汇编语言和机器语言之间有什么关系？

Question

Are assembly language and machine language (for the same underlying system) really the same? Are there any differences between these two concepts?

Answer 1

Assembly language is a convenience mechanism over the machine language. With assembly language you use mnemonic sequences instead of numeric operation codes and can use symbolic labels instead of manually calculating offsets. It also protects you from really dumb errors - like typing a malformed processor instruction.

Otherwise the assembly language is the equivalent of the machine language. Sometimes you will have an old assembler that will not support mnemonics for some instructions of the newer processors - then you can still insert operation codes directly into the program.

Answer 2

Machine language is the "Bit encoding" of a CPU's opcodes.

Assembly langauge is the "Symbolic encoding" of a CPU's opcodes.

So for Example Symbolically:

loop:  dec R1    # Decrement register R1
       bnq loop  # Branch if not equal to zero to
                 # address "loop"

Becomes Bit encoding:

# Mythical CPU Machine code 4 bits operation,
#                           4 bit "option"
       0x41      # 4 is a "dec" and represents r1;
       0x7E      # 7 is bnq and E means PC -2;

Generally it's a one to one relationship, however some assembly languages will ocationally have extra assembly instructions that map to either multiple machine code instructions or reuse another opcode. Such as using machine code "xor R1,R1" as a "clr R1" or something very similar.

In addition assembly languages will tend to support "macro programming" which in the 80's when assembly was used extensively gave the source code a more "high level" appearance. I've personally written assembly macros that looked like "plot x,y" and "Hex Val" to simplify common operations.

For example:

# Mythically CPU Macro
.macro spinSleep x,y
            ld #x,y
localLoop:  dec y
            brq localLoop
.endmacro
# Macro invocation
            spinSleep 100,R1
# Macro expantion
            ld #100,R1
localLoopM: dec R1
            brq localLoopM   # localLoopM is "Mangled" for localization.

Answer 3

I found a really good explanation, thought to post it here, so that others could read it:

Machine language is the actual bits used to control the processor in the computer, usually viewed as a sequence of hexadecimal numbers (typically bytes). The processor reads these bits in from program memory, and the bits represent "instructions" as to what to do next. Thus machine language provides a way of entering instructions into a computer (whether through switches, punched tape, or a binary file).

Assembly language is a more human readable view of machine language. Instead of representing the machine language as numbers, the instructions and registers are given names (typically abbreviated words, or mnemonics, eg ld means "load"). Unlike a high level language, assembler is very close to the machine language. The main abstractions (apart from the mnemonics) are the use of labels instead of fixed memory addresses, and comments.

An assembly language program (ie a text file) is translated to machine language by an assembler. A disassembler performs the reverse function (although the comments and the names of labels will have been discarded in the assembler process).

Source : What is difference between machine language and assembly language?

Answer 4

In Assembly, instructions are easier-to-understand representations of CPU instructions.

But the assembler also makes, for example, addressing easier:

• In machine language you have to know the distance (in address space) between where you are and where you want to jump to
• In Assembly language you call one address "iWantToJumpHere" and then you can say "jump iWantToJumpHere"

This makes assembly much easier to maintain, especially when the distance between the addresses changes.

Answer 5

machine language is what the chip understands Assembly is what you understand

Every assembly instruction has a machine language equivalent. x86 has a few single-byte instructions, but they're variable length and can be up to 15 bytes long (including optional prefixes)

 machine code bytes |   x86 assembly language
8D B0 00 36 65 C4    lea    esi, [eax - 1000000000]     
BB 00 FC FF FF       mov    ebx, -1024
43                   inc    ebx
41                   inc    eax
3B CA                cmp    ecx,edx
C3                   ret

C5 F5 72 D2 01       vpsrld ymm1,ymm2,0x1        ; AVX2
C5 F5 D4 6D 88       vpaddq ymm5,ymm1,YMMWORD PTR [ebp-0x78]
C5 CD D4 AD 68 ff ff ff vpaddq ymm5,ymm6,YMMWORD PTR [ebp-0x98]

Answer 6

汇编级语言是通过允许程序员编写助记符而不是二进制代码（机器代码）来使编程变得简单的第一个有意识的步骤。

Answer 7

Machine Language:

1. It is the first generation programing language
2. It is much difficult than Assembly Language
3. Difficult to understand by the human
4. It is in the form of 0s and 1s
5. Machine Language varies from platform
6. It cannot be changed easily
7. It does not support modification
8. The risk of existence of error is high
9. Binary code is hard to memorize
10. No need of compiler

Assembly Language:

1. It is a second generation programming language
2. It is less difficult than machine language
3. Easy to understand by the human
4. It uses symbolic instructions, descriptive names for data items and memory location
5. The Assembly Language is platform dependent
6. It is easily Modifiable
7. It's support changes
8. The risk of occurrence of error is reduced
9. Memorability is high
10. It is needed compiler and knows as assembler

Answer 8

Assembly language is first converted to machine language by the assembler. which is stored in memory (RAM) processor/cup fetch it and store in from memory to register and follow the instruction set one after one.

Answer 9

Assembly Language is the symbolic encode of opcode (operation code) that is understand by humans and only use to instruct computer processor (hardware operation) and robot (robotic operation) to perform specific tasks. This is an understandable language to human. This language is only use to instruct hardware operation and definitely not use to create software programme. A assembler is use to convert this symbolic encode part of opcode (operation code) into machine language. Operation Code (Opcode) is a part of machine language.