The Z88 used has two physical locations for storage.
Internal with chips and expansion cards.
...
Internally
with the 'built-in' standard 128K ROM and 32K RAM chip. Expansion may be made by changing these.
Expansion cards are easier to change using the three slots. RAM, ROM, Flash and EPROM can be used.
Externally
using the Serial Port. Other computers, Disk Drives, and cassette tape may be used.