The system unit contains the main electronic components of a computer, including the processor, motherboard, memory, and storage devices. The processor performs instructions and calculations using components like the control unit, arithmetic logic unit, and registers. The motherboard connects the components and includes expansion slots for additional hardware. Peripheral devices like keyboards, mice, and monitors connect to the system unit but are not contained within the case.

1. The components of the
system unit
Lecture 20
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2. • System unit is the case that contains
electronic components of a computer used
to process data.
– Is available in a variety of shapes and sizes
– The case of sytem unit is also known as
chassis or casing
• Keyboard, mouse, microphone, monitor
etc are peripheral devices

4. The Components
• Processor
– Control unit – to manage instructions and
initiate appropriate tasks
– Arithmetic Logic Unit (ALU) – to perform
arithmetic and logical operations
– Registers – high speed storage locations to
temporarily hold instructions / data
– System clock (that sets the operating pace)

5. • Motherboard
MEMORYInput Devices Output Devices
Storage Devices
Processor

6. The Machine Cycle
• For every instruction, the processor follows a
four step cycle called the Machine Cycle
– Fetching
– Decoding
– Executing
– Storing
• Some processors can execute one machine
cycle at a time
• Most modern computers support Pipelining

7. Processors comparison
• Intel
– Pentium, dual core…….
• AMD
– Athlonx2
• IBM
• Motorolla
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9. Data Representation
• Computer can only understand two discrete
states, that is, On and Off represented normally
as 1 and 0
• Computers use binary system and a bit is the
smallest unit of data.
– 8 bits combine to make a byte and can represent 256
individual characters
– Several coding schemes are followed to represent
characters
• ASCII
• EBCDIC
• Unicode (16-bit)

10. Memory
• 1 KB = 1,024 bytes
• 1 MB = 1,048,576 bytes
• 1 GB = 1,073,741,824 bytes
• Two types of memories
– Volatile
– Non-volatile

11. Types of Memory
• RAM
– Dynamic RAM
– SDRAM (DDR2, DDR3)
– Rambus DRAM (pipelining technology)
– Static RAM
– Magnetoresistive RAM

12. Types of Memory (contd.)
• Cache
– Memory Cache (L1, L2, L3)
– Disk Cache
• ROM
• Flash Memory (Complimentary Metal-
Oxide Semiconductors- CMOS)
• Hard Disk

13. Expansion slots and Adapter Cards
• Sound Card
• Video Card
• Modem
• Network card
• Plug and Play devices
• RAM

14. Ports and Connectors
• A port is a point at which a peripheral attaches to
the system unit. A connector joins a cable to the
respective 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 a
single connector
• Special purpose ports
• IrDA port / Bluetooth port

15. • BUS
– Data transfers internally within the circuitry
along electircal wires. Each wire is called a
bus.
– Data Bus
– Address Bus
Each bus has a particular width and clock
speed.

16. BAYS and Power Supply
• The system unit usually has slots to install
additional drives like extra hard disk, DVD
drive etc
• The power supply connects to the
motherboard, monitor, disk drives. Usually
comes with extra wires to allow installation
of additional hardware.