A chemical plant has a reaction vessel where the temperature is critical to the result of the process. The temperature is monitored by a computer which accepts input from a sensor and then makes a decision whether to adjust the heating elements in the vessel. In this example, it would not be sensible for the computer to be running any O.S. that is not real-time because if there was a delay in the decision making process, it might mean that the reaction is corrupted in some way.
A robot trolley is controlled by a processor which takes input from a sensor following a black line on the floor, and makes decisions concerning steering to keep the trolley on the black line. If the processor was not controlled by a real-time O.S., the trolley would very soon leave the black line because it would not be steering quickly enough.
A catalogue shop processes orders by the code for a product being input and the system then comparing the code with information in its files. When it finds the correct code it can report to the user the number of that item that there are in the store. If there was only one left of a certain item, it would be necessary to record the fact that a shopper had bought it before the next shopper has their request dealt with otherwise the second person might be sold the same item.
Because the information on the system must be processed immediately the O.S. needs to be ready to handle input as soon as it comes in. This means that it cannot be using up some of its slack time doing other tasks while it is waiting to be asked to do something. This implies that the computer will not be using its full potential as far as processing is concerned. When this happens it is said to display a high rate of redundancy. Real-time systems tend to display a high rate of redundancy. Real time is the most important thing. Making sure that the CPU is used as efficiently as possible as with batch processing is not important.
As the term implies, a single user O.S. is specifically one that is used to control a system, which has only one user, and their programs, at any one time. A perfect example of a single user system is the one that you may have at home. Only one person uses it at a time. Most single user systems are also
Multi-programming:
This is a type of O.S. that allows several applications to be available simultaneously. On a simple single user system the user will probably be used to having a number of things running at the same time. Perhaps one window shows a spreadsheet while another shows a word processing application. The user may decide to copy the sheet from the spreadsheet software to the word-processed document. It appears that more than one task is running simultaneously. They aren’t, they just appear to be. The O.S. that most of us use on our own computer systems, Windows, is a multi-programming O.S.
A multi-access (multi-user) operating system is defined as one that allows two or more users to communicate with the computer at any one time, with each user interacting with the computer via a terminal (which must have, at the minimum, a keyboard and VDU). This is achieved by sharing the computer’s processor, main memory and file store. Each application program resident in main memory is executed a bit at a time by rotating the use of the processor between them. The trick of giving a user the impression of having sole access is achieved by choosing, for each turn, the right length of processor time. Too long and some users will notice delays. Too short and all users will find that processing is noticeably slowed.
There are two types of multi-user Operating systems:
- A network system comprises a number of computers linked together for the purposes of communication and sharing of resources. Normally one of the machines is used to control the rest of the system, this machine is called the server.
A Network Operating System (NOS) is an operating system that gives computers the ability to communicate with other computers on a network. NOS software often includes extra facilities to allow back-ups and improve security, for example. Some widely used NOS software includes Novel and UNIX.
This is a piece of software that 'manages' a network. A Network Operating System typically:
controls communication between workstations themselves and between workstations and servers.
allows and manages file sharing
allows and manages printing and other resources.
controls Internet access amongst stations
manages user accounts
manages security
manages automated system back-ups
manages and reports on the use of the system's resources, such as each user's hard disk allocation and how many prints they are allowed to do.
provides a number of different user interfaces. This allows different categories of user to access the network, for example, an interface to allow the network administrator to set up account, an interface to allow the personnel manager to access employee details or an interface to allow secretaries to access generic applications.
2. A time-sharing system has a single (normally powerful) computer which is connected up to a number of terminals. These terminals are not computers as in the case of the network system, but have a very limited amount of processing power. Again, such a system allows communication between users on the system and also allows sharing of hardware and software across the system.
A distributed system is one that allows software and data files to be distributed around a system. An ordinary network will have a server controlling it and the access to the hard drive, which is connected to the server. A distributed system might store the word processing software on one computer’s hard drive, while the files of work are stored somewhere else, and the spreadsheet software is stored on a third disk drive. This can speed access to files because there is no single bottle neck which all the information must pass through.
User Categories
Categorisation of users is very important for an interface designer and users have been categorised by many researchers on some basis. The broad sub-division of users and their characteristics are
Naive:
Users who have not encountered computer systems. They may show fear of using computers, will be unfamiliar with the working of the system and may not have knowledge of how to operate it. These types of users are becoming very rare because of rapid computerisation.
Novice:
These users have some experience of working with computers, but may be unfamiliar with a new system. They are liable to make mistakes because of their limited experience. Most of the users of a new system will start as a novice.
