S_370_IO

An S/370 machine uses several reserved memory locations when performing I/O operations.

CCW

CAW (Channel Address Word)

CSW

The SIO (Start I/O) instruction specifies the address of the device which will perform a write, read, read backward, control or sense operation.

The I/O operation code is contained in the first **CCW (Channel Command Word).** There may be multiple CCW's, "chained" together, e.g. for Dasd (disk) operations.

The CAW contains the address of the first CCW.