What is machine code? - Definition from Whatis.com
Machine code is the elemental language of computers, consisting of a stream of 0's and 1's. Ultimately, the output of any programming language analysis and processing is machine code. After you write a program, your source language statements are compiled or (in the case of assembler language) assembled into output that is machine code. This machine code is stored as an executable file until someone tells the computer's operating system to run it. (In personal computer operating systems, these files often have the suffix of ".exe".)

The computer's microprocessor reads in and handles a certain number of 0's and 1's at a time. For example, it may be designed to read 32 binary digits at a time. Because it is designed to know how many bits (and which bits) tell it what operation to do, it can look at the right sequence of bits and perform the next operation. Then it reads the next instruction, and so on.

In analyzing problems or debugging programs, a tool to use is a dump of the program. A dump is a printout that shows the program in its machine code form, but since putting it in 0's and 1's would be hard to read, each four bits (of 0's and 1's) are represented by a single hexadecimal numeral. (Dumps also contain other information about the computer's operation, such as the address of the instruction that was being executed at the time the dump was initiated.)

Contributor(s): Marianne Doig
This was last updated in November 1997

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