What does BIOS mean?
BIOS is an acronym for Basic Input/Output System. It is the boot firmware program on a PC, and controls the computer from the time you start it up until the operating system takes over. When you turn on a PC, the BIOS first conducts a basic hardware check, called a Power-On Self Test or POST, to determine whether all of the devices that make up the motherboard or are attached to it are present and working. It then loads the operating system into your computer's random access memory, or RAM.
The BIOS also manages data flow between the computer's operating system and attached devices such as the hard disk, video card, keyboard, mouse, and printer.
The BIOS stores the date, time, and your system configuration information in a battery-powered non-volatile memory chip, called CMOS (Complementary Metal Oxide Semiconductor) after its manufacturing process.
Although the BIOS is standardized and should rarely require updating, some older BIOS chips may not accommodate new hardware devices. Before the early 1990s, it was not possible to update the BIOS without removing and replacing its ROM chip. Contemporary BIOS resides on memory chips such as "flash" chips or EEPROM (Electrically Erasable Programmable Read-Only Memory), so that you can update the BIOS yourself if necessary.
What is firmware?
Firmware consists of programs installed semi-permanently into memory, using various types of programmable ROM chips such as PROMS, EPROMs, EEPROMs, and flash chips.
Firmware is created, tested, and distributed like software. However, since installing firmware involves burning the programs into memory chips, you can usually only erase and rewrite firmware a limited number of times.
Firmware is non-volatile, and will remain in memory after you turn the system off.
Often, people use the term "firmware" to refer specifically to boot firmware, which controls a computer from the time that it is turned on until the primary operating system has taken over. Boot firmware's main function is to initialize the hardware and then to "boot" (load and execute) the primary operating system. On PCs, the boot firmware is usually referred to as the BIOS.
What is CMOS?
CMOS, short for Complementary Metal Oxide Semiconductor, is a low-power, low-heat semiconductor technology used in contemporary microchips, especially useful for battery-powered devices. Most commonly, though, the term CMOS is used to refer to small battery-powered configuration chips on motherboards of personal computers, where the BIOS stores the date, time, and system configuration details.
CMOS is the semiconductor technology used in the transistors that are manufactured into most of today's computer microchips. Semiconductors are made of silicon and germanium materials which, in a limited manner, conduct electricity. These materials are doped during manufacturing by adding impurities in order to become full-scale conductors of either extra electrons with a negative charge (N-type transistors) or of positive charge carriers (P-type transistors). In CMOS technology, both kinds of transistors are used in a complementary way to form a current gate that forms an effective means of electrical control. CMOS transistors use almost no power when not needed. As the current direction changes more rapidly, however, the transistors become hot. This characteristic tends to limit the speed at which microprocessors can operate.
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