSWER: From: Richard Ravich (Richard_Ravich@microp.com)
[Editor(GF): As of late 1997 Micropolis is now out of business -- RIP. You might try http://www.blue-planet.com/tech/ for drive info. ]
Table of Contents
QUESTION: How can I contact Legacy
Storage Systems?
ANSWER: From: Gregory Smith (GREGS@lss-hq.mhs.compuserve.com)
General: (905) 475-1077
Sales/Tech support/Service: (905) 475-0550
U.S. Tech Support: (800) 361-5685
Fax: (905) 475-1088
Mail:
Legacy Storage Systems
43 Riviera Drive
Markham, ON Canada L3R 5J6
Table of Contents
QUESTION: How can I find out about
IBM hard disks?
ANSWER: From: Gary Field (gfield@zk3.dec.com)
http://www.storage.ibm.com/hardsoft/diskdrdl/hddsprt.htm
Table of Contents
QUESTION: What is FAST SCSI?
ANSWER From: kev@hpcpbla.bri.hp.com (Kevin Jones)
There are 2 handshaking modes on the SCSI bus, used for transferring data:
ASYNCHRONOUS is a classic Req/Ack handshake.
SYNCHRONOUS is "sort of" Req/Ack, only it allows you to issue multiple Req's before receiving Ack's. What this means in practice is that SYNCHRONOUS transfers are approx 3 times faster than ASYNCHRONOUS.
SCSI1 allowed asynchronous transfers at up to 1.5 Mbytes/Sec and synchronous transfers at up to 5.0 Mbytes/Sec.
SCSI2 had some of the timing margins "shaved" in order that faster handshaking could occur. The result is that asynchronous transfers can run at up to 3.0 Mbytes/Sec and synchronous transfers at up to 10.0 Mbytes/Sec.
The term "FAST" is generally applied to a SCSI device which can do syncrhonous transfers at speeds in excess of 5.0 Mbytes/Sec. This term can only be applied to SCSI2 devices since SCSI1 didn't have the timing margins that allow for FAST transfers.
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QUESTION: How can I check a passive
SCSI terminator?
ANSWER From: stevel@coos.dartmouth.edu (Steve Ligett)
With an Ohmmeter:
The terminator contains 18 220-ohm resistors from signals to TERMPWR, and 18 330-ohm resistors from those signals to GROUND. I've drawn that below:
TERMPWR --+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | | | | | | | | | | | | | | | | | | R1 R1 R1 R1 R1 R1 R1 R1 R1 R1 R1 R1 R1 R1 R1 R1 R1 R1 | | | | | | | | | | | | | | | | | | sig o o o o o o o o o o o o o o o o o o | | | | | | | | | | | | | | | | | | R2 R2 R2 R2 R2 R2 R2 R2 R2 R2 R2 R2 R2 R2 R2 R2 R2 R2 | | | | | | | | | | | | | | | | | | --+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ GROUND R1 = 220 Ohms, R2 = 330 OhmsWhen you measure from any one signal to termpower, you aren't measuring that resistor in isolation, you are measuring that resistor IN PARALLEL with the combination of the corresponding 330 ohm resistor plus 17 220+330 ohm resistor pairs in series.
I've redrawn the schematic to make this easier to see: TERMPWR /+---+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | | | | | | | | | | | | | | | | | | | R1 R1 R1 R1 R1 R1 R1 R1 R1 R1 R1 R1 R1 R1 R1 R1 R1 | | | | | | | | | | | | | | | | | | | o o o o o o o o o o o o o o o o o | | | | | | | | | | | | | | | | | | | R2 R2 R2 R2 R2 R2 R2 R2 R2 R2 R2 R2 R2 R2 R2 R2 R2 | | | | | | | | | | | | | | | | | | | --+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | / GROUND R1 | | | | R2 | / o <--------- 17 other pairs in parallel ----------> sigWe're trying to measure that one resistor from a signal to TERMPWR, but there's a ton of other stuff in parallel. The resistance of that "stuff" is 330 + 550/17 ohms (the 330 ohm resistor, in series with a parallel combination of 17 550 ohm resistors). The general formula for the equivalent of two resistances in parallel is R1*R2/(R1+R2).
