Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cwjcc!hal!ncoast!dchou From: dchou@NCoast.ORG (David Chou) Newsgroups: comp.sys.ibm.pc Subject: IBM-AT BIOS ROMS Message-ID: <1989Sep24.073912.16557@NCoast.ORG> Date: 24 Sep 89 07:39:12 GMT Organization: North Coast Computer Resources Lines: 24 I would like to thank more than a dozen respondees regarding the updating of the original IBM-AT BIOS ROMS. Most of the respondees pointed that the last location of the romset contained the byte which serves as the checksum value (location FFFFF). The next to the last byte contains the PC ID byte (FC for the AT). It is a rather simple matter to reprogram locations in the various ROMs and then adjust the last byte. Several pointed out the the ROMs are paired odd/even bytes. Several also mentioned that there are BIOS sold by third parties which work in the AT. However, I specifically called Phoenix who cautioned me against buying a BIOS not tailored for my machine. Well anyway, I took the easy way out. I located several IBM-ATs and using the program posted to the net, found a machine with the appro- priate disk type which I needed (1024 cylinders, 7 heads, 26 sectors - I know this is not quite right for the 3085 which has 1170, but it is close). The first machine had ROMs which for one reason or another I could not copy. The second machine had EPROMs (27256's) which copied nicely. Incidentally, these old motherboards have a jumper dip at location U131 which when reversed supports either 27128 or 27256 EPROMS. I am still having trouble with my Miniscribe 3085 but that is another story not related to this subject. David Chou ncoast!dchou@hal.cwru.edu dchou@ncoast.org