The components of thesystem unitLecture 20Zikria Mian
• System unit is the case that containselectronic components of a computer usedto process data.– Is available in a variety of shapes and sizes– The case of sytem unit is also known aschassis or casing• Keyboard, mouse, microphone, monitoretc are peripheral devices
The Components• Processor– Control unit – to manage instructions andinitiate appropriate tasks– Arithmetic Logic Unit (ALU) – to performarithmetic and logical operations– Registers – high speed storage locations totemporarily hold instructions / data– System clock (that sets the operating pace)
The Machine Cycle• For every instruction, the processor follows afour step cycle called the Machine Cycle– Fetching– Decoding– Executing– Storing• Some processors can execute one machinecycle at a time• Most modern computers support Pipelining
Processors comparison• Intel– Pentium, dual core…….• AMD– Athlonx2• IBM• MotorollaHeat control through Heat Sinks, Heat pipes andLiquid Cooling
Data Representation• Computer can only understand two discretestates, that is, On and Off represented normallyas 1 and 0• Computers use binary system and a bit is thesmallest unit of data.– 8 bits combine to make a byte and can represent 256individual characters– Several coding schemes are followed to representcharacters• ASCII• EBCDIC• Unicode (16-bit)
Types of Memory• RAM– Dynamic RAM– SDRAM (DDR2, DDR3)– Rambus DRAM (pipelining technology)– Static RAM– Magnetoresistive RAM
Types of Memory (contd.)• Cache– Memory Cache (L1, L2, L3)– Disk Cache• ROM• Flash Memory (Complimentary Metal-Oxide Semiconductors- CMOS)• Hard Disk
Expansion slots and Adapter Cards• Sound Card• Video Card• Modem• Network card• Plug and Play devices• RAM
Ports and Connectors• A port is a point at which a peripheral attaches tothe system unit. A connector joins a cable to therespective port.• Serial ports– That transfer one bit at a time• Parallel ports– That transfer more than one bit at a time• USB ports– Can connect upto 127 different peripherals with asingle connector• Special purpose ports• IrDA port / Bluetooth port
• BUS– Data transfers internally within the circuitryalong electircal wires. Each wire is called abus.– Data Bus– Address BusEach bus has a particular width and clockspeed.
BAYS and Power Supply• The system unit usually has slots to installadditional drives like extra hard disk, DVDdrive etc• The power supply connects to themotherboard, monitor, disk drives. Usuallycomes with extra wires to allow installationof additional hardware.