[danmg]

PCem shines for emulating all the old hardware required to run old operating systems that were not DOS. VirtualBox and VMWare do not work will for this since they usually since they don't have guest extensions and working drivers for things like OS/2 2.1 and Slackware 3.0.

[anthk]

Qemu can emulate an ISA pc, with a Sound Blaster and a Cirrus ISA VGA just fine.

People has been running really old Slackware releases under Bochs/Qemu since forever.