Functions

CS Code Segment 16-bit number that points to the active code-segment
DS Data Segment 16-bit number that points to the active data-segment
SS Stack Segment 16-bit number that points to the active stack-segment
ES Extra Segment 16-bit number that points to the active extra-segment
Pointer Registers

IP Instruction Pointer 16-bit number that points to the offset of the next instruction
SP Stack Pointer 16-bit number that points to the offset that the stack is using
BP Base Pointer used to pass data to and from the stack
General-Purpose Registers

AX Accumulator Register mostly used for calculations and for input/output
BX Base Register Only register that can be used as an index
CX Count Register register used for the loop instruction
DX Data Register input/output and used by multiply and divide
Index Registers

SI Source Index used by string operations as source
DI Destination Index used by string operations as destination
Flags Register Abr. Name bit nº Description

OF Overflow Flag 11 indicates an overflow when set
DF Direction Flag 10 used for string operations to check direction
IF Interrupt Flag 9 if set, interrupt are enabled, else disabled
TF Trap Flag 8 if set, CPU can work in single step mode
SF Sign Flag 7 if set, resulting number of calculation is negative
ZF Zero Flag 6 if set, resulting number of calculation is zero
AF Auxiliary Carry 4 some sort of second carry flag
PF Parity Flag 2 indicates even or odd parity
CF Carry Flag 0 contains the left-most bit after calculations