Computer system organization

1. Unit I:
Computer Systems and Organisation
Class- XI (2020)

2. Chapter:1
Computer System Overview

3. Introduction to Computer System
A computer is an electronic device that can be programmed to accept data (input),
process it and generate result (output). A computer along with additional hardware
and software together is called a computer system.
A computer system primarily comprises a central processing unit (CPU), memory,
input/output devices and storage devices.

5. Input Devices Output Devices

6. Computer Memory
A computer system needs memory to store the data and instructions for
processing. Whenever we talk about the ‘memory’ of a computer system, we
usually talk about the main or primary memory. The secondary memory (also
called storage device) is used to store data, instructions and results permanently
for future use.
1.3.1 Units of Memory
A computer system uses binary numbers to store and process data. The binary digits 0
and 1, which are the basic units of memory, are called bits. Further, these bits are
grouped together to form words. A 4-bit word is called a Nibble. Examples of nibble are
1001, 1010, 0010, etc. A two nibble word, i.e., 8-bit word is called a byte, for example,
01000110, 01111100, 10000001, etc.

8. Types of Memory
computers have two types of memory — primary and secondary.
(A) Primary Memory: Program and data are loaded into the primary memory before
processing. The CPU interacts directly with the primary memory to perform read or
write operation. It is of three types :-
(i) Random Access Memory (RAM)
(ii) Read Only Memory (ROM).
(iii) Cache Memory
(i) Random Access Memory (RAM)- RAM is volatile, i.e., as long as the power is
supplied to the computer, it retains the data in it. But as soon as the power supply is
turned off, all the contents of RAM are wiped out. It is used to store data temporarily
while the computer is working.
(ii) Read Only Memory (ROM):- ROM is non-volatile, which means its contents are not
lost even when the power is turned off. It is used as a small but faster permanent
storage for the contents which are rarely changed. For example, the startup program
(boot loader) that loads the operating system into primary memory, is stored in ROM.
(iii) Cache Memory:- RAM is faster than secondary storage, but not as fast
as a computer processor. So, because of RAM, a CPU may have to slow down. To speed
up the operations of the CPU, a very high speed memory is placed between the CPU
and the primary memory known as cache.

9. (B) Secondary Memory: Primary memory has limited storage capacity and
is either volatile (RAM) or read-only (ROM). Thus, a computer system needs auxiliary
or secondary memory to permanently store the data or instructions for future use.
The secondary memory is non-volatile and has larger storage capacity than primary
memory.
Examples of secondary memory devices include Hard Disk Drive (HDD), CD/DVD,
Memory Card, etc.

10. Hard Disk
Hard disks have a very large storing capacity of data.
The hard disk memories store information on one or more circular platters (or disks) which
are continually spinning. These rotation disks are coated with a magnetic material and
stacked with space between them. Information is stored on the surface of rotating disks by
magnetic heads as tiny magnetic spots.

11. See the working of a hard disk:
https://www.youtube.com/watch?v=NtPc0jI21i0

12. Mobile System organization

16. Software
Types of software
Software are the set of programs that governs the operation of a computer system
and make the hardware run.
Typically, there are two major classifications of software, namely System Software
and Application Software.
1. System Software: The software that controls internal computer operations is called
system software. In simple words, we can say that system software is an
inter-mediator or a middle layer between the user and the hardware. The system
software can further be classified in three categories :
(i) Operation System (ii) Language Processors (iii) Utilities
(i)Operating System: It is the most prominent example of System Software. It
is a collection of software that handles resources and provides general
services for the other applications that run over them. There are various types
of operating system such as real-time, embedded, distributed, multiuser,
single-user, internet, mobile, and many more. It is important to consider the
hardware specifications before choosing an operating system. Some examples
of Operating systems given below:

17. •Android
•iOS
•Linux
•Mac OS
•MS Windows
•Ubuntu
•Unix
(ii) Language Processors:- Language processors are software that convert source
codes into object code.
source code:- It refers to the program code written by a programmer in a high level
programming language (HLL) such as C,Java,C++, Python etc.
Object code:- It refers to a code usually in machine language or binary code, a
language that computer can understand easily and run on hardware.
There are three types of language processors : Assembler, Interpreter and compiler.
Assembler: The Assembler is used to translate the program written in Assembly
language into machine code.
Interpreter: It converts and executes instructions written in a computer program
line by line. Examples: Python, Perl
Compiler: It converts and executes instructions written in a computer program in
one go. Examples: C, C++, Java

18. (iii)Utility: Utility software is designed to aid in analyzing, optimizing, configuring
and maintaining a computer system. It supports the computer infrastructure.
Softwares like antiviruses, disk cleanup & management tools, compression tools,
defragmenters, etc are all utility tools.
2-Application Software:
An Application software is the set of programs necessary to perform operations for a
specific purpose like railway reservation, financial accounting, graphic design,
Multimedia and animation etc.

19. Q1- What is a software library?
Ans- A software library is a predefined and available to use, suit of data and
programming code in the form of prewritten code/functions/scripts/classes etc. that can
be used in the development of new software programs and applications.
For example Python comes equipped with many software libraries like:
1-NumPy(Numerical Puthon)
2- SciPy (Scientific Python)
3- Panda library
Q2- What is the function of memory? What are its measuring units?
Q3- What is the difference between RAM and ROM?
Q4- What is the role of CPU of a mobile system?
Q5- What is the difference between an interpreter and a compiler?
Q6- What is application software ? Why is it required?
*Note:- answers are sent in screenshots of the book.