Show understanding of methods of file access

What is File Organisation?

Think of a file as a big library. File organisation decides how books (records) are arranged on the shelves.

• Contiguous – all books in one long shelf.
• Linked – each book points to the next one.
• Indexed – a small index book tells you where each book is.
• Hashed – a key (like a locker number) instantly tells you the shelf.

File Access Methods

How you read or write to a file depends on its organisation.

1. Sequential Access – read one book after another, like flipping through a magazine. Best for reading the whole file.
2. Random Access – jump straight to a specific book using its address. Like using a library card catalogue.
3. Indexed Access – use an index to find the book quickly. Think of a phone book lookup.
4. Hashed Access – use a hash function (like a locker number) to locate the book instantly.

Time Complexity Cheat‑Sheet

Exam Tip: Choosing the Right Access Method

When answering questions:

• Identify the file organisation first.
• Match it to the most efficient access method.
• Use the time‑complexity table to justify your choice.
• Remember: Sequential is great for reading all records, Random for updating a single record, Indexed for searching by key, and Hashed for constant‑time lookup.

🧩 Practice: Sketch a small file (5 records) and label which access method would be fastest for each operation.

Quick Quiz

Which file organisation would you use if you need to update a single record many times?

1. Contiguous
2. Linked
3. Indexed
4. Hashed

Answer: Hashed – because it gives you $O(1)$ access to the record you want to change.