Memory Address - Contents of Each Memory Location

Contents of Each Memory Location

Each memory location in a stored-program computer holds a binary number of some sort. Its interpretation, as data of some data type or as an instruction, and use are determined by the instructions which retrieve and manipulate it.

Some early programmers combined instructions and data in words as a way to save memory, when it was expensive: The Manchester Mark 1 had space in its 40-bit words to store little bits of data – its processor ignored a small section in the middle of a word – and that was often exploited as extra data storage. Self-replicating programs such as viruses treat themselves sometimes as data and sometimes as instructions. Self-modifying code is generally deprecated nowadays, as it makes testing and maintenance disproportionally difficult to the saving of a few bytes, and can also give incorrect results because of the compiler or processor's assumptions about the machine's state, but is still sometimes used deliberately, with great care.