The unexpanded ZX81 is equipped with 1K of RAM – this is either provided by 2 x 2114 chips, or a single 4118 chip. There are positions on the motherboard for both configurations.
2114 RAM Chip
- A0-A9: Address Lines
- IO1-IO4: Data Lines
- S: Chip Select
- W: Write Enable
Notes:
The 2114 chips are 4096 bit static RAM organised as 1K x 4bits, which is why two are required to make up 1K x 8bits