If it's a clone, the above doesn't apply. Pull the case, and find the CPU
chip (probably on the motherboard). If it's an 8088 or an 8086, it's an
XT clone. If it's an 80286, it's an AT clone.
Unless its a 286 XT ;) In which case it probably has a ribbon cable running
from the cpu socket, connected to a Microsoft Mach 20
board in one of
the expansion slots.
-Lawrence LeMay