[ The PC Guide | Introduction to the PC | Overview
of Systems and Components ]
Motherboard and System Devices
The motherboard is the base of the modern computer
system. It is amazing how little attention this critical component gets in
mainstream circles, considering how much it does--though this situation is now improving,
fortunately. If the processor is the "brain" of the computer, then the
motherboard is the central nervous system and circulatory system, plus much more, all
rolled into one. Here are the main parts of the motherboard and its related devices:
- Motherboard: The motherboard is
the main circuit board in the computer where everything comes together. This is where you
plug in your processor, memory, cache, video card and other cards. It is also where you
connect your peripherals.
- System Chipset and Controllers: The chipset
and other motherboard circuitry are the "smarts" of the motherboard. Their job
is to direct traffic and control the flow of information inside the computer. These
circuits control the processor's access to memory, the flow of data to and from peripheral
devices and communications lines, and much more. The chipset is a critical part of any
computer, because it plays a big role in determining what sorts of features the computer
can support. For example, which processors you can use, which types of memory, how fast
you can run the machine, and what kind of system buses your PC can use, are all tied in to
the type of chipset the motherboard uses.
- System Buses: The system buses
are the electrical channels through which various parts of the computer communicate. The
physical part of these buses, the part you see, is the set of slots in the back of the
machine into which you put your video card, sound card and other cards. It is over the
system buses that your video card gets information from the processor, the processor saves
data to your hard disk, etc. The architecture chosen for each of the system buses has a
great impact on the performance of your PC, as well as dictating your choices for video
cards and other devices.
- BIOS: The system BIOS (which
stands for Basic Input/Output System and is pronounced "bye-oss" or
"bye-ose") is a computer program that is built into the PC's hardware. It is the
lowest-level program that runs on your computer. Its job is to act as an intermediary
between your system hardware (the chipset, motherboard, processor and peripherals) and
your system software (the operating system). By doing this, the operating system doesn't
have to be made different for every machine, which is why DOS will load on any PC. The
BIOS is what runs when you turn on your computer, and what loads your operating system
(for example, DOS). The BIOS also allows you to set or change many different parameters
that control how your computer will function. For example, you tell the BIOS what sort of
hard drives you have so it knows how to access them.
- Cache: The system cache is a
small, high-speed memory area that is placed between the processor and the system memory.
The value of the cache is that it is much faster than normal system memory. Each time the
processor requests a piece of data from the memory, the system first checks the cache to
see if the information is there. If it is, then the value is read from cache instead of
memory, and the processor can get back to work that much sooner. If it isn't, then the
data is read from memory and given to the processor, but it is also placed into the cache
in case the processor needs it again in the near future.
- System Resources: System resources
are not actual physical devices; they are nothing you can reach into the machine and
touch. But they are very important for two reasons. First, they dictate how your PC
organizes its access to various memory areas and devices. Second, they are one of the most
common areas where people have problems with the setup of their PCs: so-called resource
conflicts. These are the four types of resources that various parts of your computer can
sometimes decide to fight over:
- Interrupts (IRQs): As described in the example in the
chapter on how the PC works, a device requests time from the processor using these
interrupt requests. Under traditional designs, each device has a different IRQ number. If
two try to use the same one, a conflict can result. Newer technologies can allow multiple
devices to share an IRQ channel.
- Direct Memory Access (DMA) Channels: Some devices have the ability to read
and write directly from the system memory, instead of asking the processor to do it for
them. Cutting the "middle man" out in this manner improves the efficiency of the
system. Each device that does this needs its own DMA channel.
- Input/Output (I/O) Addresses: Devices exchange information with the system by
putting data into certain specific memory addresses. For example, when we pressed the
letter "M" in the example mentioned above, the keypress was stored in a certain
memory address until it was time for the processor to deal with it. Any time information
goes into or out of the machine, to your modem or hard drive or printer for example, it
uses these I/O addresses. Again, each device needs its own memory area.
- Memory Addresses: Similar to I/O addresses, many devices use blocks of memory as
part of their normal functioning. For example, they may map hardware programs (BIOS code)
into memory, or use a memory area to hold temporary data they are using.
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