
          +--------------------------------+
          | IDE HARD DRIVES in XT Machines |
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       [Copyright (c)1994 Paul Reid 71031,3603] 

        The original IBM PC had no hard drive, and the original 
IBM XT was a PC with more power to run a hard drive.  The 
original IBM XT hard drive was a 10 megabyte full height 5.25" 
MFM drive.  

        For many years various MFM and RLL drives were popular 
in XT's and clones, but now IDE drives are so common and so 
cheap that they must be considered. 

        The first problem is that the common ATA IDE drive is 
based on the 16-bit IBM AT bus interface, not the 8-bit XT 
interface.  The standard low cost IDE cards will not work in an 
XT.  

        Fortunately, special cards that have interfacing for IDE 
drives in 8-bit XT machines are now available. 

        The procedure is simple.  Buy a special 8-bit IDE 
controller, buy a drive, follow the instructions.  Usually you-
         1) Plug the cable into the drive and controller, plug 
        the controller into a bus slot, and plug the drive into 
        a power cable.  
         2) Start the XT with a bootable floppy disk.  
         3) Run FDISK and tell it you want to partition the whole 
        drive.  
         4) Reboot and run FORMAT C: /S to put the directory and 
        system files on the drive.  
        Ta-Da!  You're done. 

        But the two different 8-bit IDE controllers I've used 
gave very different results.  One was a real disappointment.

        An attempt to use a fast 130 megabyte drive with 
DoubleSpace disk compression with a slow IDE controller was 
hopelessly slow.  At first I thought it was dead.

        I have used the AccuLogic sIDE 1/16, but mine is an 
early card with the version 1.0 IDE BIOS.  The sIDE-1/16 asks 
the drive to auto-ID itself, this works on my ST-1144A desktop 
IDE drive but not my ST-9051A.  The sIDE-1/16 has a feature to 
over-ride the auto-ID feature, but it was buggy on early 
versions of the 1/16.  Also, my sIDE-1/16 is VERY SLOW, slower 
than an original XT controller even when used with a fast IDE 
drive, even when used in a fast machine.

        I have used the Silicon Valley ADP-50 IDE in XT card.  
This is a nice card.  With an old 40 megabyte IDE drive it runs 
5 times faster than an original XT drive.  With a newer drive in 
a 386 machine it went even faster.  It does not have the speed 
limit of the AccuLogic.  I like it a lot, both for XT use and 
for modest-speed use in the few AT's (286 and up) that don't 
like IDE drives.

        Of course, the AccuLogic sIDE is cheaper and more widely 
available than the ADP-50.  Prices on the sIDE run $30 to $50, 
on the ADP $50 to $70.  I think the sIDE is a poor investment.  
The extra $20 buys a LOT more speed. 

        An IDE drive which was formatted and works in another 
machine may not boot on these controllers.  Often IDE drives are 
run under "translation" parameters to avoid confusing AT-type 
BIOSes.  A drive that really has 40 sectors per track might be 
formatted with "17" sectors to satisfy a standard AT BIOS.  The 
number of tracks is also modified so the total comes out right.  
Many IDE drives will translate the logical "translation" 
parameters to physical parameters on the fly. Neither the sIDE 
or the ADP seems happy with translation, they want to use the 
drive's "true" physical parameters.  This means that DOS's first 
boot file will not be in the place pointed to by the old boot 
sector, written under translation parameters.  It may be 
necessary to FDISK and FORMAT to make the drive usable, and this 
makes the data unavailable. 
 
        It is unrealistic to run a large drive in a slow XT.  
DOS must read through those directory and file structures one 
byte at a time, and an 8088 is not too fast at these operations.  
A 40 meg drive is a nice size.  A 60 meg is about as big as an 
XT can run without feeling more sluggish than it already is.  
Use a 130 meg drive only if space is far more valuable than 
time.

        Disk compression is also a heavy load on an XT.  DOS 6's 
DoubleSpace makes the 8088 run so slow, I took it off right 
away.

        Many laptop computers have cute little 2.5 inch IDE 
drives.  I was told the 2.5 inch drives have funny connectors.  
They sure do, but you can buy an adapter to make it plug and 
mount like a 3.5 inch IDE drive for $15 & $5 shipping from  ICD, 
815-968-2228. 

 AUTHOR 
        All opinions, endorsements, and errors are my own.  
Comments, corrections, clarifications welcome! 

                                      Paul Reid 71031,3603 

