Types of Software

Firmware is software that is stored permanently inside a hardware device to make that device work. It is the lowest-level software on a computer.

Firmware sits between hardware and the operating system. Key facts:

• Stored in ROM (or a similar non-volatile chip) so it survives a power-off.
• Loaded before the operating system, the moment the computer is switched on.
• The most famous firmware is the BIOS (Basic Input/Output System), or its modern replacement UEFI, which runs the bootstrap that finds and loads the operating system from secondary storage.
• Other firmware lives inside printers, routers, hard drives, washing machines and many other devices.
• Firmware can sometimes be updated (a "firmware update"), but unlike apps it does not change every day.

Hardware → firmware → OS → application: the communication chain

A click in a word processor travels through several layers:

1. The user clicks a button in a word processor (application software).
2. The word processor asks the operating system to print the document.
3. The OS uses the device driver for the printer to format the request.
4. The driver speaks to the firmware in the printer, which controls the printer's mechanics.
5. The hardware in the printer puts ink on paper.

Information flows back the other way too: when the printer finishes (or runs out of paper), the firmware sends an interrupt up the chain so the OS, then the application, then the user can be told.