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- From: ralf@chpc.org (Ralph Valentino)
- Newsgroups: comp.sys.ibm.pc.hardware.video,comp.sys.ibm.pc.hardware.comm,comp.sys.ibm.pc.hardware.storage,comp.sys.ibm.pc.hardware.cd-rom,comp.sys.ibm.pc.hardware.systems,comp.sys.ibm.pc.hardware.networking,comp.sys.ibm.pc.hardware.chips,comp.sys.ibm.pc.hardware.misc,comp.answers,news.answers
- Subject: comp.sys.ibm.pc.hardware.* Frequently Asked Questions (FAQ) Part 2/5
- Followup-To: comp.sys.ibm.pc.hardware.misc
- Date: 11 Apr 1994 01:33:42 -0400
- Organization: Center For High Performance Computing
- Lines: 1138
- Sender: ralf@chpc.chpc.org
- Approved: news-answers-request@MIT.EDU
- Distribution: world
- Expires: 11 May 1994 00:00:00 GMT
- Message-ID: <2oanfm$f0t@chpc.chpc.org>
- Reply-To: ralf@wpi.edu
- NNTP-Posting-Host: localhost.chpc.org
- Summary: This is a monthly posting containing a list of Frequently
- Asked Questions (and their answers) pertaining to hardware
- and IBM PC clones. It should be read by anyone who wishes
- to post to any group in the comp.sys.ibm.pc.hardware.*
- hierarchy.
- Xref: bloom-beacon.mit.edu comp.sys.ibm.pc.hardware.video:6700 comp.sys.ibm.pc.hardware.comm:2486 comp.sys.ibm.pc.hardware.storage:5012 comp.sys.ibm.pc.hardware.cd-rom:3343 comp.sys.ibm.pc.hardware.systems:2887 comp.sys.ibm.pc.hardware.networking:1848 comp.sys.ibm.pc.hardware.chips:5014 comp.sys.ibm.pc.hardware.misc:4921 comp.answers:4845 news.answers:17889
-
- Archive-name: pc-hardware-faq/part2
- Last-modified: 1994/04/10
- Version: 1.3
-
- S) 3.0 IO controllers/interfaces
-
- Q) 3.1 *How do IDE/MFM/RLL/ESDI/SCSI interfaces work?
-
- Q) 3.2 *How can I tell if I have MFM/RLL/ESDI/IDE/SCSI?
-
- Q) 3.3 Do caching controllers really help?
-
- [From: backbone!wayne@tower.tssi.com (Wayne Schlitt)]
-
- The short answer, is that if you are using a multi-tasking
- operating system with a good memory manager, caching controllers
- should be ignored. If you are running DOS or Windows, then *maybe*
- they will help, but I am not sure that they are a good buy.
-
- There are lots of people who have said "I put a caching controller in
- my computer, and it runs faster!". This is probably true, but they
- never have measured the speed increase compared to putting the same
- memory into main memory instead. More importantly, the caching
- controllers cost more money than non caching controllers, so you
- should be able to add _more_ main memory instead of buying a caching
- controller.
-
- The following is a shortened up version of a much longer article. If
- you want a copy of the longer article, send me email at
- "wayne@cse.unl.edu".
-
- *** Why a multi-tasking operating system?
-
- A multi-tasking operating system can allow the application to continue
- immediately after it does a write, and the actual disk write can
- happen later. This is known as write behind. The operating system
- can also read several blocks from the file when the application
- requests just part of the first block. This is known as read a head.
- When the application requests the block later on, the block will
- already be there and the OS can then schedule some more reads.
-
- A multitasking operating system is required because these operations
- can cause interrupts and processing when control has been given back to
- the application.
-
- Basically, operating systems such as DOS, MS-Windows, MacOS and such
- do not allow true preemptive multitasking and can not do the read a
- heads and the write behinds. For these systems, the latency of a disk
- drive is the most important thing. The application does not regain
- control until the read or write has finished.
-
- *** The controller can't speed up the disk.
-
- Remember, the bottleneck is at the disk. Nothing that the controller
- can do can make the data come off the platters any faster. All but the
- oldest and slowest controllers can keep up with all but the newest and
- fastest disks. The SCSI bus is designed to be able to keep *several*
- disks busy without slowing things down.
-
- Speeding up parts of the system that are not the bottleneck won't help
- much. The goal has to be to reduce the number of real disk accesses.
-
- *** First, isn't the caching controller hardware and isn't hardware
- *** always faster than software?
-
- Well, yes there is a piece of physical hardware that is called the
- caching controller, but no, the cache is not really "in hardware".
- Managing a disk is a fairly complicated task, complicated enough that
- you really can't implement the controller in combinatorial logic.
-
- So, just about all disk controllers and for that matter all disk
- drives have a general purpose computer on them. They run a little
- software program that manages the communication between the main cpu
- and the disk bus, or the disk bus and the disk. Often this cpu is put
- in with a bunch of other logic as part of a standard cell custom chip,
- so you might not see a chip that says "Z80" or such.
-
- So, we are really not comparing "hardware" with "software", we are
- comparing "software on the controller" with "software on the main
- cpu".
-
- *** Ok, why can the OS win?
-
- Assume that you have a bunch of memory that you can either put into
- main memory and have the OS manage the cache, or put on a caching
- controller. Which one will be better? Let us look at the various
- cases.
-
- For a cache hit you have:
-
- If the OS does the caching, you just have the OS's cache checking
- latency.
-
- If the card does the caching, you will have the OS's cache checking
- latency, plus the I/O setup time, plus the controller's cache checking
- latency, plus you have to move the data from the card to main memory.
- If the controller does DMA, it will be taking away from the memory
- bandwidth that the main CPU needs. If the controller doesn't have
- DMA, then the main CPU will have to do all the transfers, one word at
- a time.
-
- For a cache miss, you have:
-
- If the OS does the caching, you have the OS's cache checking latency
- plus the set up time for the disk I/O, plus the time it takes for the
- disk to transfer the data (this will be a majority of the time), plus the
- cost of doing either the DMA or having the CPU move the data into main
- memory.
-
- The caching controller will have all of the above times, plus it's own
- cache checking latency.
-
- As you can see, the caching controller adds a lot of overhead no
- matter what. This overhead can only be offset when you get a cache
- hit, but since you have the same amount of memory on the controller
- and the main cpu, you should have the same number of cache hits in
- either case. Therefore, the caching controller will always give more
- overhead than an OS managed cache.
