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IBM 5170  -  BIOS Revisions


The BIOS (including BASIC) is 64 KB in size.

On very early 5170 motherboards, there are four 16 KB sized BIOS ROM chips (of type 27128), in sockets U17/U27/U37/U47.  Later, two 32 KB sized BIOS ROM chips (of type 27256) were supplied instead, one in socket U27 and the other in socket U47.  5170 motherboards of type 1 have a shunt block designated U131, which is set according to the type of ROM's fitted.

These are 8-bit chips which, in matching pairs, supply 16 bits to the IBM 5170's 16-bit data bus.  U17 and U37 are one matching pair, and U27 and U47 are the other matching pair.  A diagram showing how pair U27/U47 supply 16 bits, is at here.

There were 3 revisions of the BIOS, differentiated by date (there are no version numbers).
The table below lists the dates, and the unique 7-digit IBM part numbers that are located on the top of the ROM chips.

The date format used is MM/DD/YY.

	Part numbers, where BIOS supplied in masked ROM form	Part numbers, where BIOS supplied in EPROM form	Supplied on motherboard type	Floppy/diskette drive support	Hard drive support
01/10/84	U27=6181028, U47=6181029   (photo)	U17=6181024, U27=6181025 U37=6181026, U47=6181027   (photo)	Type 1	Click here	Click here
06/10/85	U27=6480090, U47=6480091   (photo)	U27=6448896, U47=6448897   (photo)	Type 2	Click here	Click here
11/15/85	U27=62X0820, U47=62X0821   (photo)	U27=61X9266, U47=61X9265   (photo)	Type 3	Click here	Click here

Some additional BIOS ROM part numbers are shown in figure 9 of the document at here.

Click here for content images (can be used to create replacements).


BIOS upgrades

Supported by IBM was an upgrade from the 01/10/84 revision to the 06/10/85 revision.  How do we know that? To owners of 5170s that had the type 1 motherboard, IBM made available a 30 MB hard drive upgrade kit, and that kit included 06/10/85 ROM's (required to support the 30 MB drive, of type 20).

It is unknown if IBM supported/endorsed an upgrade to the 11/15/85 revision.  This upgrade is desirable to some 5170 owners, because it provides BIOS support for 1.44M diskette drives (e.g. ability to boot from a 1.44M diskette in A:).  There is a small amount of concern here because a BIOS designed for an 8 MHz clocked motherboard is going into a 6 MHz clocked motherboard.  I have not heard of any problems from people who have tried this upgrade.  I tried it myself for a while, and I did not encounter any problem.

Besides an upgrade to the IBM BIOS' shown above, you also have the option of upgrading to various third party BIOS' (e.g. AMI, Award, Pheonix, etc.)  Some of those BIOS' are available here.

Unlike with modern computers, you can not simply 'flash' a new BIOS onto the 5170 motherboard - you need to physically replace the two BIOS ROM chips.  New BIOS ROM chips are normally created by 'burning' an image of the BIOS into suitable EPROM chips (via an EPROM programmer).  See the 'IBM 5170' section of here.  Click here to see some people/companies that can supply and 'burn' EPROM's for you.


Known problem - POST error of 601

With the second (06/10/85) and third (11/15/85) BIOS revisions, removing the IBM Fixed Disk and Diskette Drive Adapter and substituting a third-party replacement solution can (can, not always) result in a 601 error during POST (Power-On Self Test).  There is something in those revisions that expects the 'IBM Fixed Disk and Diskette Drive Adapter' (or compatible card).  The symptom is not seen with the first BIOS revision (01/10/84).

In this situation, the 601 error is the POST warning you that it not find the 'IBM Fixed Disk and Diskette Drive Adapter'.

Note that if experienced, this does not stop the boot process; following the 601 is a prompt to press the F1 key to resume, although, floppy operation may be compromised.

One fix is to use a replacement solution that behaves the same as the 'IBM Fixed Disk and Diskette Drive Adapter', i.e. the POST will believe that an 'IBM Fixed Disk and Diskette Drive Adapter' is fitted.  An example is the Western Digital WD1003A-WA2  (I know because I have tried it with the two '85 dated BIOS).  The WD1002-WA2 and WD1003-WA2 may also be suitable.

Another fix could be to use the 'patched' IBM 5170 BIOS that is discussed at here.

Substituting the IBM BIOS with a third-party one, is a known workaround.


A  HYPOTHESIS

Could it be that in the year (roughly) after the IBM 5170 was released, some owners, ignorant of the fact that the floppy controller functionality in the IBM 5170 needs to support three data rates (250/300/500 kps), were for whatever reason, substituting the supplied controller (informally known as the 'combo' controller) with a double density floppy controller (i.e. 250 kps only). Such owners would not see a 601 error at computer start-up time, and then be puzzled as to why the 1.2M floppy drive did not read floppies.
As a result of that, could it then be that when the second motherboard BIOS was being created, IBM decided to add some code that produced a 601 error if the code coud not find a unique indicator that the 'combo' controller was present? At least then, the 601 error would indicate a problem.