I/O shared memory

Several devices include their own memory called I/O shared memory
The I/O shared memory can be accessed by means of the usual mov instructions by sacrificing part of the programmer's address space
ISA bus: 0xe00000-0xffffff are reserved addresses (the well known 640KB-1M hole)
PCI bus: addresses close to the fourth GB are reserved for several PCI devices

Several devices include their own memory called I/O shared memory