-
- *** Yeah, but there is this processor on the controller doing the
- *** cache checks, so you really have a multi-processor system.
- *** Shouldn't this be faster than a single processor? Doesn't this
- *** allow the main cpu to do other things while the controller manages
- *** the cache?
-
- Yes, this really is a multi-processor system, but multi-processors are
- not always faster than uni-processors. In particular, multi-processor
- systems have communication overhead. In this case, you are
- communicating with the controller using a protocol that is fairly
- expensive, with outb instructions and interrupts and such. The
- overhead of communicating with this other processor is greater than
- the overhead of just checking the cache on main cpu, even if the main
- cpu is very slow.
-
- The multi-processor aspect just doesn't help out when you are talking
- about managing a cache. There is just too much communication overhead
- and too little processing for it to be a win.
-
- *** Ok, but couldn't the caching controller do a better job of
- *** managing the cache?
-
- Both the controller and the OS are going to be executing a piece of
- software, so in theory there isn't anything that the slower cpu on the
- controller can do that the OS can't do, but the OS can do things that
- the controller can't do.
-
- Here are some of the things that the OS can do better:
-
- * When you read a block from a file, the OS can read several more
- blocks ahead of time. Caching controllers often will read an entire
- track in order to simulate this file read a head, but the rest of
- the file isn't always on the same track, only the OS knows where the
- blocks are really going to be at. This can lead to wasted time and
- cache memory reading data that will never be used.
-
- * In order to improve file system reliability, some writes _must_
- complete immediately, and _must_ complete in the order that they are
- given. Otherwise, the file system structures may not be left in a
- coherent state if the system crashes.
-
- Other writes can be completed as time is available, and can be done
- in any order. The operating system knows the difference between
- these cases and can do the writes appropriately.
-
- Caching controllers, on the other hand, don't know if the write that
- it was just given _must_ be written right away, or if it can wait a
- little bit. If it waits when it shouldn't, you are risking your
- file system and data.
-
- * Sometimes, you want a large disk cache if you are accessing lots of
- data off the disk. At other times, you want a small disk cache and
- more memory left to programs. The operating system can balance
- these needs dynamically and adjust the amount of disk cache
- automatically.
-
- If you put the memory on a caching controller, then that memory can
- _only_ be used for disk caches, and you can _never_ use more.
- Chances are, you will either have too much or too little memory
- dedicated to the cache at any give time.
-
- * When a process closes a file, the operating system knows that the
- blocks associated with that file are not as likely to to be used
- again as those blocks associated with files that are still open.
- Only the operating system is going to know when files are closed,
- the controller won't. Similar things happen with processes.
-
- * In the area of Virtual Memory, the OS does an extremely better job
- of managing things. When a program accesses a piece of memory, the
- CPU will do a hardware level check to see if the page is in memory.
- If the page is in memory, then there will basically be no delay. It
- is only when the page isn't in memory that the OS gets involved.
-
- Even if all of those extra pages are sitting in the
- caching controller's memory, they still have to be moved to main
- memory with all the overhead that that involves.
-
- This is why dynamic caches vs program memory is so important.
-
- *** What is the "Memory Hierarchy" and how does this relate to
- *** caching controllers?
-
- The basic idea of a memory hierarchy is to layer various types of
- memory, so that the fastest memory is closest to the cpu. Faster
- memory is more expensive, so you can't use only the fastest type and
- still be cheap. If a piece of data isn't in the highest (fastest)
- level of the hierarchy, then you have to check the next level down.
-
- In order for a memory hierarchy to work well, you need to make sure
- that the each level of the hierarchy has much more storage then the
- level above it, otherwise you wont have a high hit rate.
-
- The hierarchy on a 486 goes something like this:
-
- 8 regs << 8k on chip cache << 256k off chip cache << main memory << disk
-
- If you are going to put something between main memory and disk, it
- needs to be much larger than main memory in order for it to be
- effective.
-
- *** What about all these neat things that a caching controller can do
- *** such as elevator seeking, overlapping seeks with reads and writes,
- *** scatter/gather, etc...
-
- These are nice features, but they are all done by either the OS or a
- good SCSI controller anyway. None of these things are at all related
- to supporting the cache, so you shouldn't buy a caching controller for
- just these features.
-
- *** Ok, you have talked about things like Unix, OS/2 and Windows NT,
- *** but what about DOS and MS-Windows?
-
- Well, here things get a lot grayer. First, older versions of DOS have
- notoriously bad disk cache programs. Since neither DOS nor MS-Windows
- are preemptive multi-tasking systems, it is much harder to do read a
- head. Also, since DOS/MS-Windows users are used to being able to
- power off their computers at any time, doing write behind is much more
- dangerous. DOS and MS-Windows also can crash much easier than these
- other OS's, so people might reboot for many reasons.
-
- Caching controllers usually leave the hard disk light on when they
- have data that hasn't been written out, and people don't usually power
- their computer off until that light goes out. This lets the
- controllers do write behind fairly safely. (But you can still loose
- power, so this isn't risk free.) They also do crude read a heads by
- prereading entire tracks.
-
- DOS also runs in real mode and real mode can only access 640K of
- memory. This mean that a disk cache can be real helpful.
- Unfortunately, to do a software based disk cache, the cpu has to be
- switched into protected mode in order to access memory beyond the 640K
- boundary and then you have to switch back into real mode. Intel,
- however forgot to make it easy to switch back to real mode. All in
- all, this switching back and forth ends up being real expensive. This
- _might_ be more expensive than just using a caching controller, I
- don't know.
-
- So, it is possible that if you configure DOS to not use a cache, and
- get a caching controller, then you might be a head. I really don't
- know much about this area. I have not done any real timings of this.
-
- *** So, when would you ever want to buy a caching controller?
-
- The answer is not too often, but there are a few cases that I can
- think of:
-
- * You have filled up all your SIMM slots on your motherboard and in
- order to add more memory you would have to throw some out. This is
- a real shaky reason. You can always sell your old memory, or move
- it to another computer. The jump from 4 1MB SIMMs to 4 4MB SIMMs is
- large, but you will be much better off in the long run with more
- main memory.
-
- * You have maxed out your memory and you need it all for programs and
- data. If you can't put any more memory on the mother board, then
- you don't have many choices.
-
- * If you have a bunch of slow (100ns-120ns) memory left over from say
- a 286 or something and you can't use it on your motherboard because
- it is too slow, then maybe adding it to a caching controller
- will help. Be careful however, if your hit rates on the caching
- controller are too low, then you may be just adding overhead without
- getting any benefits.
