Introduction to information systems T. Cornford, M. Shaikh is1 060 2013

Figure 4.1: A QR code for the website www.londoninternational.ac.uk
4.4.2 Data storage devices
Reading activity
Read Chapters 3 and 8 of Curtis and Cobham (2008). Read Chapter 6 of Laudon and 
Laudon (2013).
Main memory is volatile, but data (including software) needs to be stored 
permanently, securely and economically. Computers therefore have forms 
of non-volatile storage, referred to as secondary storage or backing store. 
Files and file processing
Magnetic discs, and − to a lesser degree − magnetic tapes, have historically 
provided the basic storage capability for computer systems. The way in 
which data is organised and accessed using such devices is the topic of files 
and databases. A file is a named unit of data stored within a computer. For 
example, the word-processed version of this document is stored in a file. 
It is held as a sequence of characters and control codes. The organisation 
is vital – the characters must be retrieved in the same sequence they were 
stored; otherwise the document would be unreadable! For data-processing 
applications, we often think of files slightly differently – as structured in 
terms of records made up of fields. For example, one record per customer, 
with fields for name, address, phone number, etc.
Transaction processing applications (the back-office computing) may often 
revolve around a master file that maintains the essential data and which 
is updated by various types of transaction. These transactions may be 
stored in a transaction file. 
For purposes of security and integrity, copies should be made of data 
stored on computers; hence another type of file is a back-up file. 
Reminder: do remember to back up your project files. You 
are responsible for managing this data and keeping safety 
backups.

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Chapter 4: Contemporary trends in information and communication technologies
57
Example
The customer accounts system of Multinational Bank has a file of customer 
account details – a sequence of records, each containing data on individual 
customers. Among the fields that occur within each record are:
• name
• customer number
• date of first opening an account
• address
• telephone number
• email address. 
The file is used whenever a person is contacted in any way. In practice, these 
records will need to be accessed in any order, depending on which customer a 
bank employee wishes to contact (called random access). The customer number 
field has a special status as the key field, because the customer number allows 
the correct record to be uniquely identified and retrieved. Note that the bank 
has 25 customers called John Smith! And most of these have more than one 
account at the bank. The file is stored on disc, and we can go directly to read 
any record if we know where on the disc it is stored. In practice we would 
expect some database management software to take care of most of the detail 
of storage and retrieval of these records.
Before the creation of database software − and cheap computer power 
− organising files was an important technical issue. Today, with database 
software in common use, and with cheap computing power and fast storage 
devices of vast capacity, we seldom need to think in such technical detail about 
how exactly data is stored, accessed and retrieved for any given application. 
However, as you will see in undertaking your database assignment, designing 
databases is itself a task that needs to be carefully approached (see Chapter 8 of 
this subject guide).