IBM mainframe assembler is actually somewhat abstracted from the hardware. The original assembler is very CISC-like, but today it's running on RISC-like cores.

IBM mainframe assembler is actually somewhat abstracted from the hardware. The original assembler is very CISC-like, but today it's running on RISC-like cores. As for the hardware, I/O is done through channel programs, which can have any device as a backend - it's a generic way to do DMA. There is a lot of legacy stuff (like CCKD, VTAM) but more or less it's all emulated today by the hardware/software.