The system unit contains the main electronic components of the computer. It includes a processor, memory, adapter cards, drive bays, and a power supply. The processor interprets and carries out instructions, and includes components like the control unit and arithmetic logic unit. Memory temporarily stores instructions, data, and results, and can be volatile RAM or nonvolatile ROM/flash memory. Additional components allow for expansion and connection of external devices like ports, buses, and bays. Regular cleaning of the system unit is important for preventing overheating and corrosion.

2. The system unit is a case that
contains electronic components of
the computer used to process data.

5. The system unit is composed
of:
Processor
Memory
Adapter Cards
Drive bays
Power supply

6. The Motherboard
It is the main board of the system
unit.

7. PROCESSOR
A. It is also called as central processing
unit (CPU). Its function is to interprets and
carries out the basic instructions that
operate a computer. There are three times of
processor:
1. Multi-core processor
2. Dual-core processor
3. Quad-core processor

8. Comparison of Personal
Computer Processors
The leading manufacturers of personal computer
processor chips are Intel and AMD. These
manufacturers often identify their processor chips by
a model name or model number. High-performance
desktop personal computers today use a processor
in the Intel Core family. Less expensive, basic
personal computers today use a brand of Intel
processor in the Pentium or Celeron family.

10. It is another
component of
the processor,
performs
arithmetic,
comparison, and
other
operation.
It is the
component of
the processor
that directs
and coordinates
most of the
operation on
the computer.
The Control Unit The Arithmetic Logic Unit
(ALU)

12. The System Clock
It is a small quartz crystal circuit
where the processor relies to control the
timing of all computer operations. It
generates regular electronic pulses, or
ticks, that set the operating pace of
components of the system unit.

13. Data Presentation

15. MEMORY
It consist of electronic components that
store instructions waiting to be executed
by the processor, data needed by those
instructions, and the results of
processing the data (information).

16. 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 programs that carry out a
specific task such as word processing ;
and
3. The data being processed by the
applications programs and resulting
information.

17. Bytes and Addressable
Memory
A byte (character) is the basic unit in
memory. Each byte resides temporarily in
memory in a location that has an address.
An address simply is a unique number that
identifies the location of the byte in
memory.

18. Memory Sizes

19. Types of Memory:
Volatile Memory
Temporary
RAM (Random
Access Memory)
Nonvolatile Memory
Permanent
ROM (Read Only
Memory
Flash memory

20. RAM (Random Access
Memory)
Also called as MAIN MEMORY
Consist of memory chips
It loses its contents when the power is
removed from the computer

22. Cache
Most of today’s computers improve processing times
with cache (pronounced cash). Two types of cache are memory
cache and disk cache. This chapter discusses memory cache.
Memory cache helps speed the processes of the computer
because it stores frequently used instructions and data.
Most personal computers today have at least two types of
memory cache: L1 cache and L2 cache. • L1 cache is built
directly in the processor chip. L1 cache usually has a
very small capacity, ranging from 8 KB to 128 KB. • L2
cache is slightly slower than L1 cache but has a much
larger capacity, ranging from 64 KB to 16 MB.
Current processors include advanced transfer cache, a type
of L2 cache built directly on the processor chip.
Processors that use advanced transfer cache perform at
much faster rates than those that do not use it. Personal
computers today typically have from 512 KB to 12 MB of
advanced transfer cache.

23. Read-only memory (ROM pronounced rahm) refers to
memory chips storing permanent data and
instructions.
Flash memory is a type of nonvolatile memory that
can be erased electronically and rewritten. Most
computers use flash memory to hold their startup
instructions because it allows the computer easily
to update its contents.
Some RAM chips, flash memory chips, and other
types of memory chips use complementary metal-
oxide semiconductor (CMOS pronounced SEE-moss)
technology because it provides high speeds and
consumes little power.

24. Memory Access Times
Access time is the amount
of time it takes the
processor to read data,
instructions, and
information from memory. A
computer’s access time
directly affects how fast
the computer processes
data. Accessing data in
memory can be more than
200,000 times faster than
access- ing data on a hard
disk because of the
mechanical motion of the
hard disk.

25. Expansion Slots and
Adapter Cards

26. Removable Flash Memory
Removable flash memory includes these
devices:
1. memory cards
2. USB flash drives
3. PC Cards/ExpressCard modules.

27. PORTS AND CONNECTORS
A port is the point at which a peripheral
attaches to or communicates with a system unit
so that the peripheral can send data to or
receive information from the computer.
A USB port, short for universal serial bus
port, can connect up to 127 different
peripherals together with a single connector.
Previously called an IEEE 1394 port, a 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, and DVD
drives, to a single connector. A FireWire port
allows you to connect up to 63 devices
together.

28. OTHER PORTS
Some ports not included in typical
computers but sometimes used are
Bluetooth,
SCSI,
eSATA,
IrDA, and
MIDI.

29. Port Replicators
and Docking
Stations
A port replicator is an
external device that
provides connections to
peripherals through ports
built into the device.
A docking station, which is
an external device that
attaches to a mobile
computer or device, contains
a power connection and
provides connections to
peripherals; it usually also
includes slots for memory
cards, optical disc drives,
and other devices

30. BUS, BAYS, POWER SUPPLY
A computer processes and stores data as a
series of electronic bits. These bits transfer
internally within the circuitry of the computer
along electrical channels. Each channel, called
a bus, allows the various devices both inside
and attached to the system unit to communicate
with each other.
A bay is an opening inside the system unit in which you can
install additional equipment.
The power supply is the component of the system unit that
converts the wall outlet AC power into DC power.

31. PUTTING IT ALL
TOGETHER
When you purchase a
computer, it is important
to understand how the
components of the system
unit work. Many components
of the system unit
influence the speed and
power of a computer. These
include the type of
processor, the clock speed
of the processor, the
amount of RAM, bus width,
and the clock speed of the
bus.

32. Over time, the system unit
collects dust — even in a clean
environment. Built up dust can
block airflow in a computer or
mobile device, which can cause it
to overheat, corrode, or even stop
working. By cleaning your computer
or mobile device once or twice a
year, you can help extend its life.
This preventive maintenance
requires a few basic products
(Figure 4-27):
• can of compressed air — removes
dust and lint from difficult-to-
reach areas; removes sticky liquid
spilled on keyboards
• lint-free antistatic wipes and
swabs • screen cleaning solution or
50/50 mix of rubbing alcohol and
water (do not use ammonia-based
solutions) • small computer vacuum
(or small attachments on your house
vacuum) • antistatic wristband — to
avoid damaging internal components
with static electricity • small
screwdriver (may be required to
open the case or remove adapter
cards)