Registers can hold up to 16 bits (1 word/2 bytes) of data.
ax bx cx dx can be accessed via high/low 8-bit (1 byte) portions.
General purpose registers
Arithmetic, add/subtract/compare
Segment registers
Read-only: cs, ip
Cannot be directly modified by a program
Can be indirectly modified by CPU instructions
| bits 15-8 | bits 7-0 | ||
|---|---|---|---|
| ax | 11111111 | 11111111 | 16-bit |
| ah | 11111111 | 00000000 | 8-bit |
| al | 00000000 | 11111111 | 8-bit |
| ax | ah | al | accumulator |
| cx | ch | cl | count |
| dx | dh | dl | data |
| bx | bh | bl | base: memory address |
| sp | stack ptr |
| bp | base ptr |
| si | source idx |
| di | destination idx |
| ds | data segment |
| es | extra segment |
| ss | stack segment |
| cs | code segment |
| ip | instruction ptr |