ViTi95 wrote on 2021-09-16, 08:28:
Also happens that 386 and older processors suffer from very slow RAM memory transfers, the less you use it, the better.
If EMM386 is used, for sure. It utilizes both the Memory Managment Unit (MMU) and the Virtual 8086 Mode (VM86/V86), a sub mode of 80386 Protected Virtual Address Mode .
Unfortunately, using V86 in this way causes a slow-down on a 80386 processor.
The issue was fixed in late 80486 processors with the advent of VME - the one the AMD Ryzen messed up years ago.
Edit: QEMM7+ and 386MAX? supported VME, which was considered a valued feature of the new 586 (Pentium) CPU.
Edit: In pure Real Address Mode or Protected Virtual Address Mode, without V86, the performance is better.
So as a workaround, using hardware solutions for UMB and EMS make sense on 486 systems and before. At least on plain DOS.
If no dedicated hardware is available (UMB/EMS boards on bus), chipsets can provide these.
They will likely also cause little to no bottleneck, by comparison.
Edit: Utilities like UMBPCI will provide some sort of chipset UMBs, through the use of shadow memory intended for PCI bus.
Unfortunately, support on early 486 era VIP motherboards is flaky.
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