wondow wrote on 2025-12-09, 15:42:

If I understand correctly your message, even on a slow 386sx (16 or 25), Emm386 would be faster? It was my understanding that for slow CPU, EMS is the preferable way, as it is much faster than XMS. The only advantage would be to stay on Real mode for maximum compatibility?

I was trying to say that if you are using an 8 Mhz computer, running your programs from memory on an ISA card instead of memory directly attached to your motherboard chipset has a performance hit, but it is relatively small. Mainboard memory will probably have 0-2 wait states while ISA memory cards will usually have 3-5 wait stats. There is overhead going out to an ISA card. A rough comparison is that your 8 Mhz computer will perform like a 6Mhz computer when running from ISA memory. Not ideal, but not fatal.

But if you are using a 16Mhz computer, the performance hit is more noticeable. Mainboard memory access is probably still < 3 wait states, but ISA memory access is now 8-10 CPU waits. A rough comparison is that your 16 Mhz computer will feel like an 8 Mhz computer if you are running programs from an ISA memory card. You will feel it. So maybe ISA memory is better than nothing if your workload really needs the ram, but you certainly wouldn't want to use ISA memory if you could in anyway get the same functionality from mainboard memory. And the problem just gets worse with faster systems that have memory caches, because ISA memory is not uncacheable.

Now if you have to stay in real mode, then an EMS card might be the only option if you don't have a system board with a chipset that supports EMS from mainboard memory.