Topic 11 Software and Human Computer Interface

What is software?

The computer and its peripherals are called hardware.  Without software, hardware is useless. 

 You must remember that the computer can only do one thing, add two binary numbers.  The computer does not know anything.  It has to given instructions for absolutely everything it does.  These sets of instructions are called programs.  Software is a term that describes programs.  When you buy software, you are buying a suite of many programs that do a particular job.

 Question 1.  What is the difference between a program and software? ANSWER

There are two main categories of software:

• Systems software, concerned with running the computer and its peripherals
• Applications software, which is about getting the computer to do a particular useful job.

The systems software can be broken down into two further areas:

• The operating system;
• “Housekeeping” programs or utility programs to maintain the good order of the computer.  This include error detection programs, file management utilities and virus checkers.

The Need for an Operating System

The operating system is a set of programs that are provided when you buy a computer.  The operating system is needed for applications programs to run properly.  The operating system is loaded onto the hard disk and when you turn on the computer, it is loaded to the computer’s main memory.  This may take a couple of minutes.

The role of the operating system is to manage the computer’s resources do that it operates in the most efficient way.  It’s rather like the timetable of a school or college.  The students know what lessons they have to go to, but without a timetable, it would be hit and miss as to whether they got to the correct teacher.

The operating system of a PC is much simpler than that of a supercomputer.  Games computers have a specialist operating system.

All operating systems have the following functions:

• Memory management – if there are several programs open at the same time the operating system (OS) has to allocate memory to the programs that are open, as well as itself.  If a program is too big for the available memory, the OS will shunt part of other programs to the hard disk on a temporary basis and will return them to the memory when they are needed.  This can take a bit of time and increasing the main memory can make the computer operate faster.  This is called virtual memory.
• Resource allocation and scheduling – large computers might have several programs running at the same time.  The OS allocates processing time to each program.  You might not notice this as the processing is very fast.
• Backing store management – the OS looks after the transfer of data from main memory to the secondary stores and back again.  It maintains a directory of the disk to know where look up files.
• Interrupt handling – when you press the return key to set a step in a program going, you send a message called an interrupt to the CPU.  There are also interrupts for the printer, mouse, and other peripherals.  Each has a separate interrupt code, but sometimes they can clash, and that will result in a conflict, leading to the computer to crash.
• Allowing the user to communicate with the computer – a computer that didn’t do this would be pretty useless.  There may be instructions to start a program, or copy a file.  In a GUI system, this is done with a mouse.

 The programs that work directly with the CPU are referred to as the kernel.  The programs associated with the operating system, but not directly with the management of the CPU are called the shell.

The earliest PC’s had an operating system called DOS (Disk Operating System) produced by William Gates’ Microsoft Corporation.  At the same time PC’s made the MacIntosh Corporation had the Mac operating system that used the Graphical User Interface, which was much easier to use than Gates’ command line interface.  Also DOS only allowed one program to run at a time.

DOS soon adopted the windows approach with Windows 3.1, which enabled several programs to be run at once, multi-tasking.  The user could switch between tasks.  From this the concept of the desktop was born.  The idea was that users could have their most commonly used programs arranged on a screen called the desktop, just as they would on their desks in the office.

More superior operating systems were introduced with Windows 95, 98, 2000, ME, and XP.  These allowed users to:

• Multi-task

• Use long filenames

• Install new peripherals easily, using plug and play.  (That’s the theory, but many people still call it ‘plug and pray’.)

Question 2  Disk directories record information about files on disk.  State three items that are recorded.  ANSWER

The picture shows a modern operating system interface

 Windows XP has 35 million lines of code; it is the biggest program ever written.  The picture above shows a Windows XP desktop.

There are other operating systems such as Unix, written in the language C.   There are many programmers who write in C, which has a very machine efficient code.  The same software can be used on a variety of hardware that uses Unix.

Linux has a big advantage over Windows; most of it is free.  So you can download the operating system from the Internet.  Also, unlike Windows, it is virtually bug-free.  Where bugs are found, up dates are rapid.  It was developed by many of the best programmers in the world in an altruistic exercise by the Finnish programmer Linus Torvalds.  Programmers are allowed to alter the code to their hearts’ content, tailoring it to their own purposes.  Although there are not many programmes that operate with Linux, some software companies are now developing Linux versions of their software to break the monopoly enjoyed by Microsoft.  Linux does provide its analogous version of the Office Suite, which is again free.

Some web servers and some networks use a Linux operating system.  The layout is like very like Windows, for the normal work it as easy as Windows.

Linux has a few disadvantages:

• File system is different to windows;
• It is slightly slower.

Operating System software also has utility programs:

•  Security and accounting programs – to check user ID’s and passwords, as well as logging how many times users are logged on, and allocating processor time,

• File management programs – these include de-fragmentation programs, file compressors (zip files), repair to corrupted files.

The screenshot shows a file management program in action:

De-fragmentation is important to do from time to time.  When files are updated the next bit of the file is NOT crammed in with the rest of the file, it is placed in the next free space.  Look at the diagram below:

The first file then gets up dated.

The free space gets filled.  Now we up date the next file:

and the next..

Then we do a lot of work on the first file to get:

You can see that the file is starting to get broken up and ends up in several pieces.  The computer keeps a record of where everything is kept in the registry.  However if a file is fragmented, it will take longer to load because the computer has to look for each piece.  Eventually the computer will be noticeably slow.  De-fragmentation will do this:

This will allow files to be read as a whole.  As further work is done, fragments will occur again, so de-fragmentation has to be done on a regular basis. If a computer disk is badly fragmented, the de-fragmentation process may take a long time, possible several hours.

Question 3   Describe three utilities you would normally find with the operating system of a home PC.  State a typical task for which each utility is used. ANSWER

Other Systems Software

• Systems software is the name given to the range of programs that are used to manage the computer, including the operating system and utilities, both of which we have considered.  There is a further range of systems software:

• Programming language compilers to translate the program statements of C, Pascal, Visual Basic, and other programs into machine code, the instructions that the computer understands.

• Performance monitoring software, which allows the computer managers to check on the optimum performance of the computer.  This is especially useful with a mainframe. The picture shows performance monitoring software on a PC.

• Communications software is used with remote terminals passing data to a mainframe and controls the flow of data to and from remote locations.
• Virus checking software which protect the data from the havoc caused by a virus infection.  It can offer the user the choice of repairing the infected file (by cutting out the virus code), or quarantining it (moving it to a special folder), or by deleting it.

Question 4  A virus checker detects a virus.  Write three things the virus checker may do with the infected file. ANSWER

Now go on to Applications Software