课 27, 主题 1

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file-access

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File access methods

What are file access methods?

Once a file is organised and stored, it must be accessed correctly in order to retrieve or update data
The method of access depends on the file organisation used

Sequential access

Sequential access means accessing records one after another, in order, starting from the beginning of the file

Key features	Used with
Reads records in sequence	Serial and Sequential files
Slower for searching large files	Must process earlier records first
Efficient when reading the whole file	Ideal for batch processing (e.g. payroll, reports)

Example: Reading every student’s exam result in order of candidate number

Direct (random) access

Direct access allows a program to jump straight to the location of a specific record, without reading previous ones

Key features	Used with
Accesses records directly by position or key	Sequential (with indexing) and Random files
Fast access to individual records	Ideal for databases and real-time systems
Requires a calculation or index to find the correct location (e.g. hashing)	Useful when you need to look up a record quickly

Example: Accessing a bank account record by account number

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