Emulation of hard drive/floppy drive speed for late 1990s PCs

[frank-deng]

It seems that the hard drive I/O speed of DOSBox-X is far too fast compared with 1990s PCs, almost as fast as late 1990s RAM when running DOSBox-X on PCs equipped with modern SSD. I'm not sure whether such behavior will cause problems when running some demoscenes/games, and is it appropriate to use a configuration for slowing down hard drive I/O speed when encountering such problems? When running Windows 95 inside DOSBox-X on my new PC equipped with SSD, I found that the desktop finished loading almost within 1 second once mouse cursor appeared on the screen. On real machines from late 1990s, it should be almost 1 minute to finish loading desktop.

[joncampbell123]

So far, slowdown is only applied to INT 21h disk I/O emulation. You are absolutely right in that INT 13h emulation needs to do the same.

I know of one demoscene executable (380 volt) that will hang at one transition point IF file I/O is too fast.

[frank-deng]

I also tried to use nbd+trickle for emulating a slow hard drive access under Linux, it seems that such method just hangs the whole emulator before the I/O operation finished.

[frank-deng]

Also, is it possible to apply slow-down feature at raw I/O level in case the guest OS handles hdd I/O directly without using any BIOS interrupts?

[joncampbell123]

@frank-deng So, add the I/O delay to INT 13h, and then also adjust the IDE emulation to delay between receiving a command to read/write and completing it by the same I/O delay?

[frank-deng]

Maybe it's easier to implement INT 13h 's delay first, then implement delay at IDE emulation level later.

By the way, is it possible to implement delay for floppy & cdrom also altogether?