2. A computer system is a particular
type of system that its primary
purpose is that of performing
computations. Before the time of
the electronic computers, a
computer was a person that
performed computations.
A computer system is composed
of a Central Processing Unit
(Control Unit and Arithmetic &
Logic Unit), Memory and
Input/Output subsystems.
Computer Systems
4. CentralProcessingUnit(CPU)
The Central Processing Unit (CPU): is composed of a Control Unit and an
Arithmetic & Logic Unit.
The Control Unit (CU): controls the different components of the system and
it is responsible for fetching, decoding and executing the instructions of a
program.
The Arithmetic & Logic Unit (ALU): is performs arithmetic and logical
operations such as addition, division, comparison, etc.
Control Unit(CU)
The Control Unit is the part of the CPU that fetches (reads) instructions
from memory.
Each instruction is decoded to determine what exactly it is supposed to
do.
Once decoded, each instruction is executed.
5. The Arithmetic & Logic Unit (ALU) performs
the arithmetic operations as well as the
logical operations.
The arithmetic operations include addition,
subtraction, multiplication and division.
The logical operations are commonly used to
compare values and determine whether they
are greater, lesser or equal to one another.
These operations are normally carried out
with registers that are part of the CPU.
Arithmetic & LogicUnit(ALU)
10. Components of Computer:
Central Processing Unit
Buses
Memory Unit
Central Processing Unit
The part of the Computer that performs the bulk of data
processing operations is called the Central Processing Unit
and is referred to as the CPU.
Memory or Storage Unit:
Memory unit stores all the data and the instructions required for processing.
This unit can store instructions, data and intermediate results.
11. Main MemoryDevices
1. Random-Access Memory (RAM)
Usually called the main memory
It can be read and written to
It does not store information permanently (Volatile , when it is powered off, the
stored information are gone)
Information stored in it can be accessed in any order at equal time periods
(hence the name random access)
Information is accessed by an address that specifies the exact location of the
piece of information in the RAM.
12. PrimarystorageDevices
2. ROM (Read-Only-Memory)
A read-only-memory, non-volatile i.e. stores information permanently
Has random access of stored information
Used to store the information required to startup the computer
3. Cache memory
A very fast type of RAM that is used to store information that is most frequently
or recently used by the computer
Recent computers have 2-levels of cache; the first level is faster but smaller in size
(usually called internal cache), and the second level is slower but larger in size
(external cache).
13. SecondarystorageDevices
Secondary memory is also called secondary storage, external memory or non-
volatile. Secondary storage is a non-volatile memory which holds data and programs even
after electric power to the computer system has been turned off.. Data/Information is
stored permanently.
The kinds of secondary media are hard disks, solid-state storage, eMMC, USB, cloud
storage etc.
1. Hard Disk Drive (HDD)
Hard disks are typically used to store programs and very large data files. Using rigid metallic platters
and read/write heads that move across the platters
2. Solid-state drive (SSD)
solid-state storage does not have any moving parts, is more reliable, and requires less power. It saves
data and information electronically instead of magnetically or optical. SSD is faster than HDD.
14. SecondaryMemoryDevices
3. embedded Multi-Media Card (eMMC)
4. External hard disk
5. Flash memory/USB
6.Cloud storage: Data or files are said to be stored in cloud when
they are stored in a remote server which is easily accessible from
anywhere with internet access.
15. Exercises
(A)
1) Write down at least four input devices.
2) Write down a few examples of output devices.
3) Write down the types of primary storage devices.
4) Write down the types of secondary storage devices.
5) How many types of primary storage devices are there?
6) Which memory is also called as volatile memory?
7) What is the main function of Random Access Memory?
8) Write down any three secondary storage devices.
(B) Give the full forms for the following.
1) CU 2) ALU 3) RAM 4) ROM 5) HDD 6) SSD 7) eMMC
17. Exercises
(D) Choose the best option from the following.
1. Printer is an device .
a) output
c) Both
b) input
2. Keyboard is an example of device.
a) output b) input
c) network
3. One of the following is an output device .
a) RFID
c) Mouse
4. RAM is a memory.
a) volatile
c) both
b) Printer
b) Non-volatile
5. Hard disk memory.
a) volatile
c) both
b) Non-volatile
