The document discusses the main components inside a computer system unit, including the central processing unit (CPU) and memory. It describes how the CPU, which contains the control unit and arithmetic logic unit, interprets and executes instructions to process data from memory. The CPU communicates with memory and other components via input/output buses on the motherboard. Memory comes in volatile forms like RAM that temporarily store information, as well as non-volatile forms like ROM. The system unit also contains ports and connectors on the outside to attach peripheral devices.

1. Lecture No 4
System Unit
Central Processing Unit
RAM

2. What is the system unit?
A boxlike case that houses the
computer’s main hardware components

3. What are the different types of system units?
Desktops
Notebook
Personal Digital
Assistant

5. What’s inside the system unit?
Motherboard (mainboard)- Large circuit board with
thousands of electrical circuits
Power supply- provide electric power of all parts of the
system unit through main board.
Cooling fan- Keeps the system unit cool
Internal Speaker- Used for beeps when error is
encountered
Drive bays- Housing for the computer’s hard drive,
floppy drive and CD-ROM / DVD-ROM drives
Click N Learn

6. What’s on the motherboard?
Microprocessor (CPU)- Central processing unit interprets
and carries out instructions given by software
Memory- Enables the computer to retain information
Chipset- A collection of chips that provide the switching
circuitry needed to move data
Input/Output buses- Pathways that allow the
microprocessor to communicate with input and output
devices
Click N Learn

7. The Motherboard
Microprocessor
Keyboard /
Mouse Ports
Printer Port
Video Port
PCI Slots
(Peripheral
Component
Interconnect)
Memory Slots
AGP Slot
(Accelerated Graphics
Port)
Chipset

9. Central Processing UUnniitt ((CCPPUU))
The central processing unit, is the “brain” of computer system.
Administrative section of computer.
Supervises the operations of the other computer units.
CPU is connected to all other parts of computer.
Receives data and instructions given by user, processes
accordingly and produces the output.
This section not only executes the instructions but also controls
all the permanent or temporary storage of data, I/O activities as
well as the function of different devices attached with it.
It is further divided into two parts:
◦ Control Unit (CU)
◦ Arithmetic Logic Unit (ALU)

10. What are the types of CPUs?
Intel
Advanced
Micro Devices
(AMD)
Cyrix
Motorola (Apple)
Pentium IV
Pentium MMX
Pentium III

11. Basic Operation Performed by CPU
(Control Unit )
Intel
4 basic operations:
Fetch – The Control Unit takes the
instruction that is store in the Main
Memory.
Decode - The Control Unit
translates the instruction into machine
language or binary code.
Execute - carry out the command
Store - write the result to memory

12. Arithmetic and LLooggiicc UUnniitt ((AALLUU))
• Major processing unit of the CPU.
• All arithmetic and logical (decision making) activities are
performed in this section.
• Arithmetic means all sort of addition, subtraction, division and
multiplication.
• The logical operations performed in this unit make it possible for
computer to make decisions by comparing one item with the other.

13. Arithmetic and Logic Unit
Comparison (greater
than, equal to, or
less than)
Arithmetic
(addition, subtraction,
multiplication, and
division)

14. Machine Cycle
4 operations of the CPU comprise a
machine cycle.
Instruction time– time to fetch and decode
Execution time– time to execute and Store
e-time
i-time

15. Example
A Step student
1: The
control enters a unit
math
problem fetches the
into
math the memory problem
of
from the computer
memory
Step 2: 3: 4: The
ALU
results of the
math problem
are stored in
memory
The result in
memory
displays on the
screen of the
monitor
executes the
math problem
decodes the
and sends it to
the ALU

16. How a CPU works Click to
Control unit ALU
Memory
animate.
Click one
time only

18. What is memory?
A term for a device that enables the
computer to retain (store) information.

19. What are the types of memory?
Volatile memory (Random Access Memory/RAM;
Cache Memory; Virtual Memory)- Contents of
memory are erased when power supply is turned
off. Also called Temporary storage.
Nonvolatile memory (Read Only Memory/ROM;
Flash Memory)- Contents of memory are not erased
when power is turned off. Also called Permanent
storage.

20. What is Random Access Memory / RAM?
A type of volatile memory that stores
information temporarily so that it’s available to
the CPU.

21. HOW DOES RAM WORK?
CHIPS CONTAIN MEMORY LOCATIONS
CALLED MEMORY ADDRESSES
THE CPU STORES AND RETRIEVES DATA
BY GOING TO THE MEMORY ADDRESSES
Intel

22. WEB
KEYBOARD
CPU
RAM
MONITOR
CLICK TO BEGIN
ANIMATION
HOW RAM WORKS

23. What is cache memory?
Located within the CPU chip, it is the memory the
microprocessor uses to store frequently used
instructions and data.
Faster than RAM

24. What is virtual memory?
Part of the hard disk is reserved as RAM
When RAM modules become full the CPU
accesses the hard disk to store and retrieve
data
Slower than RAM
FUL
L

26. What are input/output (I/O) buses?
Pathways that enable the CPU to
communicate with input/output devices
Typically the buses contain slots
called expansion slots, in which
expansion cards are inserted
Expansion slots
Expansion card

28. What’s on the outside of the system unit?
Power switch- Located on the back; turns power on/off
to the computer
Receptacles- Called connectors or ports; Usually
located on the back; Used to plug in peripheral devices,
keyboard, mouse and monitor
Front panel- Contains drive bays, various buttons and
lights
BACK FRONT
Drive bays
On/off switch
Reset button
Indicator lights

29. Types of ports/connectors