Whipping out my trusty spreadsheet, I find that the "stuff" has a resistance of about 362 ohms, and that, in parallel with 220 ohms is about 137 ohms.
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QUESTION:Can someone explain to me
the difference between 'normal' SCSI and differential SCSI?
ANSWER From: ralf@wpi.WPI.EDU (Ralph Valentino)
"Normal" SCSI is also called "Single-ended" SCSI. For each signal that needs to be sent across the bus, there exists a wire to carry it. With differential SCSI, for each signal that needs to be sent across the bus, there exists a pair of wires to carry it. The first in this pair carries the same type of signal the single-ended SCSI carries. The second in this pair, however, carries its logical inversion. The receiver takes the difference of the pair (thus the name differential), which makes it less susceptible to noise and allows for greater cable length.
ANSWER From: ralf@wpi.WPI.EDU (Ralph Valentino)
Differential SCSI Connector Pinouts ---------------------------------------- ---------------------------------------- | SCSI | | MINI | | | SCSI | | MINI | | | SIGNAL | DD-50P | MICRO | DD-50SA | | SIGNAL | DD-50P | MICRO | DD-50SA | ---------------------------------------- ---------------------------------------- | -GND | 2 | 26 | 34 | | (open) | 1 | 1 | 1 | | -DB(0) | 4 | 27 | 2 | | +DB(0) | 3 | 2 | 18 | | -DB(1) | 6 | 28 | 19 | | +DB(1) | 5 | 3 | 35 | | -DB(2) | 8 | 29 | 36 | | +DB(2) | 7 | 4 | 3 | | -DB(3) | 10 | 30 | 4 | | +DB(3) | 9 | 5 | 20 | | -DB(4) | 12 | 31 | 21 | | +DB(4) | 11 | 6 | 37 | | -DB(5) | 14 | 32 | 38 | | +DB(5) | 13 | 7 | 5 | | -DB(6) | 16 | 33 | 6 | | +DB(6) | 15 | 8 | 22 | | -DB(7) | 18 | 34 | 23 | | +DB(7) | 17 | 9 | 39 | | -DB(P) | 20 | 35 | 40 | | +DB(P) | 19 | 10 | 7 | | GND | 22 | 36 | 8 | |DIFSENS | 21 | 11 | 24 | | GND | 24 | 37 | 25 | | GND | 23 | 12 | 41 | |TERMPWR | 26 | 38 | 42 | |TERMPWR | 25 | 13 | 9 | | GND | 28 | 39 | 10 | | GND | 27 | 14 | 26 | | -ATN | 30 | 40 | 27 | | +ATN | 29 | 15 | 43 | | GND | 32 | 41 | 44 | | GND | 31 | 16 | 11 | | -BSY | 34 | 42 | 12 | | +BSY | 33 | 17 | 28 | | -ACK | 36 | 43 | 29 | | +ACK | 35 | 18 | 45 | | -RST | 38 | 44 | 46 | | +RST | 37 | 19 | 13 | | -MSG | 40 | 45 | 14 | | +MSG | 39 | 20 | 30 | | -SEL | 42 | 46 | 31 | | +SEL | 41 | 21 | 47 | | -C/D | 44 | 47 | 48 | | +C/D | 43 | 22 | 15 | | -REQ | 46 | 48 | 16 | | +REQ | 45 | 23 | 32 | | -I/O | 48 | 49 | 33 | | +I/O | 47 | 24 | 49 | | GND | 50 | 50 | 50 | | GND | 49 | 25 | 17 | ---------------------------------------- ----------------------------------------
Please note that I can only verify the DD-50P connector. The Mini
Micro and DD-50SA pinout above is a pin for pin mapping from the SCSI
pinout in this FAQ.
====
How can I tell if I have a single ended or a differential drive?