-
- * If you are stuck with a bad OS because that's what your applications
- run on, then you might be better off with a caching controller.
-
- *** What about those disk drives that come with caches, are they bad too?
-
- Don't confuse caching disk controllers with cache on disk drives. The
- latter is actually useful. The little cpu on the disk drive has to
- read every byte that comes off the disk in order to see when the
- sector that you are interested in has come under the heads and to do
- any error detection and correction. The disk also has to have buffers
- in case the bus is busy, and to sync up the speeds of the bus and the
- heads.
-
- Since all this data is going though the cpu on disk drive and you have
- to have a buffer anyway, just making the buffer larger and saving the
- entire track is an easy win. Saving a couple of the most frequent
- tracks is also a win.
-
- Most of these caches on the disk drives are fairly small (64k-256k),
- and a single memory chip will give you about that amount of memory
- anyway, so you aren't wasting many resources. This also allows the OS
- to always assume that interleaving is not necessary to get full disk
- throughput, even if it does a fair amount of processing between disk
- requests.
-
- Q) 3.4 Do IDE controllers use DMA?
-
- No, they do not. This is a rumor that keeps popping up. This may
- change on the next revision of the standard.
-
- Q) 3.5 *How do I get an MFM/RLL/ESDI & IDE drive to coexist with each other?
-
- Q) 3.6 Why won't my two IDE drives work together?
-
- [From: jruchak@mtmis1.mis.semi.harris.com (John Anthony Ruchak)]
-
- Assuming that the drives are attached to the same controller and they
- work properly when attached one-at-a-time, you probably don't have
- them configured properly for Master/Slave operation.
-
- When operating 2 IDE drives, one must be designated as "Master" and
- the other as "Slave." There are jumpers on every IDE drive to
- configure this. Check your hard drive manuals for the jumper settings
- for your drives. In general, it doesn't matter which is which - just
- pick one as master, and make the other slave.
-
- In your CMOS configuration, Drive 1 should have the parameters (heads,
- cylinders, etc.) that match the drive you set as "Master" and Drive
- 2's parameters should match those of the "slave" drive. In operation,
- the Master will appear as drive C: and the slave as drive D:.
-
- Because not all hard drive manufacturers follow the IDE specifications
- closely enough, drives from 2 different manufacturers may not work well
- together. In this case, changing master -> slave and slave -> master
- (along with the appropriate CMOS changes) may help. If it doesn't,
- then trying two drives from the SAME manufacturer is the only avenue
- you have left.
-
- Q) 3.7 *Which is better, VLB or ISA IDE?
-
- Q) 3.8 How do I install a second controller?
-
- [From: strople@ug.cs.dal.ca (PAUL LESLIE STROPLE)]
-
- The following should solve about 95% (9.5?) of second controller
- problems, if only to tell you it can't be done!
-
- Generic Second Controller Installation:
-
- 1) Normally the MFM/IDE/RLL controller is set up as the primary, and
- the ESDI/SCSI as the secondary; One reason for this is because the
- ESDI/SCSI controller cards are usually more flexible in their set up
- and secondly this method seems to work (probably due to reason one).
-
- 2) Your primary controller is set up using all the normal defaults:
- - Floppy at primary address(3F0-3F7).
- - Hard disk enabled, at primary addresses (1F0-1F7),
- BIOS address C800 and interrupt 14.
-
- 3) Your secondary controller is set up as:
- - Floppy drives disabled
- - Hard disk controller enabled, secondary address(170- 177) and
- interrupt 15.
- - NOTE: onboard bios set to D400, or D800 can be used, if there is a
- conflict.
-
- 4) Computer BIOS Setup:
- - Any drive(s) on the primary controller (MFM/IDE), should be
- entered in the BIOS setup as usual.
- - You DO NOT enter the drive types for the hard disks on the
- secondary controller, even if there are only two drives in the entire
- system i.e., if one drive on each controller you only enter the drive
- type of the hard disk on the primary controller -- the 2nd drive type
- is left as not installed (0).
-
- Operating System:
-
- If you do the above steps you now have the hardware setup correctly;
- your only other problem may be with the operating system.
-
- Different OSs handle secondary controllers differently; as well,
- different controllers handles same OSs differently (scared yet?).
-
- For example: with DOS you may require a device driver (available from
- the manufacture or through third party companies, such as Ontrack
- Computer Systems -- more on Ontrack later). Some flavors of UNIX
- handle a mixture of controllers better than others (e.g., IA 5.4 had
- probs mixing ESDI and SCSI controllers under certain conditions).
-
- Procedure:
-
- You should verify that your secondary controller, and associated hard
- drives, are working properly (you can try this by installing it as the
- primary system -- removing existing system first!). Follow above
- steps 1 to 4, pray, and turn on system! If it still won't work you may
- need additional drivers. First check with the supplier or manufacture
- (I know, for example, a DTC ESDI controller comes with the DOS drivers
- included, and it works perfectly).
-
- I am not sure of operating systems supported by Ontrack Data Systems.
- I know that their DOS driver can assist secondary controllers, even
- allowing two IDEs to co-exist. Likewise, the drivers can also install
- virtually any drive, regardless of what is supported by the BIOS.
-
- BIG NOTE: The features required in a secondary controller a normally
- not found on a $30.00 IDE controller. The best thing to do it, if
- possible, is to get a guarantee from the supplier/manufacture that if
- it doesn't work (and they can't make it) then they will take it back.
-
- Ontrack supplies a complete range of hard disk products and services
- -- from driver software, data recovery services, to media and data
- conversions (including tape backups). The product I know them from is
- DiskManager.
-
- Disk Manager is a utility for hard disk management. It will allow you
- to setup and install virtually any hard disk, regardless of disk's
- layout and BIOS options available. Disk Manager (version greater than
- 5.2.X, or there abouts) includes a driver for co-resident controllers.
- For driver to work the co-res board must be able to hit the above
- addresses and must be WD1003 AT command set compatible (this includes
- most IDE and ESDI boards).
-
- DM contains a number of features, including full diagnostics. You may
- not need to know the disk's geometry, as there are numerous layouts
- stored internally. All you need to do is select the correct model and
- DM does the rest.
-
- To contact Ontrack: U.S. (800)-872-2599; UK 0800-24 39 96 this is
- either an address or phone number! outside U.K. (but NOT U.S.)
