Random access memory (RAM) module
The random access memory (RAM) stores the program the computer is executing as well as any data the program needs. Our breadboard computer uses 4-bit addresses which means it will only have 16 bytes of RAM, limiting the size and complexity of programs it can run. This is by far its biggest limitation.
Schematic: Memory address register (MAR)

Schematic: RAM module

Data sheets
- 74LS00 Quad NAND gate
- 74LS04 Hex inverter
- 74LS157 Quad 2-to-1 selectors/multiplexer
- 74LS173 4-bit D register
- 74189 64-bit RAM
- 74LS245 8-bit bus transceiver