These pages contain information about Adapter Description Files (ADFs), their structure, purpose, and how to differ between their many variants.
Content created by Peter Wendt (original HERE). Modified by Tomáš Slavotínek.
One of the most important things to know about the Micro Channel Architecture
(MCA) is the use and purpose of the Adapter Description Files - or ADFs as they
are called in short.
Unlike the "Industrial Standard Architecture" (ISA), MCA is an intelligent bus,
and it can query which cards are currently installed in the system. The ADF contains
information about the card, its name, the resources it requires and the selectable
options. The primary ADF is a plain-text file, so it can be viewed
(and very carefully edited) with any usual text editor.
This is the reason why it's so important to have the corresponding Option Disk for any new MCA card at hand, before installing it to a MCA machine. If you don't have the right ADF, you won't be able to use the adapter. The system does not know which settings and resources the card requires, therefore it stays disabled and you end up with a configuration error any time you power on the machine. This will keep happening until you either provide the correct ADF, or remove the adapter, and re-run the Configuration Utility.
Over the years Peter and others collected ADFs for most of the MCA adapter cards that were ever made. If you know what you are looking for, go to the ADF Page and look if we have what you need.
If you have ever checked the directory of your reference disk you have probably noticed that there is a lot of files with the .ADF extension. But how does one tell which one(s) is/are needed for a particular card?
First we have talk about something called "Adapter ID". This unique* identifier consists of exactly 4 hexadecimal digits, and can be read by the MCA bus from the card. This gives us hexadecimal values from 0000 to FFFF - which is 65.536 values in total for us decimal humans. The card ID was given to the card's manufacturer by IBM, and it has to be present on the card so it can be read out by the POST routines and by the Configuration Utility.
* There were some manufacturers that used the same card ID for an entire family of cards. To make things even worse, some IDs were used by 2 or more totally different adapter boards.
Some years ago Peter wrote a program called QBMCA, which can be used to identify unknown MCA cards. It can be downloaded from the QBMCA page.
Adapter Card ADF Files
ADF files beginning with @, C, and I are associated with adapter cards:
Where xxxx is Adapter ID.
Planar Board ADF Files
The other files beginning with D, P, S, or J are used for planar boards and their setup. Similar to adapters, planars also have unique IDs assigned to them.
Where xxxx is Planar ID.
Expansion Unit ADF Files
The last defined prefix - E, is reserved for MCA Expansion units that can be used to extend capabilities of MCA-based laptops/notebooks. The 3550 Expansion unit has Planar ID E9FF and it has this unique file associated with it:
* While some of the ADF files use the standard DOS executable format, they can't be used as a standalone programs, they require SC.EXE and its resources to be loaded in memory.
The text above described the relation between the adapter card and the ADF files.
Usually the card manufacturer supplies an Option Disk together with every
adapter. The option disk can contain many different files, but one file that must
be always present is the @xxxx.ADF Adapter Description File.
The basic rules when installing a new MCA adapter are:
The "Copy an option disk" program does quite a lot:
Some people install the hardware first and wait until the "Set configuration" utility complains about a missing ADF until they push in the option disk into drive A: and let the files load. While this usually works, it's not the right approach. The main reason being that the files are not copied for permanent use onto the reference disk and sometimes not all required files are loaded. This might end up in an invalid configuration or cause other trouble.
The same problem might occur, when someone manually copies the files from a ADF collection directly to the reference disk. This may work sometimes - but it will not work in all cases. I'll give some examples in the last chapter. It is a method for emergency cases or rare adapters to which option disks are no longer available, but it may not always give you the desired result.
The ideal approach is to get the right option disk and use the "Copy an option disk" option from the reference.
Most of the information presented here was taken from the following manual:
IBM Personal System /2 Hardware Interface Reference Manual - Architecture
The manual includes additional info about ADPs and Initialization programs that was missing from the earlier releases.
Further information was obtained by reading through several hundred different ADFs and studying their content...