1. Chapter 2

2. SYSTEM UNIT
A system unit is the part of a computer that houses the primary devices that perform operations and produce results for complex calculations.
System unit includes: the motherboard, CPU, RAM and other components.
System unit does not includes: the keyboard or monitor or any peripheral devices.
A system unit is sometimes called a box or main unit.

3. A system unit includes the following parts:
- Motherboard
- Processing Devices
- Memory Chips
- System Clock
- Buses
-Ports
-Expansion Slots and Cards

5. MOTHER BOARD

6. Mother Board It is the Main circuit board in system unit
Every component of the system unit connects to the mother board.
Contains chips, integrated circuits, and transistors
The CPU, memory, hard drives, optical drives, video card, sound card and other ports and expansion cards all connect to the motherboard directly or via cables.
Also called system board or main board

7. Processing Devices central processing unit (CPU) :
Interprets and carries out basic instructions that operate a computer
Also called the processor
contained on a single chip called the “Microprocessor”. The microprocessor has two basic components:
Arithmetic/Logic Unit (ALU)
Control Unit
# The speed of CPU measured by MHz or GHz

8. Arithmetic Logical Unit (ALU) :
Consist of electronic circuitry to perform :
-Arithmetic operations (addition(+) , subtraction(-), multiplication(*), division(/)..etc
-logical operations(and , or, not,..)
-comparisons operations (less-than<=) , (equal=)
Control Unit (CU) :
It directs the movement of signals between the memory and the Arithmetic-Logic Unit and between the CPU and input/output devices.

9. MEMORY There are basically 2 types of memory:-
Temporary storage area for operating system, application programs, and data
Consists of one or more chips on motherboard
Each byte stored in unique address
There are basically 2 types of memory:-
Primary
Secondary

10. MEMORY
Memory
Primary
RAM
ROM
Secondary CD
Floppy

11. Primary Memory There are 3 types of Primary memory :-
Primary storage (or main memory or internal memory), often referred to simply as memory, is the only one directly accessible to the CPU.
There are 3 types of Primary memory :-
RAM (Random Access Memory)
ROM (Read Only Memory)
CMOS.

12. RAM
1) This is the part of the computer that stores operating system software , software applications and other information for the CPU to have fast and direct access when needed to perform tasks. 2) The data in the RAM can be read or modified. Hence it is called read/write memory. 3) The data in most types of RAM is lost after the program is terminated or the computer is switched off.

13. RAM - Main memory is available in to types:
1-Dynamic Random Access Memory (DRAM)
2-Static Random Access Memory (SRAM)

14. ROM The two main characteristics of the ROM are:
1) Instructions in the ROM can be executed but cannot be changed, hence the name Read Only Memory.
2) These instructions are not erased when the computer is switched off . Its contents cannot be changed by users.
Example of ROM :
PROM ,EPROM,EEPROM.

15. MEMORY cont…
ROM
PROM
EPROM
EEPROM
1.Primary Memory
RAM
DRAM
SRAM

16. MEMORY cont…
2.Secondary Memory

17. COMPARE
Primary Memory
Secondary Memory
Fast
Expensive
Low capacity
Connects directly to the processor
Slow
Cheap
Large capacity
Not connected directly to the processor

18. EXPANSION CARDS AND SLOTS
The expansion card : An expansion card is an electronic circuit board that adds more functionality to a desktop computer.
Expansion card types
Video cards
Sound cards
Network cards
TV tuner cards
Modem cards

19. Expansion Cards Cont…
Video Card
TV Tuner Card
PCI Card

20. Peripheral Component Interconnect Express(PCIE)
2.Expansion Slots
Expansion slots are located on the motherboard, and openings on the back of the computer allow the ports on the cards that go in the slots to be accessed
Expansion slot Types
PCI Express
AGP
PCI
ISA
MCA
VLB
Express Card
Peripheral Component Interconnect Express(PCIE)

21. Expansion Slots Cont.. Industry Standard Architecture (ISA)
Accelerated Graphics Port (AGP)
PCI Local

22. Ports Connects external devices to system unit keyboard port USB port
serial port
monitor port
game port
network port
mouse port
parallel port
speaker port
microphone port

23. BUS
Channel that allows devices inside computer to communicate with each other
On the motherboard
System bus connects processor and RAM

24. POWER SUPPLY AND CABLE
A power supply unit (PSU): is the component that supplies power to the other components in a computer.
Desktop computers have a power supply unit located within the system unit .
Notebook computers use AC adapters and batteries that are typically located outside the system unit.

25. POWER SUPPLY AND CABLE
cables: are used to connect exterior to the system unit via the ports