The System UnitThe system unit is a case that contains electroniccomponents of the computer used to process data. System units are available in a variety of shapesand sizes. The case of the system unit, sometimes called the chassis, is made of metal or plastic and protectsthe internal electronic components from damage. All computers and mobile devices have a systemUnit.
The Motherboard The motherboard, sometimes called a systemboard, is the main circuit board of the system unit. Many electronic components attach to theMotherboard, others are built into it.
Processor The processor, also called the central processing unit (CPU), interprets and carries out the basic instructions that operate a computer. The processor significantly impacts overall computing power and manages most of a computer’s operations. Most processor chip manufacturers now offer multi- core processors. A processor core, or simply core, contains the circuitry necessary to execute instructions. Processors contain a control unit and an arithmetic logic unit (ALU). These two components work together to perform processing operations.
The Control UnitThe control unit is the component ofthe processor that directs and coordinatesmost of the operations in the computer. it interprets each instruction issued bya program and then initiates the appropriateaction to carry out the instruction. Types of internal components that the controlunit directs include the arithmetic/logic unit , registers, and buses.
The Arithmetic Logic UnitThe arithmetic logic unit (ALU), another component ofthe processor, performs arithmetic, comparison, andOther operations. Arithmetic operations include basic calculations such asaddition, subtraction, multiplication, and division. Comparison operations involve comparing one dataitem with another to determine whether the first item
Machine CycleFor every instruction, a processor repeats aset of four basic operations, which comprisea machine cycle(1) fetching(2) Decoding (3) executing(4) storing
• Fetching is the process of obtaining a programinstruction or data item from memory.• Decoding refers to the process of translatingthe instruction into signals the computer canexecute.• Executing is the process of carrying out thecommands.• Storing, in this context, means writing the resultto memory (not to a storage medium).
RegistersA processor contains small, high-speed storagelocations, called registers, that temporarily holddata and instructions. Registers are part of the processor, not part ofmemory or a permanent storage device. Processors have many different types ofregisters, each with a specific storage function.
The System ClockThe processor relies on a small quartz crystalcircuit called the system clock to control thetiming of all computer operations.the system clock generates regular electronicpulses, or ticks, that set the operating pace ofcomponents of the system unit.Each tick equates to a clock cycle The pace of thesystem clock, called the clock speed, is measuredby the number of ticks per second
Processor Cooling Heat sinkspipes and liquid cooling technologies often are used to help dissipate processor heat. A heat sink is a small ceramic or metal component with fins on its surface that absorbs and disperses heat produced by electrical components such as a processor .
Memory• Memory consists of electronic componentsthat store instructions waiting to be executed.• Memory stores three basic categories of items 1-: the operating system and other• system software that control or maintain the computer and its devices .2-:application programsthat carry out a specific task such asword processing . 3-:The data being processedby the application programs and resultinginformation.
types of memory cache• L1 cache L1 cache usually has a very small capacity ranging from 8 KB to 128 KB. The morecommon sizes for personal computers are32 KB or 64 KB.• L2 cache L2 cache is slightly slower than L1 cache but has a much larger capacity, ranging from 64 KB to 16 MB.
Types of Memory ROM(Read only memory) ROM is nonvolatile, which means its contents are not lost when poweris removed from the computer. In addition tocomputers, many devices contain ROM chips.For example, ROM chips in printers containdata for fonts.
TYPES OF ROM There are two types of ROM1-:PROM2-:EEPROM
TYPES OF ROM• PROM (programmable read-only memory) A PROM chip is a blank ROM chip on which a programmer can write permanently. Programmers use microcode instructions to program a PROM chip.Once a programmer writes the microcodeon the PROM chip, it functions like aregular ROM chip and cannot be erased orchanged.
TYPES OF ROM EEPROM (electrically erasable programmable read-only memory) EEPROM chip, allows a programmer to erase the microcode with an electric signal.
Types of Memory Flash Memory Flash memory is a type of nonvolatile memory that can be erased electronically and rewritten, similar to EEPROM.