Skilled:
Users who have considerable expertise using the system. Most of the users become skilled due to frequency of use. They will be able to operate the system efficiently, but will have limited knowledge or no knowledge about the structure of the system. They will not be able to solve unexpected errors.
Expert:
Users who have thorough knowledge about the working of the system and their internal structure. They will have the ability to maintain and modify the basic system.
Types of User Interface
Communication between a user and a computer is two-way. A user will give data and instructions to a computer and a computer will give information back to a user. The may that a computer and a user communicate is known as the ‘interface’. Another common term is Human-Computer Interface or HCI. There are different types of interface, which are useful in different situations and for different types of user.
If the majority of the input to a system is of a standard type, in other words the computer knows what sort of input to expect, then a typical interface will produce a form on the screen to be filled in. This sort of interface would be used where an operator is inputting information while asking a customer questions over the telephone. The interface
- prompts the operator to ask all the questions
- makes the operator input the information in the correct order
- ensures that the information is input in the correct format by having specific areas to input the data
- makes the checking of the information easier.
The characteristics of a form based interface are that
- There are field names, names next to a place where information must be entered
- There are places called ‘response fields’ where information is entered by the user.
- The cursor ‘tabs’ automatically from one response field to the next. This guides the user logically through the form, ensuring that all the information is gathered.
- As data is entered, it is ‘validated’. Validation attempts to ensure that only sensible data is entered into the system and data that is not sensible is rejected. Validation helps ensure that data entered into any system maintains its ‘integrity’.
- Input can be changed/ cancelled if necessary.
- Data is finally entered into the system only when an‘OK’ button, ENTER or something similar is pressed.
Form-based interfaces are very suitable for any application that involves entering predictable pieces of information into the computer. For example, someone taking a telephone order for a product, someone recording responses to questions in a telephone questionnaire and someone entering in details of a person who wants to apply for a credit card might all be done with the aid of a form-based interface.
Menu-based systems are ideal for situations where the user’s IT skills cannot be guaranteed or in situations which require selections to be made from a very wide range of options or in situations which require very fast selection.
The user of a system that uses a menu-based interface will be presented with a limited number of options on the screen. Once a selection has been made, the user is presented with a sub-menu. This gives them further options. They make another selection and may be presented with a further sub-menu. This continues until the user is able to select exactly what they want from the choices finally displayed on the screen.
Menu-based systems are ideal for large information systems. Using a system of selecting from menus and sub-menus, the required information can quickly be found.
Imagine a computer system at a tourist information center that has got a menu-based interface. A tourist, who may not have any IT skills, could be presented with a screen with 10 buttons on it, perhaps listing theatres, cinemas, parks and libraries, for example. They could touch the touch screen to make a selection of the general area of interest. If they selected ‘Cinemas’, for example, they might then be given details of the closest cinemas in the area. If they select one of these, they could then be presented with the films that are currently showing.
Consider a factory where workers are working in a noisy, dirty environment. Workers may not want to be fiddling around with keyboards, typing in commands. They could have a menu-based interface instead. This will quickly allow them to find the option they want and to select it simply by touching a touch screen.
Consider a stockbroker. Their job may involve sitting at a computer screen and watching how many different share prices are changing. Shares may be grouped and they can select a particular group or an individual share quickly by selecting a type of share from a menu. They might then select a subset of that type from a sub-menu and so on, until they get the group of shares or the individual share they want to monitor. It is far quicker to find what they want using menus and sub-menus than it is typing in commands.
Interfaces that are graphical in nature are known either as Graphical User Interfaces(GUI) or WIMP interfaces (Windows, Icons, Menus and Pointer). Typically, these types of interfaces are available in multi-programming environments or in applications software that involve a considerable degree of complexity.
In a GUI, there are:
- A ‘window’ for each open application. Many windows can be open at the same time but only one window can be active at any one time. There may be some way of indicating which one is active (perhaps by making the bar at the top of the active window blue)
- Menus and icons. Available functions can be selected in one of two ways, either by using pop-up menus or drop-down menus, or clicking on ‘icons’. An icon is simply a small picture that represents a specific function- clicking on it selects that function.
- A pointing device, usually a mouse but in certain circumstances a graphical tablet and pen can be used. These are used to make selections.
- The use of the keyboard to navigate through the application is minimized because it is relatively time-consuming way of working.
Natural language interfaces are those that allow the user to communicate in their native language, such as English. It allows the user to instruct the computer without need for a particular 'syntax'. The system needs to be able both to interpret inputs in natural language from the user, and to act upon them, and, also preferably to generate natural language statements in response to user input. Sometimes it is also referred as a conversational interface.
