What are assembly and machine languages?

Answer 1

Machine language is the native language of the machine. Every machine type has its own version of machine code, determined by the processor architecture. As such, code for a particular architecture cannot execute on a machine with a different architecture; in other words, machine code is non-portable.

Assembly language is a human-readable version of machine code. Each instruction (or opcode) maps to an easy to remember mnemonic such as MOV (move), ADD (addition), SUB (subtract) and so on. In this way the programmer doesn't have to remember the binary value of each opcode. Binary values themselves, such as memory offsets, can also be encoded using more convenient notation such as hexadecimal while decimal values and character information can be entered as literals. Due to its low-level nature, assembly language source code needs to be heavily commented to assist the reader. In order to produce the required machine code, the assembly language source code must be converted to a machine code executable. This is achieved using a relatively simple program known as an assembler. However, as with machine code itself, assembly languages are machine-dependent and non-portable.

To create portable code, you need to use a high-level language that is suitable for cross-platform development. When we talk about low-level or high-level programming languages, we're really talking about the amount of abstraction between the human-readable source code and the resultant machine code. High level languages are highly abstract, such that a single high level statement may produce dozens of low-level machine instructions. When writing code in assembly, each instruction has to be written in painstaking detail by hand. Unlike assembly languages which must be assembled, high-level languages are either compiled or interpreted. A compiled language produces a standalone machine code executable (similar to that produced by an assembler) whereas interpreted languages require a runtime program to convert and execute high-level statements one statement at a time. Some languages, like Java, compile to byte code rather than machine code. The byte code then has to be interpreted to produce the machine code but the byte code is portable. Java uses the Java virtual machine to perform the interpretation.

With high-level languages like C++, it is rarely necessary to use anything less abstract because C++ language compilers are capable of producing highly optimised and more efficient machine code far more easily and more quickly than any human could. Unlike Java, which is only suitable for applications development, C++ can be used to write any type of software, including low-level software such as drivers and operating system kernels. Prior to C++, this type of software would have been written in assembly language and/or C language.