Hunting for the rare 5700051 IBM 5150 bios

Does anyone here have an IBM 5150 with the original 64k-max motherboard, and the first version (chip labeled 5700051, date 04/24/81) bios rom at location U33 on the mainboard? I've been trying for over a year to track one down, and have had no luck. All the people who owned such machines that I knew of had already sold them.

If you have one of these motherboards, please follow the instructions here: http://mess.toseciso.org/dumping:dump_bios_using_debug
And private message me so we can arrange transfer of the resulting MYF000.bin and MYF800.bin files.
This is for preservation purposes, as this rom is very nearly completely lost at this point!

...Now I know someone will say "If I dump that ROM from my system which I paid so much for, people will just copy it and stick it into less valuable 5150 systems to make quick cash".
Well, that's indeed possible, BUT: there's a relatively easy way I know of to tell if a MB has been 'upgraded' with a 'fake' non-ibm-made rom. It does require access to the machine, but it should be able to tell even a re-silkscreened windowless otp eprom apart from a real original IBM part, even if the contents are the same. It has to do with the distinct electrical characteristics of the ROMS IBM used, which are *very* different from any conventional EPROM or windowless OTPROM. The IBM roms are of a very specific and consistent type, and anyone with an eprom reader/programmer can relatively easily check whether the rom is legit, assuming they have a 2364-to-2764-pinout adapter. <instructions to come later, I need to run >

LN

See this: http://members.dodo.com.au/~slappanel555/bios.htm site.

Wait, so are you telling us that you can make a few extra bucks out of selling your old 5150 by having specific BIOSes in them? I never heard of that before and never really knew it was an issue.

WHOA! that rom was NOT on that site when I checked last in november.
I checked it quickly against the 2nd rev bios and indeed it seems to be correct!
My thanks to whoever uploaded it!

Now, as promised, how to tell apart real ibm chips from fakes:
The IBM roms as used on all of the 5150 mainboards, (and on many but not all of the 5160 boards, however the roms on these boards are 23256 and not 2364, but the same idea applies) are NOT real 2364 mask roms, they're called MK36C35, and they require an odd thing:
They must get a low-high-low pulse on /CE to latch the address lines before the chip will update the address.
Most eproms are asynchronous and don't need this.
Hence, if you dump real IBM roms by pulling /CE low, you'll get a dump with all of the bytes of the dumped rom exactly the same as the first byte (i.e. if the first byte is 0x0a, the whole rom will be nothing but 0x0a repeating), as the address inside the rom is never updated.
On non-original roms (MCM68764 or MCM68766 are one of the rare eprom 2364 equivalents), the rom will dump correctly.

Remember a 2364 does NOT have the same pinout as a 2764; a 2364 is 24 pins while a 2764 is 28. See http://mess.toseciso.org/dumping:2364_mask_roms

Thanks again!

LN

Lord Nightmare said:

WHOA! that rom was NOT on that site when I checked last in november.
I checked it quickly against the 2nd rev bios and indeed it seems to be correct!
My thanks to whoever uploaded it

Click to expand...

The dump was kindly supplied by 'the xt guy'.
See http://www.vintage-computer.com/vcforum/showpost.php?p=75157&postcount=44

I owe him a beer

LN