Assembly Language for Beginners

.1. X86

RCX/ECX/CX/CL

Byte number:

7th 6th 5th 4th 3rd 2nd 1st 0th

RCXx64

ECX

CX

CH CL

AKAcounter: inthisroleitisusedinREPprefixedinstructionsandalsoinshiftinstructions(SHL/SHR/RxL/RxR).

RDX/EDX/DX/DL

Byte number:

7th 6th 5th 4th 3rd 2nd 1st 0th

RDXx64

EDX

DX

DH DL

RSI/ESI/SI/SIL

Byte number:

7th 6th 5th 4th 3rd 2nd 1st 0th

RSIx64

ESI

SI

SILx64

AKA“source index”. Used as source in the instructions REP MOVSx, REP CMPSx.

RDI/EDI/DI/DIL

Byte number:

7th 6th 5th 4th 3rd 2nd 1st 0th

RDIx64

EDI

DI

DILx64

AKA“destination index”. Used as a pointer to the destination in the instructions REP MOVSx, REP STOSx.

R8/R8D/R8W/R8L

Byte number:

7th 6th 5th 4th 3rd 2nd 1st 0th

R8

R8D

R8W

R8L

R9/R9D/R9W/R9L

Byte number:

7th 6th 5th 4th 3rd 2nd 1st 0th

R9

R9D

R9W

R9L