What is assembler and interpreter?

Answer 1

There are two types of assemblers based on how many passes through the source are needed to produce the executable program.

• One-pass assemblers go through the source code once. Any symbol used before it is defined will require "errata" at the end of the object code (or, at least, no earlier than the point where the symbol is defined) telling the linker or the loader to "go back" and overwrite a placeholder which had been left where the as yet undefined symbol was used.
• Multi-pass assemblers create a table with all symbols and their values in the first passes, then use the table in later passes to generate code.

Answer 2

The job of an assembler is to convert low-level assembly language source into a given architecture's native machine code. We can think of machine code as being the common language of all machines, however every architecture has its own specific version of that language as dictated by the architecture itself. In order to produce the correct machine code for a given architecture, we need to use an assembler that was written specifically for that architecture. Moreover, the assembly language source needs to be written specifically for the assembler.

The assembly language for a given architecture is usually developed alongside the hardware and is an integral part of the hardware design. However it is the assembler that actually implements the language. The hardware developer will typically produce a base-line assembler and a specification to which all other assembler implementations must adhere. The base-line assembler executes upon the target machine and, in some cases (particularly in older hardware), is built-in to the machine architecture itself. However, other vendors are free to use that specification to produce their own assemblers, some of which will be intended to execute upon other machines thus making it possible for one machine type to produce machine code for another machine type.

Although assembly languages have much in common with each other, it's the differences that matter. Common instruction synonyms such as JNZ may be mapped to different opcodes, memory may be addressed differently, the number of available registers and their length may differ, and so on. Any change to the architecture requires a new assembly language and a new assembler to implement it.

The same applies to higher-level languages. Each implementation of a high-level language caters for a specific architecture. So although languages such as Java are extremely portable, this is only made possible because each machine architecture has its own dedicated implementation of the Java virtual machine (JVM) which translates portable Java byte code (the JVM's native code) into the machine's native code.

Answer 3

An assembler is a one type of compiler which compiles the program written in assembly language.

Answer 4

An assembler is a computer program for translating assembly language, basically a mnemonic representation of machine language into object code.