1. Software

2. Systems Software Computers require two types of software
Applications software ;
such as word processing, spreadsheet or graphics packages
Operating systems software :
to control and monitor the running of application programs, and allow users to communicate with the computer

3. Functions of an operating system
Memory management.
Resource allocation and scheduling
Backing store management
Interrupt handling
Allowing a user to communicate with the computer

4. Utility programs
As well as the basic operating system, the systems software available to users includes numerous utility programs, such as:
Virus checkers - check disks and memory for viruses and delete them if detected;
Security and accounting software - checks user IDs and passwords, counts and reports the number of attempts made to log on under each user ID, the amount of processor time used at each session, total login time and so on;

5. Utility programs (continued)
File management utilities - attempt to repair corrupted files, reorganise files on disk so that free space is ‘defragmented’, ‘zip’ (compress) files so that they occupy less space.

6. DOS (Disk Operating System)
tells the computer how to format, read and write information on disk (either floppy or hard)
manages peripheral devices such as printer and keyboard
controls the execution of application software
Also specifies
how many files can be held in a disk directory
what is an acceptable file or directory name
the number of bytes that can be on a disk
the amount of memory usable by a program

7. Command-driven interface eg DOS
The user had to type in commands in exactly the correct syntax to perform any operation
This allowed complex commands to be entered to customise the operating system for a particular user
Experienced users could perform operations faster using DOS than by using a mouse and menus or icons in a Windows interface
1.   Each digit of the code number is assigned a ‘weight’. The right hand (least significant) digit is given a weight of 2, the next digit to the left 3 and so on.
2.   Each digit is multiplied by its weight and the products added together.
3.   The sum of the products is divided by 11 and the remainder obtained.
4.   The remainder is subtracted from 11 to give the check digit. The two exceptions are:
If remainder is 0, check digit is 0, not 11
If remainder is 1, check digit is X, not 10
Example:
To calculate the check digit for the number 1587:
Original code number
Weights
Multiply digit by its weight
Add products together = 63
Divide by remainder 8
Sub remainder from = 3
Check digit = 3. Complete code number is
To check that a code number is valid, it is not necessary to recalculate the check digit completely. If the check digit itself is assigned a weight of 1, and the products of the digits (including the check digit) and their respective weights are calculated, their sum will be divisible by 11 if the check digit is correct.

8. Operating Systems
DOS
Windows
Apple Macintosh (MacOS)
UNIX
Linux

9. Systems software Operating system Utility programs
perform common useful tasks such as search for lost files, sort files of data into a particular sequence, copy disk files to magnetic tape for backup purposes and so on.
Programming language compilers / interpreters
are different types of program used to translate the statements in a programming language such as Pascal, Visual Basic or C into a form that the computer can understand.

10. Systems software (continued)
Performance monitoring software
is used to monitor, analyse and report on the performance of a computer and its components. It can provide information such as the overall utilisation of the processor and number of disk accesses over a given period of time.
Communications software
In a mainframe environment, this is executed on a separate, dedicated processor (‘front-end processor’) and controls the flow of data to and from remote locations.

11. Applications software
Written to perform specific tasks
such as order entry, payroll, stock control or hospital appointments
May be designed specifically for a company
(‘bespoke software’) and written especially for them using a programming language or software such as a database management system
Alternatively, the software may be purchased ‘off the shelf’

12. General purpose software
Includes all common application packages such as:
word processing
desktop publishing
spreadsheet
database
computer-aided design (CAD)
presentation graphics.
Most general purpose software is sold as a package, including a CD containing the software and manuals to help you get started and to be used as a reference.

13. Productivity tools used by organisations include Integrated packages
WP, SS, DBs
Presentation Graphics (Powerpoint)
Communications
Integrated packages
combine features from all five of these
once very popular because they offered capabilities from all these packages in a single product at a relatively low price, and data could be transferred between applications. However, have fewer and less sophisticated features than are found in separately purchased packages.

14. Productivity tools (continued)
Software suites
offer four or more products packaged together
cheaper than buying the packages separately
e.g. Microsoft Office includes Word, Excel, Access, a multimedia presentation graphics package called PowerPoint and Microsoft Mail.
Lotus SmartSuite