- 44-81-974 5522
-
- Q) 3.9 Which is better, SCSI or IDE?
-
- [From: ralf@wpi.wpi.edu (Ralph Valentino)]
-
- IDE vs SCSI
-
- Non-issues:
- 1) SCSI and IDE devices cost approximately the same for the same
- features (size, speed, access time). Shop around for good prices.
-
- Advantages of IDE:
- 1) faster response time (low request overhead)
- 2) hard drive interface is compatible with RLL/MFM/ESDI: any driver
- for one (including the main system BIOS) will run the other.
- 3) IDE controllers are considerably cheaper ($150 and up) than SCSI
- host adapters.
- 4) Will always be the boot device when mixed with SCSI.
-
- Advantages of SCSI:
- 1) Supports up to 7 devices per host adapter. This saves slots,
- IRQ's, DMA channels and, as you add deviceds, money.
- 2) Supports different types of devices simultaneously the same host
- adapter (hard drives, tape drives, CDROMs, scanners, etc).
- 3) SCSI devices will work in other systems as well (Mac, Sparc, and
- countless other workstations and mainframes). If you change platforms
- in the future, you will still be able to use your SCSI devices.
- 4) Automatically configures device type, geometry (size), speed and
- even manufacturer/model number(SCSI-2). No need to look up CMOS
- settings.
- 5) Busmastering DMA (available in all but a few cheap SCSI host
- adapters) decreases amount of CPU time required to do I/O, leaving
- more time to work on other tasks (in multitasking OS's only).
- 6) Software portability - drivers are written for the host adapter,
- not the specific device. That is, if you have a CDROM driver for your
- host adapter, you can purchase any brand or speed SCSI CDROM drive and
- it will work in your system.
- 7) Will coexist with any other type of controller (IDE/RLL/MFM/ESDI)
- or host adapter (other SCSI cards) without any special tricks. SCSI
- host adapters do not take up one of the two available hard drive
- controller port addresses.
- 8) greater bandwidth utilization (higher throughput) with multiple
- devices. Supports pending requests, which allows the system to
- overlap requests to multiple devices so that one device can be seeking
- while the second is returning data.
- 9) Ability to "share" devices between machines by connecting them to
- the same SCSI bus. (note: this is considerably more difficult to do
- than it sounds).
- 10) Bridges are available to hook RLL and ESDI drives to your SCSI host
- adapter. (note: these tend to be prohibitively expensive, though).
-
- Warnings:
- 1) With otherwise equal drives, IDE will perform better in DOS due to
- low command overhead. SCSI, however, will perform better in
- multitasking OS's (OS/2, Unix, NT, etc). If you see speed comparisons
- (benchmarks), make sure you know what OS they were run under.
- 2) Most benchmarks only test one aspect of your system at a time, not
- the effect various aspects have on each other. For instance, an IDE
- drive may get faster throughput but hurt CPU performance during the
- transfer, so your system may actually run slower. Similar confusions
- arise when comparing VLB and EISA host adapters.
- 3) When comparing two systems, keep in mind that CPU, memory, cache,
- and bus speed/type will all effect disk performance. If someone gets
- great I/O performance with a particular controller/drive combination
- on his Pentium, you should not expect your 386SX-25 to get such I/O
- performance even with the exact same controller/drive combination.
- 4) Similarly sized or even priced drives may not perform equally, even
- if they're made by the same manufacturer. If you're going to compare
- two drives, make sure they have the exact same model number. (IDE
- drives usually have an 'A' and SCSI drives usually have an 'S'
- appended to their model number).
-
- Q) 3.10 Can MFM/RLL/ESDI/IDE and SCSI coexist?
-
- The PC is limited to two drive controllers total. SCSI, however, is a
- "host adapter" and not a drive controller. To the rest of your
- system, it appears more like an ethernet card than a drive controller.
- For this reason, SCSI will always be able to coexist with any type
- dive controller. The main drawback here is that on most systems, you
- must boot off a disk on the primary drive controller, if you have one.
- That means if you have SCSI and IDE in your system, for example, you
- can not directly boot from the SCSI drive. There are various ways to
- get around this limitation, including the use of a boot manager.
-
- Q) 3.11 What's the difference between SCSI and SCSI-2? Are they compatible?
-
- The main difference between SCSI and SCSI-2 are some new minor
- features that the average person will never notice. Both run at a
- maximum 5M/s. (note: Fast and Wide SCSI-2 will potentially run at
- faster rates). All versions of SCSI will work together. On power up,
- the SCSI host adapter and each device (separately) determine the best
- command set the speed that each is capable of. For more information
- on this, refer to the comp.periphs.scsi FAQ.
-
- Q) 3.12 Can I share SCSI devices between computers?
-
- There are two ways to share SCSI devices. The first is removing the
- device from one SCSI host adapter and placing it on a second. This
- will always work if the power is off and will usually work with the
- power on, but for it to be guaranteed to work with the power on, your
- host adapter must be able to support "hot swaps" - the ability to
- recover from any errors the removal/addition might cause on the SCSI
- bus. This ability is most common in RAID systems.
-
- The second way to share SCSI devices is by connecting two SCSI busses
- together. This is theoretically possible, but difficult in practice,
- especially when disk drives are on the same SCSI chain. There are a
- number of resource reservation issues which must be resolved in the
- OS, including disk caching. Don't expect it to 'just work'.
-
- Q) 3.13 How do I swap A: and B:
-
- [From: rgeens@wins.uia.ac.be (Ronald Geens)]
-
- To swap A: and B: drives :
- 1) open up your machine to see if look at the cable that interconnects
- the 2 drives.
- 2) if the cable is twisted, there is no problem, just switch the
- connectors from 1 drive to the other.And change the bios-setup.
- 3) if the cable isn't twisted (which is very,very rare), it's a little
- harder: leave the cables as they are, but change the jumpers on the
- drive. (this sounds a lot tougher, but it can usually be done without
- to much hassle. When the cable connecting the 2 drives is just a flat
- one (like the harddisk cable) then you must play with the jumpers on
- the drives: Most of the time, there is a jumper with 4 pins, with the
- following layout:
- _
- |1|
- |2*3|
- ---
-
- Where the * is the 4th unnumbered pin. Normally the A: drive will have a
- jumper on pin 2 & 4 and the B: drive on 1 & 4. Just change these jumpers
- around, (i.e. new A: 2&4, new B: 1&4) and change the BIOS configuration.
