Node:Input-output operators, Next:Conversion operators, Previous:Jump operators, Up:MIX instruction set
As explained in previous sections (see MIX architecture), the MIX computer can interact with a series of block devices. To that end, you have at your disposal the following instructions:
IN
OUT
IOC
JRED
JBUS
In all the above instructions, the MOD
subfile must be in the
range 0-20, since it denotes the operation's target device. The
IOC
instruction only makes sense for tape devices (MOD
=
0-7 or 20): it shifts the read/write pointer by the number of words
given by M
(if it equals zero, the tape is rewound)1.
In Knuth's original definition, there are other control operations available, but they do not make sense when implementing the block devices as disk files (as we do in MDK simulator). For the same reason, MDK devices are always ready, since all input-output operations are performed using synchronous system calls.