I have an IBM PS/1 386SX with 4Mb of RAM soldered on board with 2 free 72pin slots. I installed 2 simm (see in the photo) the bios sees me 16Mb but memtest only 4... why???
AlessandroB wrote on 2023-02-14, 20:37:I have an IBM PS/1 386SX with 4Mb of RAM soldered on board with 2 free 72pin slots. I installed 2 simm (see in the photo) the bios sees me 16Mb but memtest only 4... why???
And how much RAM do you have really?
DOS shows 12MB, right?
So both memtest and bios are wrong? 😁
Which one is original?
The left one is not compatible with your machine. This was same issue with mine, I have a bundle of these that does not work.
Real reason is no quad CAS for left one. It is one 32 bits plus parity with one CAS is for late MCA PS/2 machines such as 8595, 9595, 77 etc. The right side is configured for 4 cas as PC standard.
Cheers,
Great Northern aka Canada.
pentiumspeed wrote on 2023-02-14, 23:14:Which one is original? […]
Which one is original?
The left one is not compatible with your machine. This was same issue with mine, I have a bundle of these that does not work.
Real reason is no quad CAS for left one. It is one 32 bits plus parity with one CAS is for late MCA PS/2 machines such as 8595, 9595, 77 etc. The right side is configured for 4 cas as PC standard.
Cheers,
neither of them is original, this model has 4Mb soldered on the mainboard and 2 free slots. I have several ibm branded simms and would have liked to use them on this computer. I have all 4mb cards except one that is 8mb and I would have liked to use it. How do I recognize the compatible ones?
Update: with this two simm seems to work… but i do not know why…
Can you configure something at memory?
Perhaps you have configured to use 4 MB as EMS.
Disruptor wrote on 2023-02-15, 15:03:Can you configure something at memory?
Perhaps you have configured to use 4 MB as EMS.
hard disk with comfiguration come from the first owner. mist i check the comfig/autoexec??
No, in the BIOS screen.
Disruptor wrote on 2023-02-15, 18:09:No, in the BIOS screen.
Nothing can be selected in the bios, only the boot order and floppy drive enable. I don't understand what you mean though, how can memory be divided into 4 megs? I'm not very knowledgeable about types of memory
Probably some of the hardware resources/bus used are shared by the onboard ram and some part of/one of the ram slots. Can you disable the onboard ram? Have you tried to put only the 8mb simm alone and test it in each slot with the onboard ram?
AlessandroB wrote on 2023-02-15, 21:18:Nothing can be selected in the bios, only the boot order and floppy drive enable. I don't understand what you mean though, how can memory be divided into 4 megs? I'm not very knowledgeable about types of memory
On my 386SX I can decide how the upper memory is split into extended or expanded memory.
For example, I can define to have 11 MB of extended memory and 4 MB as expanded memory. But I also can allocate 15 MB as extended memory.
In my 386SX I have 20 MB of RAM although I know that the 386SX cannot address more than 16 MB. But my chipset allows me to use that 4 MB as expanded memory. However, I also could split my 20 MB into 8,5 MB extended memory and 10,5 MB expanded memory. I just have to define that in the BIOS.
Note that lower 1 MB is reserved for conventional memory + shadow RAM.
Top three 4MB modules is correct for your PC, and no parity and that PS/1 is actually standard low end "generic" PC.
Bottom four modules are for late PS/2 only, sell them to for late PS/2 owners.
I'm intending to sell mine when I get a chance.
Cheers,
Great Northern aka Canada.
pentiumspeed wrote on 2023-02-16, 00:04:Top three 4MB modules is correct for your PC, and no parity and that PS/1 is actually standard low end "generic" PC. […]
Top three 4MB modules is correct for your PC, and no parity and that PS/1 is actually standard low end "generic" PC.
Bottom four modules are for late PS/2 only, sell them to for late PS/2 owners.
I'm intending to sell mine when I get a chance.
Cheers,
I think I'll keep the modules for the PS/2, sooner or later I want to get a 286 MCA PS/2 to have it in my collection. You tell me that the computer works with 4 modules that have 8 chips, but as you can see from the photos I posted above, it "seems" to work instead with two modules that have 9 chips. I'm a bit confused...
I'm talking about the 9 chip per side modules on that proprietary modules. All chips on these are same part number, meant one CAS line and 3 bits per chip. These are for *LATE* PS/2 that uses 486 and Pentium. I turned up a documentation on what this modules are used in certain models. PS/2 286 and 386 does not support this, they use 1MB or 2MB modules 85ns and 80ns only because I used to have collection of PS/2 in back then and had decent knowledge of these.
Late PS/2 I refer to models like 8595, 77, 9595 etc which are all made after 1990, meant are late models, Sell these and buy correct modules for PS/2 286 or PS/2 386.
The standard PC 72 pin simms are always 4 cas modules meant they build the memory circuit in 4 bank format divided in four sections of 8 bits at a time plus 1 bit parity (optional) hence 4 cas meant requires if simm has parity will have four 1 bit parity memory ICs or one 4 cas 4 bit parity IC which is shrunk to one IC from four 1 bit parity ICs with 1 cas each. This four CAS for standard (read clones) design was to be compatible with 286 and 386SX using 72 pin simms allowed this to use split into two 16 bit apiece per 72pin simm.
In fact that happened to be true on Compaq 386 series 32 bit proprietary memory expansion board still have four CAS modules but for soldered 1bit chips on the expansion board is also 32 bits, compaq simply split the 32 bits plus 4 bits parity into two sections as I mapped out the layout on paper and multimeter readings meant I cannot use a 72 pin simm wired in. I must use 30 pin simms two of them wired together at a time.
Cheers,
Great Northern aka Canada.
