13.2 File organisation and access

2026 Syllabus Objectives

By the end of this subtopic, you should be able to:

  • show understanding of the methods of file organisation
  • choose a suitable method of file organisation and file access for a given problem
  • understand serial, sequential using a key field, and random using a record key
  • understand methods of file access
  • understand sequential access for serial and sequential files
  • understand direct access for sequential and random files
  • understand hashing algorithms
  • describe and use different hashing algorithms to read from and write data to a random or sequential file

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What file organisation means

A file stores data on secondary storage. The data inside a file is usually stored as records. A record is one complete set of related data about one thing. For example, one student record might contain a candidate number, name, and mark.

When we talk about file organisation, we mean the way those records are arranged inside the file.

This matters because the arrangement affects:

  • how easy it is to add a new record
  • how fast it is to find a record
  • how easy it is to update or delete a record
  • which access method is most suitable

So, file organisation is really about one big question:

How should records be stored so that the file works well for its job?

In this topic, you need to know three file organisation methods:

  • serial
  • sequential
  • random

You also need to know two file access methods:

  • sequential access
  • direct access

It is important not to mix these up.

  • File organisation = how the records are stored
  • File access = how the records are found

1. Serial file organisation

In a serial file, records are stored one after another in the order they are added.

That means the first record entered goes first, the next one goes after it, and so on. New records are usually appended to the end of the file.

So a serial file is based on time of entry, not on sorting by any field.

Main features of serial files

A serial file:

  • stores records in the order they arrive
  • does not need a key field to decide where records go
  • is easy to add to, because new records are just placed at the end
  • is often used when data is collected over time

If hourly temperature readings are stored as they are recorded, the readings naturally arrive in time order. A serial file is a good choice because each new reading can simply be added to the end.

Why serial files are useful

Serial files are useful when:

  • records are created continuously
  • the order of arrival matters
  • it is more important to add records quickly than to search quickly

A good example is a transaction log. Every new transaction can be added to the end as it happens.

Limits of serial files

The disadvantage is that finding one specific record can be slow. Because records are not arranged by key value, the file often has to be searched from the beginning until the record is found or the end is reached.

So serial files are simple, but not the best choice when very fast searching for one record is needed.

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