== DRAM refresh ==
On Amstrad CPC, the Gate Array is responsible for the DRAM refresh, instead of using the Z80 built-in DRAM refresh mechanism. The reason is that there can only be 3 DRAM accesses per microsecond on this architecture. Also, doing Doing DRAM refresh on each M1 cycle as it is done on MSX would bog down the CPU speed on CPC given its bus arbitration scheme.
The Z80 generates a maximum of one request per microsecond. The CPC also requires two memory accesses per microsecond for reading video data.