g802

This is a 64kB dynamic RAM card. Up until the release of these, the best
that could be managed were the standard Nascom cards. This version
finally beat the dreaded “RAM plague” that had caused so many problems
in the past. It also introduced the potential to add incredible (at the time) amounts of RAM to the system.The more alert of you (sit up at the back there!) may have realised that, since the Z80 is an 8-bit
processor, 64kB is the maximum addressable memory – so where does
the EPROM fit into the space? The secret lies in this card’s ability
to be paged in and out of memory space in chunks. At the right-hand side
is a soldered header marked SK1. This is used to allocate four 16-kB RAM
areas to four outputs from an address “latch” circuit. In addition to this
the board can be selected to one of four “pages” via a slide switch in the bottom row of ICs. Thus the user can have four of these cards on a system to give a maximum of 256kB of RAM. Not too bad for a Z80!