The 8080 interrupt system is one of the most simple and straightforward. Instead of having sophisticated built-in mechanics, reacting to interrupts, the 8080 just accepts a single instruction from an external source, marking this cycle with INTA. This opens up many more possibilities for external interaction than fixed handling.
RSTx instructions ...
The Game Boy is an SoC; with the exception of the on-board work RAM
and video RAM (8 KB each), the CPU and all on-board peripherals are
contained on a single chip. (The cartridge adds external ROM and
optionally a memory bank controller, RAM and other peripherals.)
Thus, the HRAM is on the CPU die. Is not inherently faster than
external memory: all accesses ...