Each position in the genomic sequence of a digital organism is one of 26 possible instructions. The table below shows the alphabetical code for each instruction, its mnemonic, and a brief description of its function.
| (a) | nop-A | No-operation instruction ; modifies other instructions |
|---|---|---|
| (b) | nop-B | No-operation instruction ; modifies other instructions |
| (c) | nop-C | No-operation instruction ; modifies other instructions |
| (d) | if-n-equ | Test if two registers contain equal values |
| (e) | if-less | Test if one register contains a lesser value than another |
| (f) | pop | Remove a number from a stack and place it in a register |
| (g) | push | Copy the value of a register onto the top of a stack |
| (h) | swap-stk | Toggle the active stack |
| (i) | swap | Swap the contents of two specified registers |
| (j) | shift-r | Shift all the bits on a register one to the right |
| (k) | shift-l | Shift all the bits on a register one to the left |
| (l) | inc | Increment a register |
| (m) | dec | Decrement a register |
| (n) | add | Calculate the sum of the values in two registers |
| (o) | sub | Calculate the difference between the values in two registers |
| (p) | nand | Perform a bitwise NAND on the values in two registers |
| (q) | IO | Output the value in a register and replace with a new input |
| (r) | h-alloc | Allocate memory for an offspring |
| (s) | h-divide | Divide off an offspring contained in memory (specified by heads) |
| (t) | h-copy | Make a copy of a single instruction in memory (specified by heads) |
| (u) | h-search | Find a pattern of nop-instruction in the genome |
| (v) | mov-head | Move a head to point to the same position as the flow-head |
| (w) | jmp-head | Move a head by a fixed amount stored in a register |
| (x) | get-head | Write the position of a specified head into a register |
| (y) | if-label | Test if a specified pattern of nops has recently been copied |
| (z) | set-flow | Move the flow-head to a specified position in memory |
From the Supplementary Information for an article by Lenski, Ofria, Pennock & Adami on "The Evolutionary Origin of Complex Features" that appeared in Nature (8 May 2003), vol 423, pp 139-144.