UNLIKE virtualbox/VM workstation PCEM strives for cycle accurate emulation of period bios hardware up to the mid 90s. Penitum II/Celeron if your host can handle it.
My current host an I7 8th gen that has a clock speed of 2.8GHZ can handle up to Pentium II 200 if it's not a Macromedia/Quicktime game or I have to make another virtual OS at a mid range Socekt 7 Penitum I series.
So again I ask why can't Microsoft make a professional job and find a way to make use of multiple CPU's as the new author of PCEM refuses to do so due to the insane amount of work it will take to utilize that aspect so thus PCEM will remain single core only which is a shame. It really limits it's potential as a 32 bit emulator due to the steep host hardware requirements.
Now if only we had a major corporation that had the money and manpower to do something like this built into several layers if necessary. Geez I wonder who that could be?