- 4) Don't panic if it doesn't work, just make sure all cables are
- conected properly and if that doesn't work just restore everything to
- its old state.
- PS. By twisted cable, I mean that between the A: and B: drive, a few
- wires of the flat cable are turned around.
-
- [From: sward+@CMU.EDU (David Reeve Sward)]
-
- I have found two ways to do this: I originally switched their
- positions on the cable attached to the controller, and changed the
- BIOS to reflect this. I recently got a gsi model 21 controller for my
- IDE drive, and this controller allows you to specify which drive is A:
- and B: in software (it lights the LEDs in turn and asks which is A:
- and which is B:). This did not require a cable change (but I still
- changed by BIOS).
-
- Q) 3.14 What is a 16550 and do I need one?
-
- The 16550 is a UART with two 16 byte FIFOs. A UART is the part of a
- serial port that takes byte-wide (characters) data and converts it to
- bit-wide (serial) data, and visa versa. The FIFO is a buffer which
- can hold characters until the CPU is ready to remove it or until the
- serial line is ready to transmit it. The 'normal' UART in the PC (the
- 8250 or 16450) only has 1-byte FIFOs. The additional 15 bytes can be
- useful when the CPU is busy doing other things - if the CPU isn't able
- to remove data fast enough, it will be lost.
-
- A very important thing to note is that under DOS, the CPU doesn't have
- anything else to do, so the 16550 is wasted. Only under multitasking
- operating systems does it really become useful. The 16550 will *not*
- make your file transfers any faster, it will only prevent data from
- being lost and relieve your CPU of some overhead. If you notice
- system performance dropping like a rock when file transfers are
- occurring, a 16550 may be helpful. If you see re-transmissions (bad
- packets) or "FIFO overrun's" during file transfers under a
- multitasking OS, try the same thing under DOS - if the errors go away,
- then chances are a 16550 will be useful. If they remain, then your
- problem is likely to be elsewhere.
-
- Q) 3.15 *Are there any >4 serial port cards?
-
- Q) 3.16 Should I buy an internal or external modem?
-
- [From: arnoud@ijssel.hacktic.nl (Arnoud Martens)]
-
- While low speed modems are often only produced as an internal PC card,
- most modem manufacturers provide two versions of their higher speed
- modems:
-
- 1: internal ISA bus card, specially designed to work with the
- standard PC bus. You just plug it in and configure it to use on
- port.
-
- 2: external modem that has to be connected to the serial ports of
- your PC (com 1-4), using a serial RS232 cable.
-
- In most cases the functionality of these two is equal. There are
- however some differences in using, maintaining and buying these
- modems. It is very difficult to give an definite answer as to which one
- is better, it completely depends on your own situation. Some of the
- points that are in favor of an external modem are:
-
- * It has lights showing the status of the connection, this can be
- useful in those (rare) cases that you have problems with the
- connection.
-
- * It can be used on a wide range of systems. External modems
- are connected using a RS232 cable, a standard that most computer
- systems support. So you can as easily use your external modem
- on a Mac, Amiga or Unix box as on your PC.
-
- * It doesn't consume power inside the PC (it uses a normal net
- adapter), and doesn't produce any heat inside your PC.
-
- On the other hand the internal modem has also a couple of advantages
- compared to an external modem:
-
- * It is always cheaper, Somewhere in the order of 10% less compared
- to the same external modem.
-
- * It doesn't need special serial hardware since it has already
- been integrated on the board, which will make it even more
- cheaper.
-
- So basically if portability of your modem is an issue, you are better
- of with an external modem. But if you only intend to use the modem
- with your PC and don't have any power problems, an internal modem is
- the best choice.
-
- Q) 3.17 What do all of the modem terms mean?
-
- [From: arnoud@ijssel.hacktic.nl (Arnoud Martens)]
-
- A modem (MOdulator-DEModulator) is a device capable of converting digital
- data from your computer into an analog signal that is suitable for
- transmission over low band width telephone lines. A modem thus makes it
- possible to connect two computers over a telephone line and exchange data
- between them.
-
- Basically a modem picks up the phone, and dails a number. A modem on
- the other side will pick up the phone and the two modems will
- negotiate which protocol to use. When they agree the actual
- transmission of data can begin.
-
- The major feature of a modem is the speed that it can achieve
- connecting to other modems. This speed is often expressed in baud or
- bits per second. The first is a feature of the line and specifies how
- much of the bandwidth of the phone channel is used and is fixed to
- 2400 baud. A baud is defined as the number of lines changes per
- second. Bits per second is the actual amount of data transmitted in
- one second. Most modems are capable of sending more than one bit per
- line transition by using very intelligent signal modulation
- techniques. So the bps can be eight times higher compared to trhe baud
- rate.
-
- The modulation techniques that a modem uses are standarized by the
- ITU-T ( former CCITT), so that modems of different brands can connect
- to each other as they use the same modulation schemes. These standards
- are often incorporated in a protocol definition that is referred to by
- the letter V followed by a number. The most common protocols are:
-
- V21: (300 baud)
- V22bis: (2400 baud)
- V32: (9600 baud)
- V32bis: (14400 baud)
-
- A modem is often advertised only by its fastest protocol, most of these
- modems "speak" slower protocols as well.
-
- There are also standards on using data compression by the modem, such as MNP5
- and V42bis, and error control protocols (V42 and MNP4). These standards can
- reduce the transmitted data by a factor four, by using advanced compression
- techniques.
-
- To give you an idea a how fast fast is in modem technology: V32bis transmits
- somewhat like 1600 characters per second (that is ~33% of 1 page of
- text). Transferring a file of 1Mb takes about 12 minutes. Using V42bis can
- speed up transmission to 4000 characters per second for uncompressed data.
-
- Apart from these standardized protocols there are also faster protocols which
- are supported by some modem manufacturers. But remember anything faster than
- 14k4 is *not yet* standarized, and often different manufacturers use their
- own modulation scheme that allows only their own modems communicate at that
- speed. The most common high speed protocols are:
-
- V32 terbo (19200 baud)
- V34 (28800 baud) or Vfast.
-
- The standard for V34 is being worked on, it will be released somewhere in
- 1994. Some modem manufacturers already sell modems with the (prelimenary) V34
- standard. If you are serious about buying a fast modem, upgradability to this
- standard should be provided by the manufacturer.
-
- When you use your modem it is important to differentiate between command
- status and connect status of your modem. When you are connected to an another
- modem everything you send to the modem, will be transmitted to the other
- modem. In command mode everything you type will be recieved and interpreted
- by the modem. Command mode allows you to change the default settings for
- youyr modem.
