1.3 System Software Vs Application Software

Generally speaking, a computer is a “deaf and dumb” machine, which cannot do anything at its own unless it is told to do so. We instruct it to do some number calculation, to create/modify a document, to work on some engineering application and so on. So this instruction (s) is the driving force that allows a computer to perform a certain task and known as “a program or a software”. It is it is this “software” that tells the machine’s physical components what to do and how to do.

The software falls into two major categories i.e. system software and application software. They are discussed as below:

1.3.1 System software

The system software basically manages and monitors the different resources f the whole computer system i.e. operating system, backup and restore utility program, drivers etc.

Operating system is the main and foremost part of the system software. It is discussed in chapter 7.

1.3.2 application software

Computer programs or application software is basically a set of programs that are used to accomplish a given task. It is basically designed and implemented by the computer users or different software houses. The application software is available in many forms/categories i.e. commercial software, scientific software, financial packages, games etc. a comprehensive discussion, about how to design and implement the software, is given under the topic “Systems Development” in section.


1.4 Basic Units Of Data Storage

The memory (main or secondary) is composed of an electronic circuitry, which is a combination of “On” and “Off” switches. This On/Off state has been conceived by the computer’s manufacturers as the numbers “1” and “0”, as the circuit can show 1 (on state) or 0 (off state) at a given time. Based of these two numbers i.e. 1 and 0 (the binary numbers), the computer can construct sophisticated ways of representing data in the memory. Thus, converting the numbers, alphabets, and characters (and their combinations) into binary digits enable us to represent them in the computer memory.

Basic Units Of Data Storage

1.4.1 Bit

The binary number 1 or 0 is called a bit (for binary digit), which is the basic unit fro storing data in the computer memory.  The circuit being on or off at a time,a bit in the memory is always storing some kind of data.

1.4.2 Byte

A byte is a combination of 8-bits, that can store a single character of data (a letter, numeral or special character). The capacity of the memory or the storage is expressed in terms of number of bytes it can hold or store. The following table shows the commonly used storage capacity terms:



No. of bytes (approx)

No. of bytes


K or KB




M or MB


About one million


G or GB


About one billion


T or TB


About one trillion

Table 1: Storage Capacity Terms

Example: convert 240 MB of memory in bytes and kilo-bytes?


Number of bytes in one Mb = equation_05

Total number of bytes in 240 MB = 240 *equation_06 bytes

Number of Kilo-bytes in one MB = equation_07 KB = 1024 KB

Total number of Kilo-bytes in 240 MB = 240 * 1024 KB

1.4.3 Word

A computer word, typically the size of a register, is defined as the number of bits that constitute a common unit of data, as defined by the computer system. The length of a word varies from computer to computer. Generally, the larger the word, the more powerful is the computer. The following table illustrates this factor:

No. of bytes/words

Number of bits

Era of computer

One byte


Very early personal computers
Two byte


Traditional micro-computers
Single word


Mainframes, some mini-computers, and some micro-computers
Double word (DW)


Super computers and some micro-computers

Table 2: Capacity vs Computer Era

Example: Convert 60 GB of memory into words?


Number of bytes in one GB = equation_08

Number of bytes in 60 GB = 60 * equation_09

Number of words in 4 bytes = 1 W

Number of words in 60 GB = 60/4 * equation_09

= 15 * equation_10 words

Remember that: An 8-bit machine could handle only one-byte (a character) at time, whereas a 64-bit machine handles two words or 8 bytes at a time, making its processing speed eight times faster.