[[Category:Computer Architecture]][[Category:Assembly Language]]''Assembly language'' is a [[Symbol|symbolic]] representation of [[Machine Language|machine language]]. It is therefore very [[Portable|architecture-specific]].

Each instruction is represented by a short mnemonic word such as "LDR" for ''Load Register'', "MOV" for ''move'', or "MUL" for ''multiply'', followed by (optional) arguments. The [[Addressing Mode|addressing mode]] is implied by the format of the arguments. Different [[Assembler|assemblers]] use slightly different syntax.

Here is a "Hello, World!" program written for an x86_64 Linux system using the [https://sourceware.org/binutils/docs/as/ GNU Assembler (gas/as)] syntax (which is the main assembler used in x86 assembler open source projects such as the Linux kernel, as well as the [[SPO600]] course), using Linux [[Syscalls]]:  .text .globl _start _start: mov $len, %edx /* file descriptor: 1 is stdout */ mov $msg, %ecx /* message location (memory address) */ mov $1, %ebx /* message length (bytes) */ mov $4, %eax /* write is syscall #4 */ int $0x80 /* invoke syscall */ mov $0, %ebx /* exit status: 0 (good) */ mov $1, %eax /* kernel syscall number: 1 is sys_exit */ int $0x80 /* invoke syscall */ .data msg: .ascii "Hello, World!\n" len = . - msg Here is a similar program for a Linux 32-bit x86 system, using the [http://www.nasm.us/xdoc/2.11/html/nasmdoc1.html#section-1.1 Nasm ] syntax:

Here Notice that the order of the arguments in some lines is reversed between the two assemblers, and the same program with GNU Assembler (gas/as) syntax:prefixes to symbols and values also change. 

This is written in [https://sourceware.org/binutils/docs/as/ GNU assembler Assembler (gas / as) ] syntaxusing Linux [[Syscalls]]:

mov %r0, $1 /* file descriptor: 1 is stdout */ ldr %r1, =msg /* message location (memory address) */ ldr %r2, =len /* message length (bytes) */ mov %r7, $4 /* write is syscall #4 */ swi $0 /* invoke syscall */

mov %r0, $0 /* exit status: 0 (good) */ mov %r7, $1 /* kernel syscall number: 1 is sys_exit */ swi $0 /* invoke syscall */

.ascii "Hello, world!\n" len = . - msg  === ARM (64-bit) - AArch64 === This is also in [https://sourceware.org/binutils/docs/as/ GNU Assembler (gas/as)] syntax using Linux [[Syscalls]]:  .text .globl _start _start: mov x0, 1 /* file descriptor: 1 is stdout */ adr x1, msg /* message location (memory address) */ mov x2, len /* message length (bytes) */ mov x8, 64 /* write is syscall #64 */ svc 0 /* invoke syscall */ mov x0, 0 /* status -> 0 */ mov x8, 93 /* exit is syscall #93 */ svc 0 /* invoke syscall */ .data msg: .ascii "Hello, world!\n" len = . - msg  === 6502 === Here is the same "Hello World" program in [[6502]] assembler as used in the [[6502 Emulator]], using the [[6502_Emulator#ROM_Routines|ROM routines]] for output:  define SCINIT $ff81 ; initialize/clear screen define CHROUT $ffd2 ; output character to screen JSR SCINIT ; clear screen LDY #$00 ; set Y index to zero loop: LDA msg,Y ; get a character BEQ done ; quit if character is null JSR CHROUT ; output the character INY ; increment index JMP loop ; get next character done: BRK ; break (stop program) msg: DCB "H","e","l","l","o",$2C,$20 DCB "W","o","r","l","d","!",$0d, $00 

=== External Examples =Resources ==

"Hello World" in many different types of assembler: * [[Assembler Basics]]* [http://leto.net/code/asm/hw_assembler.php"Hello World" in many different types of assembler]* [[x86_64 Register and Instruction Quick Start]]* [[aarch64 Register and Instruction Quick Start]]