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Commodore PC BIOS chips

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KenEG

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Oct 20, 2016
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Cincinnati, Ohio USA
This seller http://myworld.ebay.com/uniquesoftware has a supply of BIOS chips for PC10/20/30/&40 Commodore computers. I just bought a 4.41 (latest I think) chip for my Commodore Colt (PC20-III). I had just bought an EPROM burner and was actually looking for blank EPROMs when I found this. Does anyone here know what type of EPROM the Colt uses and where to purchase? I do still want to learn how to make my own BIOS chips.
 
This Page has Bios images for the PC10/20 etc and list's the Eprom types / Size, Just common Eproms by the looks of it, Available on ebah / Mouser etc.
 
Malc said:
This Page has Bios images for the PC10/20 etc and list's the Eprom types / Size, Just common Eproms by the looks of it, Available on ebah / Mouser etc.
Click to expand...

Just to add, I'd get Intel or AMD Eproms if you can, Others may work fine but if those boards are anything like IBM XT's there are some Eproms that don't work in them, I have little experience with the PC10/20 etc.
 
Just popped up: the PC20-III has an onboard 8-bits IDE controller. But the drives for it are rare so I installed XTIDE. Later I bought Sergey's Xi8088, installed an AT FDC/HDD card, connected a CF card (needs only 8 bits) and installed the XTIDE BIOS in the EEPROM meant for the BIOS. I only had to change the original BIOS to tell it to look for the XTIDE BIOS in the Fxxxxh range.
The idea: what about installing a HDD card (or a FDC/HDD card with a disabled FDC), a CF card and replacing the original 8-bits IDE routines by the ones needed for the XTIDE? Would save me a XTIDE card that I can use in my IBM-XT. IMHO the BIOS doesn;t even have to be changed.
But if interested, I started to disassemble the BIOS of the PC20-III and created one with a much faster RAM test. Just ask.
 
Ruud said:
Just popped up: the PC20-III has an onboard 8-bits IDE controller. But the drives for it are rare so I installed XTIDE. Later I bought Sergey's Xi8088, installed an AT FDC/HDD card, connected a CF card (needs only 8 bits) and installed the XTIDE BIOS in the EEPROM meant for the BIOS. I only had to change the original BIOS to tell it to look for the XTIDE BIOS in the Fxxxxh range.
The idea: what about installing a HDD card (or a FDC/HDD card with a disabled FDC), a CF card and replacing the original 8-bits IDE routines by the ones needed for the XTIDE? Would save me a XTIDE card that I can use in my IBM-XT. IMHO the BIOS doesn;t even have to be changed.
But if interested, I started to disassemble the BIOS of the PC20-III and created one with a much faster RAM test. Just ask.
Click to expand...

Thanks, but I am trying to keep the machine fairly stock. All I want is the updated Commodore BIOS so I cam use the full 42MB capacity of my hard drive. When I get more time, I want to try configuring an XT-IDE as secondary and see if I can use a DOM also. Maybe even a DOM and a CF at the same time so I can use the CF to transfer in software and back up the hard drive and DOM. If I can get that to work, I will put the CF reader in the opening that doesn't have a slot behind it.
 
KenEG said:
All I want is the updated Commodore BIOS so I cam use the full 42MB capacity of my hard drive.
Click to expand...
So far I only saw 20 MB 8-bits IDE drives and they are rare. I never saw or heard of a 42 MB one, do you have one?
 
Ruud said:
So far I only saw 20 MB 8-bits IDE drives and they are rare. I never saw or heard of a 42 MB one, do you have one?
Click to expand...

My Tandy 1000 TL/2 came with one fitted when new (Tandy 40MB SmartDrive) and I have a couple I keep as spares but none of them in my Commodore PCs, my PC10, Colt, PC20, PC40 are all on external cards, I guess it was cheaper when new.

Use of "anydrive" might be able to get around the issue of only supporting 20MB?
 
Ruud said:
So far I only saw 20 MB 8-bits IDE drives and they are rare. I never saw or heard of a 42 MB one, do you have one?
Click to expand...

Yes, I got very lucky right after I bought the Colt and found a Seagate ST351A/X on eBay at a very good price. It works perfectly in 20MB XT mode. It can be jumpered to be an AT drive, or an XT drive at 10, 20, 30, or 42MB. Since my first IBM PC compatible was a Colt with 20MB drive, I bought this purely for nostalgia.
 
I finally got time to install the BIOS chip today. Part of the delay was backing up the drive.

Installed BIOS and rebooted. Boot seems faster. Every thing good.
Changed jumper on drive for 40 MB and rebooted. Failed as expected.
Booted DOS 3.2 floppy and ran fdisk. Only allows one partition of 32 MB.
Booted DOS 5 floppy and ran fdisk. Created 21 and 19 MB partitions.
Formatted c: and transferred system files. Boots off hard drive fine.
Formatted d: and restored my data, moving all games to d:
Everything works great! Besides allowing larger hard drive and booting faster, the BIOS now detects the game port on my sound blaster.

It was a lot of work, but I am happy with the result. The backup and restore was most of the work. Changing the BIOS chip was easy once I figured out which one to change. For future adventurers, it is the one you can get to without removing the PSU and drives. Wish I had known that going in! LOL The old BIOS chip isn't labeled in a way that you can readily tell. The new one is.
 
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