Inside the System Unit

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Inside the System Unit
• System unit: The main case of a computer
• A system unit, also known as base unit, is the main body of a desktop computer. – Houses the processing hardware for a computer
– Also contains memory, the power supply, cooling fans, and interfaces to connect peripheral devices – Houses the drive bays in which storage devices (hard drives, DVD drives, etc.) are located – With a desktop PC, usually looks like a rectangular box Power Supply

• The power supply is a device [box] inside the system that converts A.C into D.C means changes normal household electricity into electricity that a computer can use. • The power supply has a fan that provides the system and components from overheating. The Motherboard

• Computer chip: A very small pieces of silicon or other semi-conducting material onto which integrated circuits are embedded • Circuit board: A thin board containing computer chips and other electronic components • Motherboard or system board: The main circuit board inside the system unit – All computer components must connect to the motherboard – External devices (monitors, keyboards, mice, printers) typically connect by plugging into a port exposed through the exterior of the system unit Central Processing Unit

• Small piece of semi-conducting material on which integrated circuits are etched. • It controls all the processing in a computer. Interprets and carries out basic instructions that operate a computer • It is also called brain of the computer. Or Processor. • Most PCs today use CPU chips (micro processor) of two kinds – those based on the model made by INTEL and MOTOROLA. Processing Speed

• CPU clock speed: One measurement of processing speed – Measured in megahertz (MHz) or gigahertz (GHz)
– Higher CPU clock speed = more instructions processed per second • Alternate measure of processing speed is the number of instructions a CPU can process per second – Megaflops, gigaflops, teraflops

• Other factors (CPU architecture, memory, bus speed, etc.) also affect the overall processing speed of a computer Typical CPU Components
• Arithmetic/Logic Unit (ALU): Performs integer arithmetic and logical operations • Floating Point Unit (FPU): Performs decimal arithmetic • Control unit: Coordinates and controls activities

• Prefetch unit: Tries to fetch data and instructions before they are needed • Decode unit: Translates instructions so they are understood by the control unit, ALU, and FPU • Internal cache and registers: Store data and instructions needed by the CPU • Bus interface unit: Where data and instructions flow in and out of the CPU Basic Components of the CPU

Basic Components of the CPU are:
• Control Unit
• Arithmetic/Logic Unit (ALU)
Arithmetic/Logic Unit (ALU)
• The ALU (Arithmetic Logic Unit) is an internal part of the processor which is used for all mathematical and logical operations, the basic operations of an ALU include adding and multiplying binary values as well as performing logical operations such as AND, OR etc. • The algorithms for performing these mathematical and logical operations are hard coded (stored permanently) within the ALU. Control Unit

• A control unit is the part of a CPU that directs its operation. It is responsible for controlling the activity of the rest of the computer. • It "directs the traffic" inside of the CPU – i.e. makes decisions & performs the functions of fetch, decodes, execute, and store. • The control unit can be thought of as the brain of the CPU itself. • It controls & decides how other parts of the CPU and in turn, rest of the computer systems should work in order that the instruction gets executed in a correct manner. CPU Machine cycle

• Machine Cycle is a four step process that the CPU performs to execute each machine level...
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