The ICT Lounge
 
Section 3.2:
Ways in which Data is Stored and Read
 
In this section we will look at the 2 main ways in which data is accessed, stored and read:
  • Serial Access (also known as 'sequential access)
  • Direct Access (also known as 'random access)
Use the information provided to fill out the research sheet which can be downloaded from the bottom of this page.
Key Concepts of this section:
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Know the difference between 'Serial' and 'Direct' data access.
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Understand how both serial and direct access work.
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Be able to state the different uses of serial and direct data access storage methods.

Serial Access
Key Words:
Serial, Sequential, Sequence, Magnetic Tape
Overview:
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This method is also sometimes called 'Sequential Access'.

Examples:
Serial data access reads data in 'sequence'.
 
Old film reels access the movie's scenes in 'sequence'. E.g. from start to finish.
 
Magnetic tape can store a lot of data but it
is slow to access it.

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Data is accessed by starting at the beginning and then searched through, in order/sequence, until the required information is found.

Kind of like an old film reel where the movie starts at the beginning and data is read
in order until the movie is finished

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The need to search from the beginning of the storage medium makes this type of data access very slow.


Where Serial Access is used:
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Serial access is used on old magnetic tapes.

These are used where it is necessary to store a lot of data but where speed of access is unimportant.

Magnetic Tapes are still used for backing up large amounts of data in organisations like schools and business.

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Serial access medium (like magnetic tapes) are also used in batch processing systems like payroll and in the preparation of utility bills.

The way that serial access works means that all of the data has to be read and there is no danger of missing out someone's wage payment or bill invoice.

Remember:
Serial access works by accessing the data at the beginning and then working through it bit-by-bit until the end.

This is why there is no danger of missing anything out during the batch processing examples above.

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Examples of storage medium that use serial access are:
  • Video cassettes
  • Music cassettes
  • Backup tape cartridges (hold lots of tape for backing up large amounts of data).

Direct Access
Key Words:
Direct, Random

Overview:
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This method is also sometimes called 'Random Access'.

Examples:
Direct access can go straight to the required
data 'directly'.
 
DVD movies allow you to jump to scenes. This is possible through direct access.
Flash memory cards are an example of storage medium that use direct access.
 
CD-ROMs and memory sticks also use direct access.

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The computer can calculate exactly where the data has been stored and can go straight to it directly (instant access).

The computer knows where all of the data on the storage medium is and so it can
access it very quickly.  

It is not forced to start accessing the data at the beginning and then working through
bit-by-bit like with serial access.

A good comparison as to how direct access differs to serial access is to think of how
DVD movies work compared to old film-reel movies.

In a DVD movie you can 'jump' directly to any scene you want but in a film-reel you
have to move through every scene until you come to one you want.

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This 'direct' method of accessing data is much faster than serial access.


Where Direct Access is used:
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This method is used with storage medium such as:
  • Hard Disk Drives
  • CD's and DVD's
Direct access is used on most modern storage devices where speed of access is important.

Note: The large size of modern files makes direct access even more useful.
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Direct access medium are used in situations where fast access to data is important like in online booking systems and point-of-sale (POS) terminals in shops.

For example:
You wouldn't want to wait around at a shop checkout while the system was trying to access the price of beans!

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Other examples of storage medium that use direct access are:
  • USB memory sticks
  • Flash memory (like in digital cameras and mobile phones)
  • Blu-ray discs

Activity!

Click the above task and write-up the required information about the different ways that data can be accessed.

Links to Theory Units:
Section 4: Networks and the Effects of using them
Section 6: ICT Applications
Section 7: The Systems Life Cycle
Section 8: Safety and Security
Section 9: Audience
Section 10: Communication
 
Links to Practical Units:
Section 11: File Management
Section 12: Images
Section 13: layout
Section 14: Styles
Section 15: Proofing
Section 16: Graphs and Charts
Section 17: Document Production
Section 18: Data Manipulation
Section 19: Presentations
Section 20: Data Analysis
Section 21: Website Authoring