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.

The attachment 20260211_104920-small.jpg is no longer available

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 2026-02-12, 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.

lsorense wrote on 2026-02-11, 20:14:

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.

Of course while looking for a system with some rom chip I could try reading to test with, I went through various mini towers in the basement, open one at random looking if it has any rom chip I can borrow to look at, and first one doesn't appear to have anything, but then I notice: This boring little white tower has a 68 pin UW scsi connector on the mainboard... and some 64 bit PCI slots... Oh, it's one of the Alphas I have around. I forgot how dull the cases were on some of those. At least the blue and purple boxes are obvious for the SGIs. Alphas were very plain.

I have a Acer VI15G

The Sys 471 BIOS works, but:

• The cache is identified as 32KB by the BIOS instead of 512KB
• The main memory speed it turrible

I was using the default settings. Any idea what I might be able to tweak?

ps. It's a 486-100. The BIOS gets that correct. Speedsys doesn't.

douglar wrote on Today, 00:27:

I was using the default settings. Any idea what I might be able to tweak?

You need to short pins 16-17 on the front panel header. It seems this MR BIOS defaults turbo speed to low.

douglar wrote on Today, 00:27:

I have a Acer VI15G […]
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I have a Acer VI15G

The Sys 471 BIOS works, but:

• The cache is identified as 32KB by the BIOS instead of 512KB
• The main memory speed it turrible

The attachment SIS471_result.png is no longer available

I was using the default settings. Any idea what I might be able to tweak?

ps. It's a 486-100. The BIOS gets that correct. Speedsys doesn't.

That looks like L2 cache disabled, not that the size is wrong. It appears you are only using the L1 cache in that test. The suggestion that it is running in slow mode seems likely.

Your image all i see is that it says 32MB ram (not 32KB cache) and the graph seems to be either 8K or 16K L1 cache before dropping off drastically.

In fact the chart does say L1 is 8KB and L2 is 512KB so it seems it is detecting it, just not using it.

You can toggle between slow and fast using control-alt-numberpad plus and minus, and you can toggle cache on and off with control-alt-shift-numberpad plus/minus on the fly.

lsorense wrote on Today, 03:04:

In fact the chart does say L1 is 8KB and L2 is 512KB so it seems it is detecting it, just not using it.

It’s using the l2 cache. It’s just that the speed of the l2 and main memory is so low it gets lost in the text for “1024”

Gentlemen, it is with great sadness to inform you that this BIOS does not POST on my Chicony CH-471A Rev 3.0 motherboard.

lsorense wrote on 2026-02-09, 21:15:

weedeewee wrote on 2026-02-09, 20:47:

Ok.
Submitted.

So looking at the board, it is visually identical to a sv2gx4 rev 2.0, but does not have some jumpers and voltage regulator parts installed, and the X4 in the name is covered with a square of white paint. So it seems they were making changes to support the DX4 but kept using the same board for the older model by just leaving out the parts that it didn't need. The gx4 bios list even has mentions of a rev 1.7 board, so they went through quite a few revisions it seems.

The attachment 20260209_160838-resized.jpg is no longer available

Bios added to board:
https://theretroweb.com/motherboards/s/asus-v … 86sv2g-rev.-1.0
Board added:
https://theretroweb.com/motherboards/s/asus-v … 486sv2g-rev-1-5

evasive wrote on Today, 18:27:

Bios added to board: https://theretroweb.com/motherboards/s/asus-v … 86sv2g-rev.-1.0 Board added: https://theretroweb.com/mother […]
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Bios added to board:
https://theretroweb.com/motherboards/s/asus-v … 86sv2g-rev.-1.0
Board added:
https://theretroweb.com/motherboards/s/asus-v … 486sv2g-rev-1-5

Thanks !