VOGONS

Weird HIMEM.SYS problem

Topic actions

First post, by anonyfous

Posted on 
User metadata
Rank Newbie
Rank
Newbie

Hi,

today I moved my 486DX4 100Mhz build to retro pc night event, everything worked fine at home, everything loaded, sound was working, all good, but when i powered the pc on at the venue I got a the "Unable to control A20 line. XMS driver not installed" error. I have tried to cear the CMOS, different RAM stick.. no luck. Finally I got it to boot by putting the /M:11 switch to CONFIG.SYS, but then the uupper memory area was unavailable. That seems odd to me, beause it worked just fine without the /M:11 switch before. What can be the possible cause? After trying to remember what was different, I realized that I used different keyboard there, could it be something keyboard related? Any help would be great, any idea?

Thanks,

Lu.

Reply 1 of 3, by jakethompson1

Posted on 
User metadata
Rank Oldbie
Rank
Oldbie

I encountered an issue like this when the CPU was one that supports write back internal cache (&EW Intel DX4 or "Enhanced" AMD DX4 in your case), and the board was properly jumpered for that, but the BIOS failed to recognize the CPUID as a write-back one and failed to configure the chipset to expect such write-back cycles. Needless to say simple DOS operations worked at first, but turned into chaos as things got more complex.

It was a PhoenixBIOS, an Am5x86, and a UMC UM498 chipset in my case.

Reply 2 of 3, by anonyfous

Posted on 
User metadata
Rank Newbie
Rank
Newbie

I have AMD Am486 DX4-100, AMIBIOS and a Shuttle HOT-419 MB with OPTi 82C895 chipset...

Reply 3 of 3, by Disruptor

Posted on 
User metadata
Rank Oldbie
Rank
Oldbie
anonyfous wrote on 2025-05-08, 21:28:

I have AMD Am486 DX4-100, AMIBIOS and a Shuttle HOT-419 MB with OPTi 82C895 chipset...

Which AMD Am486 DX4?
A SV8B or a (N)V8T?

Go to top of page Go to top of page
Back to Software
Close window
Close window