External hardware devices study guide

A. Build a complete device explanation

For each of the barcode reader, digital camera, laser printer and RFID, prepare an answer under four headings: purpose, main characteristics, principle of operation and suitability. The purpose should state what role the device has in a computer system. The characteristics should be linked to that role. The principle of operation should explain how the device performs its input or output function at an appropriate level. Suitability should be justified in relation to the application named in the question.

A useful structure is: “This device is suitable because its characteristics support the required purpose. It operates by providing or producing the relevant form of data or output.” Do not stop at “it is suitable”; identify the characteristic and connect it to the application.

B. Explain the need for secondary storage

Begin by distinguishing secondary storage from the general working needs of a computer system. The key question is why a computer system needs a secondary-storage device. Then identify the device being discussed and explain its characteristics, purpose and principle of operation. The specification requires hard disk, optical disk and SSD to be considered, so revision should cover all three rather than concentrating only on SSDs.

C. Compare capacity and speed of access

When a question asks which medium is suitable, make two explicit comparisons:

1. Capacity: consider whether the medium can provide the storage capacity required by the application.
2. Speed of access: consider how quickly the application needs data to be accessed or transferred.

Finish with a judgement. For example, an answer can state that one medium is more suitable because its capacity or speed better matches the requirements, while acknowledging the other factor where relevant. Avoid claiming that one device is best in every situation; suitability depends on the application described by the question.

D. Work through SSD writing carefully

A strong SSD explanation should follow this sequence:

1. An SSD uses NAND flash memory.
2. Its storage is based on floating-gate transistors that trap and store charge.
3. A controller manages pages, blocks and the complexities of writing.
4. A block contains many pages.
5. A page cannot be overwritten directly; it has to be erased before it can be written to.
6. The technology requires the whole block to be erased.
7. Therefore, changing information associated with a page involves a restriction at block level, which is a key part of the SSD writing mechanism.
8. SSDs have lower latency and faster transfer speeds than magnetic disk drives, so speed of access and transfer should be considered in an application judgement.

E. Self-check questions

• Can you classify each named external device as input or output where appropriate and explain its purpose?
• Can you give a characteristic and link it to suitability rather than merely listing a feature?
• Can you explain why secondary storage is needed within a computer system?
• Can you describe the relationship between an SSD's floating-gate transistors, NAND flash memory, pages, blocks and controller?
• Can you explain why a page cannot simply be overwritten?
• Can you compare capacity and speed of access and reach a justified suitability judgement?

If an answer misses the mechanism, the comparison or the final judgement, it is incomplete even if the device names are correct.