I built the additional circuitry on a 3 by 4 inch piece of Vero card
which was mounted about 2 cm. above the main board; it was held at one end by
wire-wrap pins which plugged into the empty EPROM sockets and was supported at
the other end by two insulating pillars. These were held in place by fine
insulated wire threaded through convenient holes in the boards. Connections to
the various signal lines were then made by soldering to the IC socket pins on
the underside of the main board. This made a reasonably neat arrangement of
what is essentially a bodge job.
256k RAM chips are now becoming avaiable, but unfortunately they
currently cost about £50 each, so even a single block would cost £400, which
is beyond the reach of most of us. However, the price projection is that they
will be under £10 by mid-1985. These chips require a full 8-bit refresh cycle
and a little thought is required to toggle the A7 line at the appropriate
times during refresh; a number of ingenious solutions have been suggested in
various electronic journals. I wonder who will be the first to upgrade his
board to half a megabyte?!
 INMC 80 News Vol 3, Feb-Apr 1981, page 16-17 see also
80-BUS News Jan-Mar 1982, page 12.
 80-BUS News Vol. 1
Issue 3, July-Oct. 1982, page 21-23.
 D. Allen New Electronics Vol. 17 No. 5, 6th. March 1984, page 26.