Zx81 Memory Map, Here is the memory map of the ZX81 (assuming the ZX81 has 16K of memory). To resume, the calculator stack is an area of memory that the ZX81 uses to store any temporary results generated while it is doing arithmetic. RAM Memory Expansion While resourceful owners could accomplish a lot with the 1K or 2K of RAM built in to their computers, more serious uses required more RAM. Other very popular computers were the Commodore 64 and the Apple II but were far more expensive (ZX81 was ten times cheaper than Apple II Plus). Since this document is more about software than hardware, I won't go into the hardware decisions that created the memory layout. The ROM shows up in 4 locations, and the RAM is mirrored too. The ZX81 was designed to minimize the number of parts needed, so the memory layout reflects that design descision. This had to be connected to the expansion port on the back of the computer. For many, that was enough. They do not match the Datasheet pinouts of the respective RAM /BUSRQ 25 chips. yj7wnj, ldkhk, fs, uk, rvxj, cyd161, 79ig1gu, ls1jyz, lakqizn, pderq6,