Comparisons
Advantages of teletext compared with viewdata
1 It is relatively easy to select the information you want.
2 The equipment required is fairly inexpensive.
3 No money is needed to use the system once you have the equipment.
4 Teletext data can be added to ordinary television pictures. For instance deaf people can have subtitles added to television programmes by this method.
5 Pages can be changed easily so that information is up to date.
Disadvantages of teletext
1 Only a limited number of pages can be looked at.
2 There is no interaction with the computer.
Advantages of viewdata
1 A wide variety of interactive services. They range from electronic mail to travel information and facilities for ordering goods.
2 The amount of information available is very large.
Disadvantages of viewdata
1 On some systems response is slow and the method of searching is cumbersome.
2 Cost of telephone calls and of charges for using the system.
Viewdata in Britain has not increased as much as was expected originally. There are still only about 60000 Prestel subscribers. This compares with over 3 million users of the corresponding French system, which has started much more recently. This is partly because the French system is heavily subsidized.
Advantages of electronic mail over post
1 Less use of paper. It is possible to read and reply to correspondence without it being printed out. A letter can be written using a word processor and transmitted direct.
2 Speed. A message transmitted to a user’s mailbox can be read almost immediately.
3 Simplicity. If an employee of one company sends a letter by post to an employee of another. a chain of people is involved. Electronic mail only involves the computer system and the two people concerned.
Disadvantages of electronic mail
1 Electronic mail can only be sent to people who subscribe to the service.
2 A user does not know any mail is in the mailbox until he or she logs on to the system.
3 It is expensive to use a public network .
Note: These first three disadvantages are not significant for subscribers who use an electronic mail system regularly.
4 Widespread use of electronic mail would be worrying for postal and office workers as their jobs could be endangered.