[saagarjha]

> The Z80's system, although simpler, creates a "hole" in the memory, because the bottom of the memory space is used by ROM and therefore you cannot use the beginning of the memory space for normal RAM work.

Gameboy actually does a funny thing where the boot ROM gets mapped at the bottom of the address space, and then it writes to a MMIO address to unmap the ROM overlay and restore the first 256 bytes of the cartridge there instead. It’s quite amusing!

> On some computer platforms, the instruction pointer is called the "program counter", inexplicably abbreviated "PG"

Typo, maybe? Typically it’s called “pc”.

[Gordonjcp]

CP/M systems used to do that too, where the ROM would copy its important bits to upper memory and then swap itself out.