CBSE Class 11 Computer Science Computing and Binary Operation Notes

Historically computer work human clerks who calculated in accordance with effective methods. The term computing machine used increasingly from the
1920s, refers to any machine that does the work of a human computer , i.e., any machine that calculates in accordance with effective methods. During the elate 1940s and early 1950s, with the advent of electronic computing machines, the phrase 'computing machine' gradually gave way simply to computer, initially usually with the prefix electronic or digital. This entry surveys the history of these machines .

Charles Babbage was Lucasian professor of Mathematics at Cambridge University from 1828 to 1839 (a post formerly held by Isaac Newton). Babbage's proposed difference engine was a specialpurpose digital computing machine for the automatic production of mathematical tables (such as logarithm tables, tide tables, and astronomical tables.
Babbage exhibited a small working model in 1822.
The Swedes George and Edvard Scheutz constructed a modified version of Babbage's Difference engine.

9.1.1 Introduction.

The modern digital computer or simply a computer is a general purpose electronic machine which can process a large amount of information at a very high speed. A computer can perform millions of computations in a few minutes. It can also perform arithmetical and logical
operations.

A computer has five major components :
(1) Input unit (2) Memory unit (3) Control unit
(4) Arithmetic logical unit (5) Output unit

(1) Input unit : The input unit is the means where the user communicates data or information to the computer.

(2) Memory unit : The memory unit stores instructions, data and intermediate results. It supplies, when required, the stored information to the other units of the computer.

(3) Control unit : The control unit controls all the activities in the computer by sending electronic command signals to other components of the computer.

(4) Arithmetic Logical Units (ALU) : ALU is the unit where the arithmetic and logical (e.g., less than, greater than) computations are carried out. Control unit and ALU taken together is called Central Processing Unit (CPU).

(5) Output unit : The output unit receives the stored result from the memory unit converts it into a form. The user can understand and produces it in the desired format.
A computer may have more than one input and output units. For example, printer and display screen are two different output units attached to the same computer.

9.1.2 Memory.

Our aim is to see how we can use the computer to solve some problems. For that purpose, it is useful to know a little more about main memory. From the users point of view, main memory can be thought of as a collection of compartments (or locations) as shown in fig. (i)
Each compartment is assigned a number called its address (starting with zero as shown in the fig. (ii). The total number of compartments gives us the size of the memory 

Each compartment of memory (as well as a register in ALU) consists of sub-compartments fig. (ii). Each sub-compartment can store either a zero or a 1. Any information to be stored inside a computer is put using zeros and 1’s. The digits 0 and 1 are called binary digits (bits in short). The acronym bit is formed by taking the letter b from the word ‘binary’ and the letters i, t from the word ‘digit’. Similarly, we have the acronym dit for decimal digit, hit for hexadecimal digit etc. The number system that uses only two digits is called binary number system.
Computers use binary number system for computation.