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3.1 A MIX Machine Implementation.

The simulator implements the MIX machine as described in TAOCP, 1.3.1, p.120, Description of MIX. The machine is shipped with all external equipment, except the paper tape unit(1), and the floating point feature.

Each I/O device is bound to a particular UNIX file. By default the card reader is connected to stdin, the printer to stdout and the card punch to stderr. The typewriter is connected to stdin. The paper tape unit is not yet implemented.

The tape units use files ‘tape0’ to ‘tape7’ and the disk units use files ‘disk0’ to ‘disk8’ in the current directory. None of these files is required to exist: they will be created on demand, when the first output operation on the given unit takes place.

The disks are always opened for update without truncation, so that old data is not destroyed until it is overwritten. Note that big disk files will never shrink unless they are deleted.

In contrast, the tapes are always opened with truncation, so that any existing data is lost after the first OUT instruction is executed.

Footnotes

(1)

It will be implemented in future releases

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