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Machine code or machine language is a set of instructions executed directly by a computer 's central processing unit CPU. Each instruction performs a very specific task, such as a load, a jump , or an ALU operation on a unit of data in a CPU register or memory. Every program directly executed by a CPU is made up of a series of such instructions. The phrase 'directly executed' needs some clarification; machine code is by definition the lowest level of programming detail visible to the programmer, but internally many processors use microcode or optimise and transform machine code instructions into sequences of micro-ops in a sophisticated way.
Numerical machine code i. While it is possible to write programs directly in numerical machine code, it is tedious and error prone to manage individual bits and calculate numerical addresses and constants manually. For this reason, programs are almost never written directly in machine code in modern contexts. The overwhelming majority of practical programs today are written in higher-level languages or assembly language. The source code is then translated to executable machine code by utilities such as compilers , assemblers , and linkers , with the important exception of interpreted programs,  which are not translated into machine code.
However, the interpreter itself, which may be seen as an executor or processor, performing the instructions of the source code, typically consists of directly executable machine code generated from assembly or high-level language source code. Every processor or processor family has its own machine code instruction set. Instructions are patterns of bits that by physical design correspond to different commands to the machine.
Thus, the instruction set is specific to a class of processors using mostly the same architecture. Successor or derivative processor designs often include all the instructions of a predecessor and may add additional instructions.
Occasionally, a successor design will discontinue or alter the meaning of some instruction code typically because it is needed for new purposes , affecting code compatibility to some extent; even nearly completely compatible processors may show slightly different behavior for some instructions, but this is rarely a problem.
Systems may also differ in other details, such as memory arrangement, operating systems, or peripheral devices. Because a program normally relies on such factors, different systems will typically not run the same machine code, even when the same type of processor is used.
A machine code instruction set may have all instructions of the same length, or it may have variable-length instructions. How the patterns are organized varies strongly with the particular architecture and often also with the type of instruction. Most instructions have one or more opcode fields which specifies the basic instruction type such as arithmetic, logical, jump , etc. Not all machines or individual instructions have explicit operands. An accumulator machine has a combined left operand and result in an implicit accumulator for most arithmetic instructions.
Other architectures such as and the xfamily have accumulator versions of common instructions, with the accumulator regarded as one of the general registers by longer instructions. A stack machine has most or all of its operands on an implicit stack. Special purpose instructions also often lack explicit operands CPUID in the x86 architecture writes values into four implicit destination registers, for instance. This distinction between explicit and implicit operands is important in code generators, especially in the register allocation and live range tracking parts.
A good code optimizer can track implicit as well as explicit operands which may allow more frequent constant propagation , constant folding of registers a register assigned the result of a constant expression freed up by replacing it by that constant and other code enhancements. A computer program is a sequence of instructions that are executed by a CPU. While simple processors execute instructions one after another, superscalar processors are capable of executing several instructions at once.
Program flow may be influenced by special 'jump' instructions that transfer execution to an instruction other than the numerically following one.
Conditional jumps are taken execution continues at another address or not execution continues at the next instruction depending on some condition. A much more readable rendition of machine language, called assembly language , uses mnemonic codes to refer to machine code instructions, rather than using the instructions' numeric values directly.
The MIPS architecture provides a specific example for a machine code whose instructions are always 32 bits long. The general type of instruction is given by the op operation field, the highest 6 bits. J-type jump and I-type immediate instructions are fully specified by op. R-type register instructions include an additional field funct to determine the exact operation. The fields used in these types are:.
Load a value into register 8, taken from the memory cell 68 cells after the location listed in register In some computer architectures , the machine code is implemented by an even more fundamental underlying layer called microcode , providing a common machine language interface across a line or family of different models of computer with widely different underlying dataflows.
This is done to facilitate porting of machine language programs between different models. With dataflow path widths of 8 bits to 64 bits and beyond, they nevertheless present a common architecture at the machine language level across the entire line. Using microcode to implement an emulator enables the computer to present the architecture of an entirely different computer.
Machine code is generally different from bytecode also known as p-code , which is either executed by an interpreter or itself compiled into machine code for faster direct execution. An exception is when a processor is designed to use a particular bytecode directly as its machine code, such as is the case with Java processors.
Machine code and assembly code are sometimes called native code when referring to platform-dependent parts of language features or libraries. The Harvard architecture is a computer architecture with physically separate storage and signal pathways for the code instructions and data. Today, most processors implement such separate signal pathways for performance reasons but actually implement a Modified Harvard architecture , [ citation needed ] so they can support tasks like loading an executable program from disk storage as data and then executing it.
Harvard architecture is contrasted to the Von Neumann architecture , where data and code are stored in the same memory which is read by the processor allowing the computer to execute commands. From the point of view of a process , the code space is the part of its address space where the code in execution is stored.
In multitasking systems this comprises the program's code segment and usually shared libraries. In multi-threading environment, different threads of one process share code space along with data space, which reduces the overhead of context switching considerably as compared to process switching. Pamela Samuelson wrote that machine code is so unreadable that the United States Copyright Office cannot identify whether a particular encoded program is an original work of authorship;  however, the US Copyright Office does allow for copyright registration of computer programs  and a program's machine code can sometimes be decompiled in order to make its functioning more easily understandable to humans.
Cognitive science professor Douglas Hofstadter has compared machine code to genetic code , saying that "Looking at a program written in machine language is vaguely comparable to looking at a DNA molecule atom by atom.
From Wikipedia, the free encyclopedia. What Kind of Code Is This? Retrieved February 23, An Eternal Golden Braid": Application binary interface ABI.
Binary code compatibility Foreign function interface Language binding Linker dynamic Loader Year problem. Types of programming languages. Assembly Compiled Interpreted Machine. Low-level High-level Very high-level. First generation Second generation Third generation Fourth generation Fifth generation. Retrieved from " https: Assembly languages Machine code. All articles with unsourced statements Articles with unsourced statements from March Wikipedia articles with GND identifiers.
Source code Object code Bytecode Machine code Microcode. Look up machine code in Wiktionary, the free dictionary.