ryandesign
commented
4 months ago I've observed this slowness too, definitely on 800K HFS disks but I'm not sure that 400K MFS disks are completely unaffected. I assume it's not an intentional slowing down but rather a continuation of the disk reading issues I've reported with the Apple II Disk II emulation since Macintosh disks are similar and share code in Clock Signal. I hoped that continuing to tackle those Apple II disk issues would improve the reliability of Macintosh disk access too. I assume the Macintosh is just having trouble finding the sectors it needs and is having to retry many times before finding them, thus slowing things down. By adding head position logging I see when booting to an 800K HFS disk that the head keeps making wild swings all across the disk, repeatedly returning to track 0 after almost every read, as if needing to reset back to a known position after getting lost.
800k disks don't seem to be emulated properly on Macintosh. It takes an unrealistically long time to boot from a System 6 disk and the emulated machine is so unresponsive that it's unusable. I did a test where I booted from a hard disk image and copied the same 400kb file to a blank 400k and 800k disk and these were my results:
400k disk Write - 45 sec Read - 18 sec
800k disk Write - 235 sec Read - 145 sec
I think the emulator is slowing down the speed of the drive too much because the read and write speeds should be more or less the same between these two.