This copies the block of data one byte at a time. The codice_5 instruction causes the following codice_6 to repeat until CX is zero, automatically incrementing SI and DI and decrementing CX as it repeats. Alternatively the codice_7 instruction can be used to copy 16-bit words (double bytes) at a time (in which case CX counts the number of words copied instead of the number of bytes). Most assemblers will properly recognize the codice_5 instruction if used as an in-line prefix to the codice_6 instruction, as in codice_10.