# What is MIXAL?

> MIXAL is the assembly language for Knuth's MIX computer: labels, local symbols, EQU, ORIG, CON and END, with a tiny example you can run in the browser.

**MIXAL**: MIXAL (MIX Assembly Language) is the symbolic assembly language Knuth defines for writing programs for the MIX computer.

**MIXAL**, short for MIX Assembly Language, is how programs for Knuth's [MIX](https://cracked.guide/glossary/mix) computer are written in The Art of Computer Programming. It turns readable lines like `LDA X` into MIX machine words.

## What a MIXAL line looks like

Each line has up to three parts: an optional **location** (a label), an **operation** (an instruction like `LDA` or a pseudo-operation like `EQU`), and an **address part**, which can carry an index register and a field: `LDA X,1(0:3)` loads bytes 0 to 3 of the word at X plus rI1 into register A.

The pseudo-operations are few: `EQU` defines a symbol, `ORIG` sets where the next word goes, `CON` and `ALF` place a constant or five characters, and `END` ends the program and names where it starts. **Local symbols** like `2H`, `2B` and `2F` let you reuse short labels for loops (the B means the nearest one before, F the nearest one after).

## A small example

This program adds the numbers 1 to 10 and halts with the sum in register A:

```
       ORIG 100
START  ENTA 0
       ENT1 10
LOOP   INCA 0,1
       DEC1 1
       J1P  LOOP
       HLT
       END  START
```

`ENT1 10` puts 10 in index register 1, `INCA 0,1` adds rI1 to A, and `J1P` jumps back while rI1 is positive. Paste it into the [MIX emulator](https://cracked.guide/mix) and step through it.

## Where it is taught

Knuth introduces MIXAL in [§1.3.2](https://cracked.guide/guide/knuth-w029-0), with worked programs for finding a maximum and printing a table of primes, annotated with how many times each line runs. Those counts are how he gets exact running times. The graded exercises at [/mix](https://cracked.guide/mix) follow the same section.

## Questions

### Is MIXAL the same as MIX?

No. MIX is the machine; MIXAL is the assembly language you write MIX programs in. An assembler turns MIXAL into MIX words.

### Can I run MIXAL online?

Yes. cracked.guide/mix assembles and runs MIXAL in the browser, and grades a set of exercises from TAOCP §1.3 when you are signed in.

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Source: https://cracked.guide/glossary/mixal
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