Diagnostic

A diagnostic is a piece of software which is designed to test the correct operation of some hardware. There are two main forms:

• Diagnostics which are used to verify that something is working properly.
• Diagnostics which are used to try and localize a fault, in order to repair it.

In many computers, the code in ROM which is used to boot the machine includes code to verify that it is correctly operating.

Such code is often written in assembler, so it can use as little as possible of the CPU to begin with; it then proceeds to test out each part of the machine (further instructions, etc) before using them.