-
- In command mode it is likely that your modem will respond to the Hayes AT
- command set. "AT commands" all have prefix AT, and can be used to change the
- (default) settings of your modem. To check if your modem works, fire up a
- terminal program (such as kermit), connect to your modem (in kermit c
- [ENTER]) and issue AT [ENTER], if your modem works it should respond with
- OK. For a list of all "AT commands" see the manual of your modem, as most AT
- commands are modem specific.
-
- If you buy a fax-modem, you should pay attention to a couple of things. First
- the modem must support Class 2 fax commands, furthermore automatic fax mode
- selection is a big pro. That means if you receive a call the modem is capable
- of detecting a fax message or a modem connection and act properly (start up a
- fax receiving program or spawn something like a login process on the
- connection).
-
- Finally there is no best modem to get, brands and qualities change very fast,
- as do the prices. If you are interested in buying one, subscribe to the
- newsgroup comp.dcom.modems, most postings in this group are very brand
- oriented and you will recognize fast enough which users are satisfied over
- their modems and which are not.
-
- Q) 3.18 What kinds of sound cards are avalable?
-
- This is covered in the comp.sys.ibm.pc.soundcard FAQ, archive name:
- PCsoundcard/soundcard-faq. Please refer to this document for more
- information.
-
- Q) 3.19 Where can I find EISA/VLB sound and IO cards?
-
- Chances are that you won't be able to find them anywhere, and if you
- do, they won't be worth the money. Sound and IO cards have very low
- bandwidth requirements, over 10 times lower than the ISA bandwidth and
- over 60 times lower than the EISA bandwidth. For this reason, there
- is no advantage in placing them on the more expensive EISA/VLB cards
- when the less expensive ISA will more than suffice, especially
- considering than all ISA cards will work in an EISA/VLB slot.
-
- Q) 3.20 +How does the keyboard interface work?
-
-
- [From: jhallen@world.std.com (Joseph H Allen)]
-
- The IBM keyboard is connected to the computer through a serial interface
- similar to a COM port. When you press a key, the keyboard sends a
- "scan-code" for that key to the computer. When you release the key, the
- keyboard sends a release code to the computer. If you hold down one key and
- press and release another key, the computer will receive the scan-code for
- the held key and a scan and release code for the other key. Since the
- release code for the held key was not received, the computer knows that the
- held key was down while the other key was pressed. In this way, the
- computer can handle the Shift, Alt and Ctrl keys (and any key could work
- like a shift key, since all keys work alike). The ROM BIOS in the computer
- buffers the data from the keyboard, translates the scan-codes to ASCII and
- handles the operation of the shift and lock keys. The keyboard itself also
- has a small buffer and there is hardware flow-control for preventing
- overruns. All of this seems simple and quite elegant, but by the time we
- get to the AT keyboard the details of the implementation are so complicated
- as to ruin an otherwise ideal keyboard.
-
- The XT keyboard's interface almost captures the above elegance (indeed it is
- the only elegant thing about the XT, IMHO). The interface uses a 5-pin DIN
- connector with these signal assignments:
-
- 1 CLK/CTS (open-collector)
- 2 RxD
- 3 RESET
- 4 GND
- 5 +5V
-
- When the keyboard has a byte to send to the computer, it shifts 9 bits out
- to the data line (RxD) with nine clock pulses on the CLK line. The data
- format is 1 start bit, followed by 8 data bits. The baud rate is roughly
- 2000 bits per second and is not precisely defined. Once a byte is
- completely transmitted, the computer holds the Clear-To-Send (CTS) line low
- to prevent the keyboard from sending any more bytes until the keyboard
- interrupt handler reads the current one. Usually a simple 9-bit clearable
- TTL shift register is used to receive keyboard data. The 9th bit of the
- shift register is used to drive an open-collector buffer connected to the
- CTS line. When the start-bit gets all of the way through the shift
- register, it holds the CTS line low itself. Once the CPU reads the
- assembled byte, it has only to clear the shift register to release the CTS
- line and allow another byte to be received. Three TTL chips or a single PAL
- can implement an entire XT keyboard interface.
-
- The data bytes which the XT sends are also simple. Codes 0-127 are the
- scan-codes. Codes 128-255 are the release codes- they're the same as the
- scan codes, but with the high bit set. The XT keyboard has only 84 keys, so
- not all of the scan-codes are used.
-
- The only problems with the XT keyboard are the lock-status lights
- (Caps-lock, Scroll-lock and Num-lock) and the key repeat mechanism. The
- lock-status lights can get out of sync with the computer's idea of which
- lock keys are activated, but this only happens if someone resets the
- keyboard by unplugging it temporarily. When you hold a key down long
- enough, the keyboard starts repeating the scan-code for that key. The
- release code is still only transmitted once, when the key is released. The
- problem here is that the delay to the start of the repeats and the repeat
- rate were made too slow. Of course, the keyboard really doesn't have to
- handle repeat at all, since the computer knows when keys are pressed and
- released and has a timer itself. Old XT keyboard TSRs allowed you to adjust
- the repeat delay and rate by duplicating the key repeat mechanism in the
- computer.
-
- Once IBM found that it had a nearly perfect keyboard it, of course, decided
- that it had to be almost completely redesigned for the AT. The keyboard
- didn't have to be redesigned- there were enough extra scan-codes for the
- AT's 101 key keyboard and the repeat mechanism could simply have been moved
- to the BIOS. But no, they had to redesign everything. Sigh.
-
- The AT uses a 5-pin DIN and the PS/2 uses a smaller connector with the same
- signals:
-
- 1 CLK/CTS (open-collector)
- 2 RxD/TxD/RTS (open-collector)
- 3 Not connected or Reset
- 4 GND
- 5 +5V
-
- Now the interface is bi-directional. When the computer wants to send a byte
- to the keyboard, it asserts RTS and releases CTS. If you're lucky, the
- keyboard isn't deciding to transmit at the same time and it responds by
- giving 10 clock pulses (at about 10000 baud) on the CLK line. The computer
- shifts a frame out on TxD on rising clock edges. The frame format is now 1
- start bit, 8 data bits and 1 odd parity bit. The keyboard takes RTS being
- held low as the first start bit, and the first data bit should be sent on
- TxD after the first clock edge is received. Yes, now you need a full UART
- for the keyboard interface since you have to both transmit and receive and
- generate and check parity (but it's still not RS-232- that would have been
- too logical). Why do you need parity checking on a three foot long keyboard
- cable? Because collisions can occur since the lines are so overloaded with
- signals with different meanings and parity provides the means for detecting
- these collisions.
