     BASIC PRINCIPLES OF DATA STORAGE AND RETRIEVAL ON THE IBM PC

                            Matthew Probert
                           Servile  Software



Data is infomation stored in a computer system. The usual storage 
mediums connected with a personnal computer are disk drives. Disk 
drives may use either fixed or floppy disks. A floppy disk is a small 
easily transportable cartridge which slots into the floppy disk drive. 
The computer is slow to read and write data to and from a floppy disk, 
and the quantity of data which can be stored on a floppy disk is 
fairly small. A fixed disk, also called a hard disk, is a unit built 
in to the computer. The computer can read and write data to and from 
the hard disk very quickly, and the quantity of storage available with 
a hard disk is very large. 

Data can be stored in either an organised, or a disorganised manner. 
An example of a disorganised approach to data storage is word 
processor documents. There may be several documents each recorded in a 
separate file. An organised approach to data storage involves grouping 
data items togther into one file, or into several files but providing 
links between the files. 

Different approaches are suitable for different types of data. It is 
more convenient to store document letters in separate files than in 
one large file. Not because it is easier to locate the required data 
item in this way, but because of the way in which word processors are 
geared towards working with data items having sole use of a file. This 
approach forces the human operator to locate the required data item 
(document) by consulting the names of the files. 

Other data items, such as mailing lists in which each data item is a 
single address, lend themselves to being stored in a single file. This 
is the "flat file" approach. A retrieval system, often called a 
database, can search the file for a supplied data sub-item. A field. 

Applications which involve different classes of data items, such as an 
accounting system, tend to have the data items stored in multiple 
files. Each file storing one class of data. For example one file may 
record customer's names and addresses. Another file records details of 
invoices sent. A further file records details of supplier's names and 
addresses and so on. To help the retrieval system to locate related 
data items, such as a customer's name and address together with their 
invoices, links must be defined between the files. This is the 
relational approach. Retrieval systems for this type of data are 
called "relational databases" or "RDBMS" which is short for 
"Relational DataBase Management Systems". 

In all approaches, a single data item is called a "record". Within 
that data item, structured sub-items such as "name", "address" and 
"Telephone number" are called "fields". A group of records stored 
together are a "file" or "database". 