The questions are displayed on the VDU and the answers are entered via the keyboard. For example, imagine a user has initiated a ‘save file’ request. The ‘conversation’ might be:
COMP:What’s the file name?
USER: chapter1.txt
COMP:what folder?
USER: userguide
COMP:File already exists.Overwrite?
USER:Yes
COMP: Done.
This kind of interface can be found on data entry terminals and other types of dumb terminals connected to a network where non-experts users are guided through the complex tasks they need to perform by the computer.
Command based interface is one where the user types a series of commands at the keyboard which tell the computer what their intentions are. It is also known as linguistic manipulation. The characteristics of a command based interface are
- the user needs to know what commands are available
- the user needs to understand the commands
Characteristics of a command based interface
- The system is very much more open than in the other types of interface. Other interfaces restrict the options that the user has available to them. This can be particularly important for the system manager because different users can only be allowed to have access to specific parts of the system.
- Command based interfaces can only be used by computer literate people because the user need to understand the commands and their uses.
1. Define what is meant by the term operating system. (2)
2. Give two reasons why an operating system is likely to be stored on backing storage rather than in the memory of the computer. (2)
3. Distinguish between a multi-programming and a multi-access operating system. (2)
4. State what is meant by a distributed system, and give an advantage of this type of multi-access system over a simple network of machines.(2)
5. A computer operator takes phone calls from the public who ring up asking whether a particular item in a catalogue is available. The operator needs to type in a series of responses to questions put to the caller, so that the computer can check the file and determine whether there are any of that item available. Design a screen interface that would be suitable for the operator to use. (4)
6. The technician responsible for maintaining the system in question 5, uses a command line interface.
a) Explain what is meant by a command line interface. (2)
b) Give two advantages and one disadvantage to the technician of using a command line interface rather than a menu based interface. (3)
Answers:
1 A. -A (suite of) programs…
-which run the basic functions of the computer…
-giving an environment in which to run application software.
A question which begins with the word define, leaves very little room for manoeuvre because it is asking for a standard answer. This is not an opportunity to show your prowess by making up an answer that is original- there aren’t any. Note, also, the fact that three answers have been given. Always try to give one more answer than seems to be required by the question.
If you look at a mark scheme for an examination paper, the mark points are listed as a set of bullet points so there is no reason why you should not do the same. This style of answer helps you to write down your thoughts easily without getting confused by the language. The purpose of this examination is not to test your ability with English, rather to test your knowledge of computing.
2 A. - A full operating system requires a large amount of storage space that is better utilised in the computer memory for applications
- Storage of the operating system on backing storage allows for easy upgrading or changing from one system to a different one.
Note that the temptation to call the operating system the O.S. has been resisted in the answer. In general, do not use abbreviations in your answers. There are exceptions, where the abbreviation is the accepted form, but your own versions may be ambiguous or, even, not understood by the examiner. If you do need to use an abbreviation, because the term is to be used a number of times, give the term in full with the abbreviation that you want to use in brackets after it. For example, the first time that you use the term operating system write “…operating system (OS)…” you can then use OS as often as you like in the rest of your answer.
3. A. - A multi-programming operating system is one where the user of the machine is given the impression that they can carry out more than one task at a time.
- A multi-access operating system is one where it is possible for more than one user to access the system apparently at the same time.
Note that there are a large number of points that could have been made about both of these operating systems, but most of them would not answer the question. It is important when answering a question starting with ‘distinguish’ to choose facts that show a comparison.
4 A. - A distributed system is one which uses many storage locations on different machines to store software and files.
- Access to files can be speeded up because more than one file command can be carried out at a time.
When an advantage is asked for it is normal to state in the question, either explicitly or implicitly, with what the comparison should be made. Be careful to give an advantage using this comparison and not a more generalised one.
5 A. - Form type interface
- Catalogue number
- Space for the description of goods which will be filled in by the computer itself
- Spaces for computer to produce availability and price
- Laid out with spaces for input.
What is just as important here are the things that would not be on the screen. The question makes it quite clear that there is no ordering going on, so spaces for name and address, or method of payment, are not only going to score no marks, but will probably be penalised because they demonstrate that the candidate has not understood the question. In this type of question it is important to demonstrate that you have taken the situation into account.
6 A. a)-Series of commands typed at a screen prompt…
-which give specific instructions to the computer.
b)Advantages:
-Entire system is available to the technician
-Access to the particular part of the system required is gained more quickly than using other types of interface.
Disadvantage:
-The technician needs to know the commands that are available
-The technician needs to understand the way the system is designed so that it can be navigated efficiently.
Note. The language used in this answer is not the sort of language that a candidate will use in an examination. Don’t worry about this. Answers like “so that you can get around the system” are perfectly acceptable.