-
- The AT documentation says that pin 3 is "reserved", so the keyboard has to
- provide its own reset. But on the original AT, pin 3 was still Reset and
- IBM's own keyboards at that time needed Reset (original AT keyboards won't
- work on some old clones because of this). Don't ask me... I don't
- understand why they did this.
-
- The protocol on the keyboard interface is now much more complicated. These
- bytes are defined:
-
- Commands
-
- ED <byte> Set leds depending on byte
- bit 0 is Scroll lock
- bit 1 is Num lock
- bit 2 is Caps lock
-
- EE Echo EE (for testing?)
- F0 <mode> Select mode 1, 2 or 3
- F2 Send keyboard I.D.
- F3 <byte> Set repeat delay and rate
- byte is: 0ddbbaaa
- delay is (dd+1)*250 msec
- rate is (8+aaa)*2^bb*4 msec
-
- F4 Clear buffer
- F5 Restore default settings and wait for enable
- F6 Restore default settings
- FA Acknowledge
- FE Error- please retransmit
- FF Reset keyboard
-
- Status returns
-
- 00 Buffer overflow
- AA Self-test passed
- F0 <scan-code> Release code
- FA Acknowledge last command
- FD Self-test failed
- FC Self-test failed
- FE Last command in error; re-send
- E0 scan/release code Extended keys in Mode 2
-
- The computer and keyboard must acknowledge each command and key code with
- either FA if there was no error, or FE if the last command/key-code should
- be re-sent. There are three modes of operation for the keyboard, depending
- on which scan code assignments you want (these can often be set by a switch
- on the back of keyboard, except that if mode 1 is selected from the switch,
- the protocol is eliminated an the keyboard works exactly like an original XT
- keyboard- newer keyboards only support modes 1 and 3). In mode 1, the
- keyboard gives XT scan-codes. The keyboard handles the cursor keypad (which
- didn't exist on the XT) by simulating pressing or releasing a shift key
- (depending on whether shift or num-lock are pressed) and sending codes from
- the numeric keypad. Mode 2 works like mode 1, except that when the keyboard
- does the weird stuff with the numeric keypad it prefixes everything with E0
- and the release codes are the scan-codes prefixed with F0. In mode 3, each
- key gets a unique code and the release codes work as in mode 2: the release
- are the scan-codes prefixed by F0.
-
- When the AT keyboard is first reset it's supposed to send an AA if its
- self-test passed or FD or FC if it failed. But before it does this, it
- sends a continual stream of AAs with the parity incorrect. Once the
- computer sends an FE to indicate that there is a parity error, the keyboard
- stops sending bad AAs and sends a correct AA or an FD or FC. This sounds
- like someone made a quick fix in the keyboard firmware for mis-matched reset
- timing (the keyboard always finishes resetting before the computer so the
- computer could miss the AA/FD/FC).
-
-
- Q) 3.21 +Can I fake a keyboard so my computer will boot without it?
-
-
- [From: jhallen@world.std.com (Joseph H Allen)]
-
- () The IBM Keyboard - how do you use a computer without a keyboard?
-
- Sometimes a PC needs to be set up as a "turn-key" system with no keyboard
- for security reasons, or simply because the application doesn't need a
- keyboard. This causes a dead-lock problem when the system is booting: The
- BIOS will detect that there is no keyboard and display the message "keyboard
- failure - press F1 to continue," and the system becomes stuck.
-
- There is usually a BIOS set-up option for disabling the keyboard test.
- Check the manual for your motherboard. If your BIOS does not have this
- option, you're essentially screwed because there's no simple solution. You
- can't wire the DIN to fake the existence of a keyboard since the BIOS checks
- for a self-test result code generated by the keyboard. In fact, you would
- have to implement a small protocol (byte-by-byte handshaking and ACK/NAK) to
- simulate a keyboard up to its self test. It's conceivable that someone could
- make a DIN connector with a small microcontroller in it to do this, but I
- have never seen such a thing. Another solution is to replace your BIOS with
- one which has the keyboard test disable option. However, you have to find
- one which matches your motherboard.
-
-
- S) 4.0 Storage/Retrieval Devices
-
- Q) 4.1 Why do I lose x Meg on my hard drive?
-
- [From: Mike Long <mike.long@analog.com>]
-
- The problem here is that there are two different measures of hard
- drive storage, both called megabytes. Computer hardware works on the
- basis that one megabyte equals 2^20, or 1048576 bytes. Hard drive
- manufacturers, on the other hand, use a megabyte that has 1000000
- bytes, because it makes the drive looks larger. When buying a hard
- drive, you should expect to lose almost 5% of what the manufacturer
- claims the drive size to be.
-
- The manufacturers are not totally at fault. The first track of the
- drive is used for the partition table and master boot record. The
- amount of data lost here depends on your drive parameters; usually
- there are between 32 and 64 sectors (512 bytes/sector) on this first
- track, so you lose between 16384 and 32768 bytes that way.
-
- Additional space is taken up by two hidden files on your boot drive.
- If you are running MS-DOS, these files are IO.SYS and MSDOS.SYS. If
- you are running PC-DOS, the names are IBMIO.SYS and IBMDOS.SYS (?).
-
- [From: ralf@wpi.wpi.edu (Ralph Valentino)]
-
- Many drives these days advertise unformatted capacity. The actual
- formatted capacity may be significantly lower than this as space is
- taken up marking tracks, sectors, CRC's, etc. Exactly how much lower
- depends on the the size of the sectors. For instance, placing 1k
- sectors on the disk instead of the usual 512 byte ones may slightly
- increase the usable storage space on the disk. Note, however, that
- many OS's insist you stick to the 512 byte sectors so this option is
- best left alone.
-
- A large number of drives also do auto-mapping of bad sectors; when a
- sector goes bad, it will automatically use a spare it kept aside
- during the format. This is very handy as the OS never needs to deal
- with the problem and some OS's, like DOS, will mark a whole cluster
- bad when a single sector goes bad. These spare sectors, as many as
- one per track, remain hidden from the OS but still take up space on
- your hard drive.
