Integrated components
The motherboard includes some on-board components, meaning that they are integrated into its printed circuitry:
- The chipset, a circuit which controls the majority of resources (including the bus interface with the processor, cache memory and random-access memory, expansion cards, etc.)
- The CMOS clock and battery,
- The BIOS,
- The system bus and the expansion bus.
What's more, recent motherboards generally include a number of onboard multimedia and networking devices which can be disabled:
- integrated network card;
- integrated graphics card;
- integrated sound card;
- upgraded hard drive controllers.
The chipset
The chipset is an electronic circuit whose job is to coordinate data transfers between the various components of the computer (including the processor and memory). As the chipset is integrated into the motherboard, it is important to choose a motherboard which includes a recent chipset, in order to maximise the computer's upgradeability.
Some chipsets may include a graphics or audio chip, which means that it is not necessary to install a graphics card or sound card. However, it is sometimes advised to disable them (whenever possible) in the BIOS setup and to install high-quality expansion cards in the appropriate slots.
The CMOS clock and battery
The real time clock (or RTC for short) is a circuit which synchronises system signals. It is made from a crystal which, as it vibrates, gives off pulses (called timer ticks) in order to keep the system elements running on the same time. The timer frequency (expressed in MHz) the number of times the crystal vibrates each second, i.e. the number of timer ticks per second. The higher the frequency, the more information the system can process.
When the computer is turned off, the power supply stops providing electricity to the motherboard. When the computer is turned on again, the system is still on the right time. An electronic circuit, called the CMOS (Complementary Metal-Oxyde Semiconductor, sometimes called the BIOS CMOS), saves some system information, such as the time, the system date, and a few essential system settings.
The CMOS is kept powered by a battery (a button battery), or a battery located on the motherboard. Information on the hardware installed in the computer (such as the number of tracks or sectors on each hard drive) are stored in the CMOS. As the CMOS is a form of slow storage, certain systems sometimes recopy the CMOS's content into the RAM (fast storage); the term "memory shadow" is used to describe this process of copying the data into RAM.
The "complementary metal-oxide semiconductor" is a transistor manufacturing technology, the latest in a long line which includes the TTL ("Transistor-transistor-logic"), the TTLS (TTL Schottky) (faster), or the NMOS (negative channel) and PMOS (positive channel).
The CMOS allows many complementary channels to run on a single chip. Compared with TTL or TTLS, CMOS is much slower, but it consumes far less energy, which is why it is used in computer clocks, which run on batteries. The term CMOS is sometimes incorrectly used to refer to computer clocks.
When the system time keeps getting reset, or the clock runs late, all that is usually necessary is to change the battery.
The BIOS
The BIOS (Basic Input/Output System) is the basic program used as an interface between the operating system and the motherboard. The BIOS is stored in ROM (read-only memory, which can not be rewritten), so it uses data contained within the CMOS to find out what the system's hardware configuration is.
The BIOS can be configured using an interface (named the BIOS setup), which can be accessed when the computer is booting just be pressing a key (usually the DEL key. In reality, the BIOS setup is only used as an interface for configuration; the data is stored in the CMOS. For more information, check your motherboard's manual.) 
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