F. Filing Systems

What is a filing system?

Virtually every computer application (barring the most trivial) requires some

kind of access to an external storage medium, for example a magnetic disc, with

which to save information. There are several possible reasons for this, the most

common one being that the contents of the computer's memory is not

maintained when you turn off the power. Also, it is quite usual for programs to

need to work with more data than can be accommodated in the main memory of

the computer along with the program itself. Clearly, if programs and data are

to be stored outside the memory in this way, the user must be provided with a

convenient means of referring to them, in order to:

-- retrieve (LOAD) existing items;

-- access existing items selectively (i.e. without having to load them in their

entirety );

-- store (SAVE) new items.

The items are normally referred to as files because of their similarity to the

cardboard files offices use to store information tidily. A filing system provides

a convenient way of performing these tasks, along with a variety of other

'housekeeping' facilities.

Standard Filing Systems

Your computer comes equipped with two standard filing systems:

-- the ROM Filing System (RFS)

-- the Advanced Disc Filing System (ADFS)

thus enabling the computer to access files held on Read-only Memory (ROM)

chips and on conventional flexible ('floppy') magnetic discs. Additionally,

further optional filing systems can be added to the computer enabling it, for

example, to act as a workstation on an Econet network.

Whenever the computer is switched on, or subjected to a 'hard' break

( + ), it automatically selects the filing system which has been

designated by the contents of the configuration memory (see page B l0). This

becomes the current filing system and remains in force until you instruct the

MOS that you wish to use a different system (using commands described

below).

It is worth noting that each filing system is, as far as possible, compatible with

the others. This means that the command required to, say, load a file into

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