**What is a BIT:**

—As we know a bit is
the smallest unit of data in a computer system

—A bit can either be a
12 or a 02

—This means that with
one single bit we can only represent only 2 different values

—12 =
110 and 02 = 010

**Representing Text, Pictures etc…**

—Text, pictures and
videos are also stored in a computer system using a sequence of binary digits

— Using one single bit
is not enough due to its small size

—If we want to store a
large quantity of data many more bits are required.

**Combining a number of Bits:**

—Each time a bit is
combined with another bit, more different combinations can be stored.

—If we will be using
two bits to store data, there are a total of 22=
4 different combinations

—Hence if we have 4
bits we would have 24= 16 different combinations

**Working:**

—With the following
number of bits how many combinations could be created?

1.5 bits

2.3 bits

3.6 bits

4.8 bits

Answers

1.5 bits = 25 Ã 32 combinations

2.3 bits = 23 Ã 8 combinations

3.6 bits = 26 Ã 64 combinations

4.8 bits = 28 Ã 256 combinations

**In the Early Days**

—When computers were first introduced they were simply used for performing calculations

—After a while scientists realized that computers can also be used to store and edit text in different ways

—The problem was that a computer could only understand binary (1s & 0s)

**BCD(binary coded decimal)**

—Very early memory codes.

—Each decimal number converted to binary equivalent individually.

—For example 39=0011 1001

—Each decimal digit is converted individually to four bit binary

—4 bits=>16 different characters.

—Only sufficient to represent 10 numbers.

—6 combinations are redundant.

**6 bit BCD**

—To represent other characters on keyboard 6 bit BCD is used.

—6 bits=> 64 different characters.

—Sufficient for 26 alphabet+28 special characters+ 10 digits.

—Can only present small letters.

—What about capital??

**EBCDIC**

—64 different BCD codes are not sufficient for all the English letters upper and lower.

—So Extended Binary coded decimal information interchange is used.

—Its 8 bit code=>256 different symbols.

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