Thanks a lot! You have confirmed my suspicion, which I have now tested for.

Unfortunately, I didn't have any parity 256K modules, so I also tested with 4x 1 MB modules. I found that the RAMpAT board was more likely to read the full 16 MB when installed using 9-chip modules, rather than 3-chip. With the 3-chips, I was sometimes getting 12160K or 8192K detected.

I do not quite follow the numbers on the RAMpAT config file.

It looks like config is counting the existing motherboard memory as 4096K - BIOS SHADOW (64K) - VGA SHADOW (32K) - SCSI SHADOW (32K) = 3968K. But then why is the "next starting address" at 4352K? Should be at 4096K (I think).

Furthermore, the config utility then looks to be eliminating all of the motherboard's system memory except for 640K conventional, then adding the RAMpAT amount (16384K) minus 128K = 16896 K total memory. Complicating matters, the DOS mem command shows 15872K total memory. Is anyone able to make sense of this?

I ran Windows 3.11 IE5, loaded google, with the 16 MB on the RAMpAT. No issues there.

Ran a DOOM/Quake comparison with and without the RAMpAT

16 MB w/RAMpAT
DOOM = 21.28 fps
Quake = 2.5 fps

16 MB on motherboard only
DOOM = 21.57 fps
Quake = 3.1 fps

Rests were run on a SiS Rabbit board with an IBM BL3-100 (3x66) and ISA at 13.3 MHz. Graphics was GD5434 ISA.

Nice.
My understanding is that the total combined addressable memory RAMPath can provide is 16Mb.
It is not clear to me if that is a sum of 4Mb on-board + 12Mb from the card, or 1Mb on-bard + 15Mb.

feipoa wrote on 2023-02-06, 11:23:

It looks like config is counting the existing motherboard memory as 4096K - BIOS SHADOW (64K) - VGA SHADOW (32K) - SCSI SHADOW (32K) = 3968K. But then why is the "next starting address" at 4352K? Should be at 4096K (I think).

There is no normal RAM between 640KB and 1024KB. The 640KB conventional memory is located between 0KB and 640KB. The extended memory starts at 1024KB. If your board provides 3328KB of extended memory, that memory is located at addresses between 1024KB and 4352KB. You are correct that the simple way of dealing with on-board memory would map the 4MB of mainboard memory to 0KB to 4096KB. As the address space between 640KB and 1024KB is reserved from expansion cards, the 384KB of memory mapped to that area is inaccessible. Some of this memory is used for shadowing, but the remaining memory would be "lost" if the chipset didn't support memory relocation aka memory remapping. This remapping moves some of the memory between 640KB and 1024KB to high address past 4096KB. The amount of memory that can be relocated in different configurations (shadow for some addresses enabled/disabled) varies depending on chipset, and for certain chipsets also on total memory size. Your chipset seems to be doing the perfect job: You need 128KB of memory for shadowing, so there is up to 256KB that can be relocated, which is actually the amount that is relocated on your chipset.

feipoa wrote on 2023-02-06, 11:23:

Furthermore, the config utility then looks to be eliminating all of the motherboard's system memory except for 640K conventional, then adding the RAMpAT amount (16384K) minus 128K = 16896 K total memory. Complicating matters, the DOS mem command shows 15872K total memory. Is anyone able to make sense of this?

The highest address that can be provided by an ISA bus card is 16384KB. As extended memory starts at 1024KB, the maximum amount of onboard + RAMpAT extended memory is 15360KB. Furthermore, your board is a 386SX board with just 16384KB of total address space. The 80386 processor starts executing at the end of the address space, so the highest 64KB get allocated to a second copy of the BIOS ROM (which will always map to the hardware ROM, even if the ROM at F000:0000 is mapped to shadow RAM). This reduces the theoretical maximum amount of extended memory by another 64KB to 15296KB. The MEM output shows another 64KB less, so I guess your chipset reserves the top 128KB for ROM access.

pshipkov wrote on 2023-02-06, 16:19:

Nice.
My understanding is that the total combined addressable memory RAMPath can provide is 16Mb.
It is not clear to me if that is a sum of 4Mb on-board + 12Mb from the card, or 1Mb on-bard + 15Mb.

The memory on board can not be disabled by the RAMPpAT card. To avoid conflicts, the RAMpAT must not respond to cycles that are also handled by the 4MB onboard RAM. So you will most likely get 4MB on-board and just short of 12MB from the card.

Agreed.
Never put much thought into how memory expansion cards work.
All your comments make sense.
Thanks for that.

Thank you for the perfect explanation (again!). The particular board that I was testing on is a Chaintech 340SCD based on the SiS 310/320/330, aka "SiS Rabbit". It is a 386DX motherboard that supports 32 MB DRAM. There is not an option in the BIOS to allow for memory relocation, but from what you've written, it sounds like it is relocating memory by default. When using BL3 chips on 386 boards, I usually avoid memory relocation because of higher chances of memory errors. With 16-32 MB of RAM installed, another 64K-256K doesn't matter much. No such issues with the remapping on the SiS Rabbit.

I did install the RAMpAT into my 286 and found that my RAMpAT config screenshot matches that of pshipkov's, implying that the system is not relocating unused reserved RAM. Unfortunately, when using the RAMpAT in my 286, I would get

1PARITY ERROR ???
2SYSTEM HALTED_

when trying to run DOOM. I tried different modules to no effect. I was able to load Win3.11 fine. I also was able to finish the Quake timedemo. It look around 25 minutes and the score was incredibly low at 0.7 fps. A 286 with 16 MB RAM at 66 MHz w/1K L1 doesn't feel anything like a 486.

I ultimately put my enormous 3 MB Everex EV-159 back into the 286 because it didn't have parity RAM errors with DOOM.

feipoa wrote on 2023-02-07, 04:13:

I did install the RAMpAT into my 286 and found that my RAMpAT config screenshot matches that of pshipkov's, implying that the system is not relocating unused reserved RAM. Unfortunately, when using the RAMpAT in my 286, I would get PARITY ERROR ??? SYSTEM HALTED_ when trying to run DOOM.

Doom requires a 386 because of its built in memory manager, no?

I'm using a 286-to-486 upgrade: Cx486SLC2-50MP at 66 MHz.

All, I am having a little different issue. I am not sure if is because my system board only has the 512Kb or if there is some other issue. The card installs correctly. I am running an IBM5170 with the QUADTEL BIOS upgrade. The Config sees the memory. The Install.exe also sees the memory. See attached pics. When it reboots, the BIOS counts through the memory and then gives an error: 3082 Memory Fault error. FAULT is at FFFFFFFF. As long as I do not have EXPANDED memory configure, the system will continue to boot up to the DOS command prompt.
When I run "mem" from the command line, it does show all the memory. However, except for the conventional memory, there is "0" free memory. Nothing is available.
A few notes:
* The battery is dead. I have to reconfig BIOS if the PC is off for more that 2 minutes.
* I do not have 128Kb memory expansion card. The system is running with only the 512Kb on the motherboard, plus the RAMpAT card.
* I am unsure if the motherboard is Type 1, 2 or 3. MSD does not recognize the processor (unknown).
It is not type 3 based on the BIOS layout on the motherboard.
It is running the original MFM controller card. However the QUADTEL BIOS does allow me to operate a 1.44 mb 3.5 disk drive.