The MR BIOS adds LBA28, support for configuring up to 8 IDE drives, 4 floppies, 4 parallel and 4 serial ports. For the early to mid 90s that was a huge improvement for most 486 machines that were often stuck at CHS 504MB drive limits, might not support IDE optical drives, and sometimes only supported 2 IDE and 2 floppy drives. OK the 2 floppy drive limit was not a problem.

It arrived, a day earlier than expected. Now I can actually read and write chips. I have no idea what 90% of these adapters are for, but it seems to have just about everything covered.

lsorense wrote on 2026-02-10, 15:13:

Or perhaps the flat blue line means write back caching is in fact not working?

As noted by gigahertz the blue line is always flat on a 486 regardless of WB/WT

lsorense wrote on 2026-02-11, 16:02:

It arrived, a day earlier than expected. Now I can actually read and write chips. I have no idea what 90% of these adapters are for, but it seems to have just about everything covered.

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nice!
these programmers are very easy to use , we already know the BIOS is a 64kbyte one so it is a 27C512 type chip
there is no need to remove the sticker to find the exact maker/model of the chip - they are all standard devices and the programmer will read the same data
so first select the AM27C512 DIP28 chip from the list (press on the big button that has the chip model) , uncheck the "Check ID" option and finally press the READ button
do a couple reads and see if the checksum remains the same, if it does then just press the SAVE button and you are done! 😀

keropi wrote on 2026-02-11, 17:18:

nice! these programmers are very easy to use , we already know the BIOS is a 64kbyte one so it is a 27C512 type chip there is n […]
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nice!
these programmers are very easy to use , we already know the BIOS is a 64kbyte one so it is a 27C512 type chip
there is no need to remove the sticker to find the exact maker/model of the chip - they are all standard devices and the programmer will read the same data
so first select the AM27C512 DIP28 chip from the list (press on the big button that has the chip model) , uncheck the "Check ID" option and finally press the READ button
do a couple reads and see if the checksum remains the same, if it does then just press the SAVE button and you are done! 😀

I started by taking the BIOS out of the currently not working Pentium Pro system. Set it to 29C010 and read it and that looks correct. Now that I did that right I will attempt the SIS BIOS too although I am expecting to get exactly the same result as I got with my small program before.

Does the MR BIOS have the Y2K bug? Because that is a huge bugbear I have with the current BIOS on my Chicony CH871..

appiah4 wrote on Yesterday, 07:37:

Does the MR BIOS have the Y2K bug? Because that is a huge bugbear I have with the current BIOS on my Chicony CH871..

Which one in particular? Certainly speedsys says it has a y2k bug. It has no problem setting the clock to dates after 2000 and keeping time correctly. So whatever y2k bug it may have it doesn't seem to be causing any problems for me. From what I have read, the bug was handling the transition from 1999 to 2000, but since we are past that transition I don't think that bug matters anymore as long as the system can keep dates after 2000 which it seems to do just fine.

Certainly this is Y2K compliant enough for my uses.

lsorense wrote on 2026-02-09, 20:06:

Hmm, for some reason I didn't think that was allowed, but it does appear many people have done so. […]
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weedeewee wrote on 2026-02-09, 19:59:

Can't you just attach the file to a comment you're making here? Just like in all the other bios threads were the bios files are attached to the comments people post.

another option would be to go to theretroweb discord and do an improve board request to add the biosfile to the specific board page.

Hmm, for some reason I didn't think that was allowed, but it does appear many people have done so.

Well here it is. Maybe someone can give it a try.

The attachment MRBIOS-SIS471-V3-21.zip is no longer available

Thank you so much for posting this, you are an absolute legend! I'm just starting to mess around with this but it seems to be working. I now don't need XTIDE to access my 64GB C drive and because of that I am once again setting new PB high scores in my favorite DOS game, MEM. So far the memory throughput I've seen is a little less than what I was able to achieve with the 0402.001 BIOS, I wonder if the slight difference I'm seeing is due to the cache config as I did the piggyback tag mod. Still lots more to fiddle with.