Introduction to information systems T. Cornford, M. Shaikh is1 060 2013

4.4 Data technologies
Everything stored in a computer is data, and that includes programs, both 
systems software and applications. From the point of view of the storage 
devices of a computer, it is all the same. Data in a computer takes the form 
of binary patterns 
−
sequences of 1s and 0s. The one and the zero can be 
stored in terms of an electrical charge or a magnetic polarity. The technical 
details of such storage need not concern us. 
The basic unit of storage is the bit (one binary digit 
−
a 0 or a 1), but it 
is common to group 8 bits together as a byte. Bytes form the basis for 
measuring storage capacity, as in these approximations:
• a kilobyte (kB) 1000 = 10
3 
bytes
–
which is
close to 2
10 
(1024) bytes 
• a megabyte (MB) 1,000,000 = 10
6
bytes – which is close to 2
20
bytes 
(just over 1 million in decimal)
• a gigabyte – 10
9
bytes close to 2
30
• a terabyte – 10
12
bytes close to 2
40
• a petabyte – 10
15
bytes close to 2
50
kilobyte, megabyte, etc. should be abbreviated to kB, MB, GB, TB. MB and 
kB are often just left as M or K, etc.
Strictly speaking we should differentiate between quantities defined 
as powers of 2 and as powers of 10. Thus in the strict international 
definitions, 1 megabyte (1 MB) = 10
6 
while
1 Mebibyte (1 MiB) = 2
20
. 
However, most of the world uses megabytes and gigabytes without making 
any distinctions between powers of 2 or of 10.
Data in a computer can be of different types; for example: numeric data, 
textual data, graphical data (pictures), video, sound data, programs 
(program instructions). 

---

Chapter 4: Contemporary trends in information and communication technologies
55
Each form of data has its own way of using the raw storage capability 
(RAM or secondary storage). Just by looking at a pattern of 1s and 0s, 
it is not possible to tell what type of data is being stored, but once the 
type is known, then the pattern can be decoded. For example, the pattern 
01001011 represents the letter ‘K’ in the ASCII code for representing text; 
but it represents the decimal number 75 if this binary code is interpreted 
as a binary number. It might also represent the machine code instruction 
‘add’.
Text is stored in a computer according to standard systems of encoding 
– usually some version of the ASCII code. Each character is stored in one 
byte (made up of eight individual bits). Thus, a name and address of 80 
characters will use 80 bytes of storage. All the printing characters that you 
can generate from your keyboard have an equivalent representation in the 
ASCII code; in addition, there are some non-printing codes – such as end 
of line, backspace, line feed, etc.
Activity
A warehouse stores information on 3,000 products. Each product description comprises 
about 500 characters of data plus a photo of half a megabyte. How much disc space is 
needed to store this information? Express your answer in megabytes and kilobytes.