-
- When you get to drives larger than 1.0 gig (SCSI), many host adapter
- BIOS's can not deal with this as the BIOS was never designed to handle
- more than 1024 cylinders, 64 heads, and 32 sectors per track. (1024 *
- 64 * 32 * 512bytes/sec = 1.0 gig). Luckily, some OS's (like OS/2)
- ignore the BIOS all together and read the actual geometry from the
- disk itself. If, however, you're not using such an OS and you notice
- that you only have 1.0 gig available, you may want to check with the
- manufacturer of your SCSI host adapter to see if a newer BIOS is
- available.
-
- Q) 4.2 *Should I get an IDE/floppy/SCSI/parallel port tape drive?
- Q) 4.3 I have two floppies. Can I add a floppy based tape drive?
-
- [From: herbst@techunix.technion.ac.il (Herbst OMR)]
-
- It depends. On all modern tape drives: yes. Some old tape drives
- cannot do this (my old Jumbo). If you have one of these, you will have
- to buy either a 4-floppy controller or a dedicated tape controller.
-
- Q) 4.4 How fast is a tape drive? Will a dedicated controller improve this?
-
- [From: herbst@techunix.technion.ac.il (Herbst OMR)]
-
- The tape connected through a floppy interface is limited to the floppy
- speed. On ATs 500Kbit/S. On old XT 250Kbit/S. With card support for
- 2.88MB floppy, 1Mbit/S. Many of the newer cards support this transfer
- rate.
-
- If the card operate at 500Kbit/S, a dedicated controller card will
- speed up the tape by a factor of two. In many cases, those cards do
- hardware compression, helping even more.
-
- Q) 4.5 What is QIC80, QIC40?
-
- [From: herbst@techunix.technion.ac.il (Herbst OMR)]
-
- QIC stands for Quarter-Inch Cartridge. QIC80 is the standard for 80MB
- tapes, QIC40 for 40MB tapes. Both standard allows for extended length
- cassettes of 300ft which gives 120MB and 60MB respectively.
-
- Q) 4.6 How come I can't fit as much stuff on my tape drive as they claim?
-
- Most tape drives these days advertise capacity with an expected
- compression ratio of 2:1. If you are backing up compressed files
- (.Z,.ZIP, .ARC, .JPEG, and so forth) then the drive's own compression
- scheme will not be as effective. For these cases, the actual capacity
- of the tape will be closer to the "uncompressed" capacity.
-
- A table from herbst@techunix.technion.ac.il (Herbst OMR) shows:
-
- stated capacity standard tape length # tracks
-
- 80MB QIC40 200ft (normal) 15
- 120MB QIC40 300ft (extended) 15
- 160MB (rarely) QIC80 200ft 28
- 250MB QIC80 300ft 28
-
- For all the recording density is 12500 ftpi; max tape speed is 90 ips.
-
- A second reason is that some tapes assume you will be taking full
- advantage of their "streamers". Streaming collects a number of tape
- blocks and writes them all at once, preventing the need for backing up
- the tape after each block. This positions the blocks closer together
- on the tape. If your backup program is slow, some streamers won't be
- quite as effective. If you hear the tape drive motor backing up the
- tape alot on writes, this could be the case.
-
- Q) 4.7 Are Colorado/Conner/Archive/... tapes compatible with each other?
-
- [From: herbst@techunix.technion.ac.il (Herbst OMR)]
-
- If you use the same software: Yes. If you want to use different
- software, then turn compression off. Compression done in software on
- those drives is not compatible.
-
- Q) 4.8 How does the drive/software know how long the tape is?
-
- [From: herbst@techunix.technion.ac.il (Herbst OMR)]
-
- The magnetic tape has holes in it. Inside the cassette enclosure there
- is a small mirror. The drive sends an IR beam through it. Near the end
- of tape the drive receives it. If the IR receiver is dusted, the drive
- may 'reel off' the cassette.
-
- Q) 4.9 What are all those QICs?
-
- [From: herbst@techunix.technion.ac.il (Herbst OMR)]
-
- (Thanks to Karl-Peter Huestegge and Jan Christiaan van Winkel)
- QIC-11 is not an Industry Standard and there exist some incompatible
- versions.
-
- Standard Capacity Tracks Speed Rec-density Flux-Trans Cartridges
- ----------------------------------------------------------------------------
- QIC-11 15/30MB (300ft) 4/9 90ips
- 20/40MB (450ft) 4/9 90ips 6400ftpi DC300XL
- 10000ftpi DC300XLP
- 27/60MB (600ft) 4/9 90ips 10000ftpi DC600A
-
- QIC-24 45MB (450ft/137m) 9 90ips 8000bpi 10000ftpi
- 55MB (555ft/169m) 9 90ips 8000bpi 10000ftpi
- 60MB (600ft/183m) 9 90ips 8000bpi 10000ftpi DC600A
-
- QIC-120 125MB (600ft/183m) 15 72ips 10000bpi 12500ftpi DC600A
-
- QIC-150 155MB (600ft/183m) 18 72ips 10000bpi 12500ftpi DC600XTD
- DC6150
- QIC-150 250MB (1000ft/305m) 18 72ips 10000bpi 12500ftpi
-
- QIC-320 320MB (600ft/183m) 26 72ips 16000bpi 20000ftpi DC6320
-
- QIC-525 525MB (1000ft/305m) 26 72ips 16000bpi 20000ftpi DC6525
-
- * QIC-1000 1000MB (760ft)
-
- * QIC-2GB
-
- * QIC-10GB
-
- Q) 4.10 Which QICs are read/write compatible?
-
- [From: herbst@techunix.technion.ac.il (Herbst OMR)]
-
- The left column should be read: "Tape drives designed for the QIC-???
- standard *should* be able to read/write the following Tape formats:"
-
- TAPE-DRIVES | Tape - Formats |
- designed for: | QIC-11 | QIC-24 | QIC-120 | QIC-150 | QIC-320 | QIC-525 |
- ----------------|--------|--------|---------|---------|---------|---------|
- QIC-11 | R W | | | | | |
- QIC-24 | R W | R W | R | | | |
- QIC-120 | R - | R - | R W | R | | |
- QIC-150 | R - | R - | R W | R W | | |
- QIC-320 | R - | R - | R W | R W | R W | ? ? |
- QIC-525 | R | R | R W | R W | R W | R W |
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-
- ===============
- Ralph Valentino (ralf@chpc.org) (ralf@wpi.wpi.edu)
- Hardware Engineer, Worcester Polytechnic Institute
- Center for High Performance Computing, Marlborough MA
-