Hi Anil,
Welcome to the list. What's a Z-90? I have a Z-100 but I've never heard
of a Z-90.
Z90, z89, z88 are version of the same system based on the H19 terminal and
a Z80 board to run HDOS or CPM. The differences were IO and disk systems.
The Z100 was 8088/z80(or was it 8085) and had a S100 bus section, very
different machine.
Allison