Types of Memory• CMOS(complementary metal-oxide semiconductor) (CMOS pronounced SEE-moss) technology because it provides high speeds andconsumes little power. CMOS technology uses battery power to retain information evenwhen the power to the computer is off. Battery-backed CMOS memory chips, for example, can keep thecalendar, date, and time current even when the computer is off. The flash memory chips that store a computer’s startup informationoften use CMOS technology.
Memory Access Times Access time is the amount of time it takesthe processor to read data, instructions, andinformation from memory.A computer’s access time directly affects howfast the computer processes data.
Expansion Slots and AdapterCards• Expansion Slots An expansion slot is a socket on the motherboard that can hold an adapter card.• Adapter Cards An adapter card, sometimes called an expansion card, is a circuit board that enhances functions of a component of the system unit and/or provides connections to peripherals.
Removable Flash Memory A type of memory which can easily insert and remove from a slot of a personal computer. A memory card is a removable flash memory device, usually no bigger than 1.5" in height orwidth, that you insert and remove from a slotin a personal computer, game console, mobiledevice, or card reader/writer.
Ports and Connectors• PORTS A port is the point at which a peripheral attachesto or communicates with a system unit so that theperipheral can send data to or receive informationfrom the computer.• CONNECTORSA connector joins a cable to a port. A connectorat one end of a cable attaches to a port on the system unit, and a connector at the other end ofthe cable attaches to a port on the peripheral.
Ports and Connectors• USB Ports A USB port, short for universal serial bus port, can connect up to 127 different peripherals together with a single connector. Devices that connect to a USB port include the following:mouse, printer, digital camera, scanner, speakers,portable media player, optical disc drive, smartphone, PDA, game console, and removablehard disk.
Ports and Connectors FireWire Ports FireWire port is similar to a USB port in that it can connect multiple types of devices that require faster data transmission speeds such as digital video cameras, digital VCRs,color printers, scanners, digital cameras, andDVD drives, to a single connector.
Ports and Connectors Bluetooth Port Bluetooth technology uses radio waves to transmit data between twodevices.A Bluetooth wireless port adapter that will convert an existing USB port into a Bluetooth port .
Ports and Connectors SCSI Port A special high-speed parallel port called a SCSI port, allows you to attach SCSI(pronounced skuzzy) peripherals such as disk drives and printers.
Ports and Connectors• eSATA Port• An eSATA port, or external SATA port, allows you to connect an external SATA (Serial Advanced Technology Attachment) hard disk to a computer. SATA hard disks are popular because of their fast data transmission speeds.• eSATA connections provide up to six times faster data transmission speeds than external hard disks attached to a computer’s USB or FireWire port .
Ports and Connectors IrDA Port IrDA port is used infrared signals to transmit data one device to another device. Devices that use IrDA ports include a smart phone, PDA, keyboard, mouse, and printer. Several of these devices use a high-speed IrDA port, sometimes called a fast infrared port.
Ports and Connectors• Serial Ports A serial port is a type of interface that connects a device to the system unit by transmitting data one bit at a time.• MIDI Port A special type of serial port thatconnects the system unit to a musical instrument , such as an electronic keyboard, is called a MIDI port.
Port Replicators and DockingStations Port Replicators A port replicator is an external devicethat provides connections to peripherals through ports built into the device. The mobile user accesses peripherals by connecting the port replicator to a USB port or a special port on the mobile computer.
Buses Buses are used to transfer bits from input devices to memory, from memory to the processor, from the processor to memory, and from memory to output or storage devices.
PARTS OF BUSES• There are two parts of buses• DATA BUS• ADDRESS BUS1-:Data Bus The data bus is used to transfer actual data.2-:Address Bus• The address bus is used to transfer information about where the data should reside inmemory.
TYPES OF BUSES• There three types of buses• System Bus• Backside Bus• Expansion Bus1-:System Bus• A system bus, also called thefront side bus ( FSB), is part of the motherboardand connects the processor to main memory.
TYPES OF BUSES2-:Backside Bus A backside bus ( BSB) connects the processor to cache.3-:Expansion Bus An expansion bus allows the processor to communicate with peripherals.