A one-byte field in page zero, currently at location 0003H, that can support a logical-to-physical device mapping for I/O. However, its implementation in your BIOS is purely optional and might or might not be supported in a given CP/M system. The IOBYTE is easily set using the command: STAT logical device = physical device The CP/M logical devices are CON:, RDR:, PUN:, and LST:; each of these can be assigned to one of four physical devices. The IOBYTE can be initialized by the BOOT entry point of the BIOS and interpreted by the BIOS I/O entry points CONST, CONIN, CONOUT, LIST, PUNCH, and READER. Depending on the setting of the IOBYTE, different I/O drivers can be selected by the BIOS. For example, setting LST:=TTY: might cause LIST output to be directed to a serial port, while setting LST:=LPT: causes LIST output to be directed to a parallel port. Abbreviation for kilobyte. See kilobyte.