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Power Supply The + 3. 3 V and + 5 V circuits supply power to all the electronic circuitry in the system (motherboard, adapter cards and disk drive logic boards), and through the port sockets on the motherboard that poke out through the rear of the case, to the peripherals that don't have their own power supply (e. g. keyboard, mouse). Power supplies are often overlooked, but are essential to the proper operation of your system which requires a good, steady supply of DC power at the appropriate voltages. These voltages must be constant, right up to the maximum current your system will draw under load. CPU The CPU (Central Processing Unit) is the brain of the system.
It executes all the program code from the operating system and the applications you run, and does most of the calculating and processing of data. It sends commands to direct the actions of all the other components in the PC and it manages the distribution of data to / from those various components. Inside the CPU are registers, arithmetic and logic units (ALU), a floating-point unit (FPU), control circuitry and cache memory. Registers are circuits designed to hold data so that it can be processed in some way by an ALU or the FPU. Cache memory is extremely fast, but small relative to the main memory.
Cache memory is used to store the current set of working data and code. So when the processor needs to read the next bit of data or code, usually it can retrieve it much faster from the cache. On occasions when it must recall data from the (slower) main memory, the CPU is forced to wait instead of getting on with other operations. The CPU is the fastest component in your system. It works hard only sometimes, maybe when you play a game involving 3 D graphics, or perhaps compile a very large program or run a very large spread-sheet; but most of the time it is just waiting for you to press the next key, or for the next bit of data to arrive from the Internet, through your modem. Main Memory or RAM (Random Access Memory) Memory is temporary storage where the processor can access program code and data.
It is temporary because any information stored there is lost when the system loses power or is rebooted. A low or high (on or off) voltage state in those small circuits represents a ' 0 ' or ' 1 ', which are the only two possible states of a binary digit (a 'bit'). The high and low voltage state of each circuit is constantly refreshed. While you work on your computer, all your work is stored here until it's saved to the hard disk or other storage device. This is why it is important NOT to have any interruption to your power supply. Motherboard As its name implies, everything inside your PC (apart from the disk drives and power supply unit) is part of the motherboard, or sits in a socket on the motherboard, or is connected to it by cables (e.
g disk drives and power supply). So it plays an important structural role. Boiling it down to its essentials, the motherboard comprises the chipset, Super I/O chip, BIOS ROM, communications pathways called buses and a whole lot of sockets to plug things into. The chipset, usually a pair of chips, determines a lot of the features of your system. For example it determines what type of CPU and memory you can use. The chipset provides controllers for the buses and transfers data from one bus to another.
These controllers are referred to as the North Bridge and South Bridge, unless the manufacturer uses some proprietary name for marketing purposes. The North Bridge connects to the faster buses and the South Bridge to the slower buses. (If you are keen to learn about that, the box below contains a more detailed description. ) Other functions can also be integrated into the motherboard and as I wrote at the beginning there is a trend for motherboards to be designed in this fashion. The most common are integrated video and audio adapters. This can save most of the cost of an adapter card, but the performance is usually at the lower end of the spectrum. Video Adapter Card The main components on this card are some video memory, a video processor and a digital-to-analog converter. The computer's CPU and video processor work together to generate a digital representation of an image and store it in the video memory.
More advanced video processors will speed up the rendering of 3 D images in graphics applications and games by taking on some of the processing that the CPU would otherwise have to do. The digital-to-analog converter continuously reads through memory containing the image and generates the analog electrical signal that your monitor needs, on order to display the output from your computer. Hard Disk Drive The function of the hard disk drive is to provide convenient persistent storage for data and programs. By persistent I mean that the information will survive when the power to the computer is turned off.
Hard disks provide convenient storage for large amounts of data as it is always accessible. You don't have to find and insert the next floppy disk, or data storage tape. Be aware that hard drives do not provide permanent storage. Lots of things can go wrong and your data can be lost. You simply must look at it this way... If you don't backup your data, obviously you don't really want it!
It can and ultimately will be lost without warning. Binary data is written to the disk by magnet ising small areas with fields of two different directions. The head will produce a voltage pulse as it passes over the junction between areas of different field direction and in this way data can be read. There are two heads for each disk: one for each side. Each head is connected to an actuator arm that can swing out over or below the disk so that the head can hover over any point between the centre and the edge of the disk while it is spinning. All the arms are ganged together and move as one, so that only one head is writing or reading at any time.
All the above is enclosed within a sealed unit. The remaining element of a hard drive disk unit is the disk controller. This is a circuit board with all the electronics required to control the motor and the actuator arm assembly. It also produces the voltage waveform applied to the heads to write data and decodes the waveform generated by the head when reading data, as well as handling communications with the motherboard. Hard disk drives are slower than memory but faster than any other type of drive. After the Internet, waiting for my hard drive is the delay I notice most on my system.
The red LED on the front of your case indicates the drive is in use. Floppy Disk Drive The floppy disk drive works on the same principals as a hard disk drive, however it cannot record at such high data densities as the hard disk drive. This is because of the nature of the disk material, and because it is not rigid, nor fixed to the drive motor. Floppy disks are made of Mylar coated with a magnetic material and enclosed in a rigid plastic case. Earlier floppy disks were larger and had a much more flexible plastic case.
They were truly floppy and could easily be damaged. Floppy disk drives are the slowest type of disk drive you can get. CD-ROM Drive CD-ROMs encode data by having small areas either strongly reflective to light or non-reflective to light. To read this data, a CD-ROM drive employs a laser diode to emit an infrared light beam which is reflected onto a track on the CD-ROM by a mirror that is positioned by a motor. The light reflected by the disc is gathered and directed by a system of lenses to a photo detector that converts the reflected light pulses into an electrical signal, which is then decoded by the drive electronics and sent to the motherboard.
These devices are slower than hard disks, but much faster than floppy disks. Sound Card A sound card converts digital data into an analog signal that can be used as input to speakers or headphones. It also does the reverse, taking a signal from a microphone or other audio equipment and converting it into digital data. A sound card usually also has a game port connection which enables you to use a joystick. Keyboard The keyboard is the primary device by which someone can input commands or data into a computer system.
Pressing down on a key closes a switch below the key. All the key switches are connected in an array, so that a processor inside the keyboard can identify which key has been pressed when a switch is closed. The processor then sends a signal along the cable to the motherboard containing a code for the key that has been pressed. Once you lift your finger off the key, the key switch opens and the keyboard processor sends another signal with a code to indicate the release of the key. Mouse You will have seen the mechanical part of a mouse if you have ever removed the ring shaped plate from its underside to clean out the dust and dirt it collects. A ball sits on the plate and rests against two rollers that are arranged at a 90 degree angle to each other.
Connected to the rollers are wheels with spokes protruding from them. As your hand moves the mouse, the ball rolls across the surface the mouse is resting on and rotates the rollers and their attached wheels. The spokes on these wheels interrupt infrared light from an LED. Small optical sensors detect the interrupted pattern of light and thus the movement of the wheels. Each roller / wheel combination picks up movement along one of two perpendicular axes.
The simple circuitry inside the mouse transmits this movement information and the status of the buttons, which are simple contact switches, to the motherboard. Figure 6. Underside of a mouse with the ball cover removed.
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