SPAM-1's RAM is 64k by 8 bits.
It is connected to the ALU output bus and the ALU B-Input bus.
The RAM is written to by data flowing from the ALU result bus. The RAM is connected to the ALU result bus via a tristate buffer (see 'BUFFER IN' above) to avoid interference between the ALU result bus and the ALU B input bus as the RAM's data lines are connected to both the busses. When the RAM is read it places a value on the ALU B input bus via a tristate buffer.
The RAM may be addressed in one of two ways:
- Register addressing via the memory address registers or
- Direct addressing via an address supplied by the program ROM
Because the RAM emits data only onto the ALU B input B then RAM values may only appear on the right hand side of ALU operations eg REGA = REGB + RAM[$1234]