How do magnetic, optical and solid-state storage work, and how do RAM, ROM and virtual memory fit together?
Input, output and storage devices: how different input and output devices are used, the characteristics, uses and operation of magnetic, optical and solid-state (flash) storage, the difference between RAM and ROM, and virtual storage.
An OCR H446 answer on input, output and storage devices: how input and output devices are chosen for a task, the operation, characteristics and uses of magnetic, optical and solid-state storage, the difference between RAM and ROM, and what virtual storage means.
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What this dot point is asking
OCR wants you to choose appropriate input and output devices for a scenario, and to describe how magnetic, optical and solid-state storage physically work along with their characteristics and uses. You must also distinguish RAM from ROM and explain virtual storage. Expect comparison ("compare", "discuss") questions tied to a real situation.
The answer
Input and output devices
Three storage technologies
RAM, ROM and virtual storage
Examples in context
A games console pairs a fast SSD (quick loading) with optical or downloaded distribution. Data centres use tape libraries for cold archives because the cost per terabyte is unbeatable. Smartphones rely entirely on solid-state flash because it is small, shock-resistant and low-power. Virtual memory is why a machine with 8 GB of RAM can still open more applications than fit, by paging the least-used data out to disk, at the cost of slowdown ("disk thrashing") if overused.
Try this
Q1. State one characteristic that makes solid-state storage more suitable than a hard disk drive for a laptop. [1 mark]
- Cue. No moving parts, so it is faster, more shock-resistant, silent and lower-power (any one).
Q2. Explain why ROM rather than RAM is used to store the bootstrap. [2 marks]
- Cue. The bootstrap must be present the instant power is applied; ROM is non-volatile and keeps its contents without power, whereas RAM is volatile and would be empty at switch-on.
Q3. State what virtual storage allows a computer to do. [1 mark]
- Cue. Run programs needing more memory than the physical RAM, by using secondary storage as if it were extra main memory.
Exam-style practice questions
Practice questions written in the style of OCR exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
OCR 20196 marksA photographer needs portable storage for large image files that will be carried into rough field conditions. Compare a magnetic hard disk drive and a solid-state drive for this purpose.Show worked answer →
Reward a developed comparison reaching a conclusion (levels of response).
A magnetic HDD stores data as magnetised regions on spinning platters read by a moving head; it offers a high capacity per pound but contains moving parts, so it is heavier, slower to access (rotational and seek latency), uses more power and is vulnerable to shock damage if dropped.
An SSD stores data in non-volatile flash memory cells with no moving parts, giving much faster access, lower power, silent operation, less weight and far greater resistance to physical shock; its drawback is higher cost per gigabyte and a finite number of write cycles.
For rough field conditions and portability, the SSD's shock resistance, speed and low weight outweigh its cost, so it is the better choice. Top marks require the shock and portability points linked explicitly to the field-work scenario.
OCR 20214 marksExplain the difference between RAM and ROM, and give one typical use of each in a computer system.Show worked answer →
RAM (2 marks): Random Access Memory is volatile (loses its contents when power is removed) and read/write; it holds the operating system, programs and data currently in use so the processor can access them quickly. Use: holding the running OS and open applications.
ROM (2 marks): Read Only Memory is non-volatile (keeps its contents without power) and normally read-only; it holds firmware that must survive a power-off. Use: storing the bootstrap / BIOS that starts the computer when it is switched on. Markers reward the volatile vs non-volatile contrast plus one valid use of each.
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