MIXAL

MIX registers

30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 09 08 07 06 05 04 03 02 01 00 (bit position) Registers ± A1 A2 A3 A4 A5 rA, Accumulator ± X1 X2 X3 X4 X5 rX, Extension Index registers   ± I1.4 I1.5 rI1, Index 1   ± I2.4 I2.5 rI2, Index 2   ± I3.4 I3.5 rI3, Index 3   ± I4.4 I4.5 rI4, Index 4   ± I5.4 I5.5 rI5, Index 5   ± I6.4 I6.5 rI6, Index 6 Program counter   J4 J5 rJ, Jump Condition code flags   O Overflow flag   <=> Comparison flag

MIX is a hypothetical computer used in Donald Knuth's monograph, The Art of Computer Programming (TAOCP). MIX's model number is 1009, which was derived by combining the model numbers and names of several contemporaneous, commercial machines deemed significant by the author. ("MIX" also represents the value 1009 in Roman numerals.)

The 1960s-era MIX has since been superseded by a new (also hypothetical) computer architecture, MMIX, to be incorporated in forthcoming editions of TAOCP. Software implementations for both the MIX and MMIX architectures have been developed by Knuth and made freely available (named "MIXware" and "MMIXware", respectively).

Several derivatives of Knuth's MIX/MMIX emulators also exist. GNU MDK is one such software package; it is free and runs on a wide variety of platforms.

Their purpose for education is quite similar to John L. Hennessy's and David A. Patterson's DLX architecture, from Computer Organization and Design - The Hardware Software Interface.

MIX is a hybrid binary–decimal computer. When programmed in binary, each byte has 6 bits (values range from 0 to 63). In decimal, each byte has 2 decimal digits (values range from 0 to 99). Bytes are grouped into words of five bytes plus a sign. Most programs written for MIX will work in either binary or decimal, so long as they do not try to store a value greater than 63 in a single byte.

A word has the range −1,073,741,823 to 1,073,741,823 (inclusive) in binary mode, and −9,999,999,999 to 9,999,999,999 (inclusive) in decimal mode. The sign-and-magnitude representation of integers in the MIX architecture distinguishes between “−0” and “+0.” This contrasts with modern computers, whose two's-complement representation of integer quantities includes a single representation for zero, but whose range for a given number of bits includes one more negative integer than the number of representable positive integers.

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Wikipedia