ANSWER From: Gary Field (gfield@zk3.dec.com)
Most times the model number of the drive will end with "D".
Use an Ohm meter to check the resistance between pins 21 & 22.
On a single ended system, they should both be tied together and tied to GND.
On the differential drive, they should be open or have a significant resistance between them. Differential drives are less common than single-ended ones, because they are mainly used only where longer cable runs are necessary, and they are not generally used in PCs, but state of the art drives are available with differential interfaces. Generally only the higher performance drives have a differential option because of the added cost.
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QUESTION: Who manufactures SCSI
extenders and Single-Ended to Differential converters ?
ANSWER From: Gary Field (gfield@zk3.dec.com)
The following companies manufacture SCSI extenders and converters:
Ancot Corporation
115 Constitution Drive
Menlo Park, CA 94025
Tel: (415) 322-5322
Fax: (415) 322-0455
Email: sales@ancot.com
Apcon Inc.
17938 SW Boones Ferry Road
Portland, OR 97224
Phone: (503) 639-6700 Fax: (503) 639-6740
Email: info@apcon.com
Paralan Corporation
7875 Convoy Court, San Diego, CA 92111
Tel. (619) 560-7266 || Fax 619-560-8929
email: scsi@paralan.com
Rancho Technology Inc.
10783 Bell Court-Rancho
Cucamonga-CA-91730
Phone: (909)987-3966; Fax: (909)989-2365;
E-Mail: scsi@rancho.com; BBS: (909)980-7699
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QUESTION: I've got a SCSI disk
with an 80 pin connector. Someone called it an SCA drive. Can I connect
this to my SCSI bus?
ANSWER From: Gary Field (gfield@zk3.dec.com)
Date: Updated September 1998
SCA stands for "Single Connector Attachment". It is a standard being worked on by the ANSI Small Form Factor (SFF) committee. It combines WIDE SCSI signals, Power connections and ID switch connections onto one connector.
The main reason for creating this standard was to make it easier to connect drives in a hot-swappable RAID configuration.
SCSI vendors sell adapters that bring out the three sets of signals to conventional connectors.
One place that sells such adapters is:
(There aren't any host adapters with 80 pin connectors, so don't ask J)
See: http://playground.sun.com/pub/SCA/SCAR3-2.txt for more information about SCA.
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QUESTION: What are the pinouts
for SCSI connectors?
ANSWER From: snively@scsi.Eng.Sun.COM (Bob Snively)
[ Edited and expanded by Gary Field (gfield@zk3.dec.com) ]
Originally dated May 23, 1990
The connector families described by the drawings have standard pin numberings which are described the same way by all vendors that I have encountered. The SCSI-2 specification identifies the standard numbering, using that convention. It happened to be documented by AMP, but all the vendors use the same convention.
The following diagrams have the outline drawings of connector sockets at the bottom. This is really for reference only, because the connector sockets and plugs are both specified as to their numbering and usually are labeled.
-------------------- microSCSI to SCSI Diagram --------------------------- SCSI Connector Pinouts (single-ended) ------------------------------------ ------------------------------------- | SCSI | | MINI | | | SCSI | | MINI | | | SIGNAL| DD-50P | MICRO | DD-50SA | | SIGNAL | DD-50P | MICRO | DD-50SA | ------------------------------------ ------------------------------------- | -DB(0)| 2 | 26 | 34 | | GND | 1 | 1 | 1 | | -DB(1)| 4 | 27 | 2 | | GND | 3 | 2 | 18 | | -DB(2)| 6 | 28 | 19 | | GND | 5 | 3 | 35 | | -DB(3)| 8 | 29 | 36 | | GND | 7 | 4 | 3 | | -DB(4)| 10 | 30 | 4 | | GND | 9 | 5 | 20 | | -DB(5)| 12 | 31 | 21 | | GND | 11 | 6 | 37 | | -DB(6)| 14 | 32 | 38 | | GND | 13 | 7 | 5 | | -DB(7)| 16 | 33 |