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VCF XT-IDE  -  Basics


Scope

The scope of this web page is the XT-IDE series of cards produced by the Vintage Computer Forums (VCF)
To date, there have been four releases: revision 1 (rev 1), revision 2 (rev 2), revision 3 (rev 3), and revision 4 (rev 4).

Some companies and individuals have designed products containing similar functionality.  Some of the information on this web page may not apply to those products.


Purpose / Description

It was long recognised that the MFM type hard drives associated (period correct) with the IBM XT (and clones), were becoming scarcer due to failure, and that replacement hard drive functionality was needed.

Although 8-bit IDE drives (and matching IDE cards) for the XT can still be sometimes found (on eBay, etc.), the quantity is very very low.

Members of the VCF decided to take advantage of the large nubers of 16-bit IDE drives (AT type of IDE) that exist (including CF cards and DOMs).  They designed a card, named the XT-IDE, which interfaces 16-bit IDE drives to the 8-bit expansion bus of the IBM XT.  Click here to see a diagram.   (Similar cards had already existed, an example being JDR's MCT-IDE-8.)

Like other XT-class hard disk controllers, the XT-IDE has what is known as a 'BIOS expansion ROM' (also known as a 'boot ROM').  That ROM contains software, the 'XTIDE Universal BIOS', software that was developed for the XT-IDE card.  Rather than using a ROM of type EPROM, the XT-IDE designers chose instead to wire the card for an EEPROM.  That enables the contents to be updated/changed via a DOS program.


Hardware

The card consists of two distinct hardware functionalities:
1.  IDE interface
2.  EEPROM and its support circuitry  ('boot ROM')  (which hosts the XTIDE Universal BIOS software)

From a hardware perspective, the two are completely seperate; two circuits put onto one card.  For example, you could build an XT-IDE card omitting the EEPROM and its supporting circuitry.  You would then put the XTIDE Universal BIOS into a ROM, placing that ROM into a (compatible) BIOS expansion ROM socket of a different card.

Revision 2 of the XT-IDE card is unique in that it has a third functionality (which is optional), a custom serial port (UART), so that if desired, a serial drive can be booted from.


Software

As stated before, the XT-IDE card contains the 'XTIDE Universal BIOS' software in its EEPROM.

A DOS program named XTIDECFG.COM is supplied to:
• Configure the XTIDE Universal BIOS
• Write the configured XTIDE Universal BIOS into the EEPROM


16-bit computers

The XT-IDE card will work in some 16-bit computers, but note that the primary target of the XT-IDE is 8-bit PC-class and XT-class computers.

In a 16-bit computer, the norm is to use a 16-bit hard disk controller, for performance reasons.  See bottom row of here.


Base I/O address of the IDE interface

The default base I/O address is 300 hex.  It is critical to know that if you change it, it needs to be changed in two locations:
• XT-IDE card jumpers/switches
• XTIDE Universal BIOS    (so that the BIOS knows which I/O addresses to use).


CF cards

Using a CF-to-IDE adapter, a CF card can be used in place of a 16-bit rotating-media IDE drive.  An example adapter is pictured at here.  Another is pictured at here.

Such adapters require power, so ensure that they get power.

Do not expect all CF cards to work.  There are reports of incompatibilities.

There are also reports of reliability problems in some CF-to-IDE adapters made in China (probably all made there these days).  Some do not even work from day one.  Therefore, it is prudent to purchase a few units in case one (or more) does not work properly.

A common problem with some newly purchased CF cards is that they contain non-standard boot code in their MBR (master boot record), causing a boot problem.  Discussed at here.


Disk-On-Module (DOM)

A flash based device.  A suitable DOM can be used in place of a 16-bit rotating-media IDE drive.

Required is the PATA/IDE type of DOM, with 40 pins.   (Do not mistake the 44-pin variety for 40-pin.)

DOMs require power, so ensure that they get power.

Do not expect all DOMs to work.  There are reports of incompatibilities.


Incompatibilities/Problems

Some incompatibilities exist, mainly due to the fact that XT clones are never 100% copies.

Some will be discussed in the following VCF threads:
Main thread for XT-IDE
XTIDE Universal BIOS

Some known problems/issues are shown at here.