Storage Showdown

No winner, only trade-offs

You already know the difference between primary and secondary storage: primary is what the processor works with while a program is running, and it is lost when the power goes off, while secondary storage is what survives being switched off - the programs and files still there tomorrow morning. This module is about the three kinds of secondary storage your specification names, and about the only question the exam actually asks of them. Here is what makes this topic different from most. The knowledge is small. There are three technologies, each works in a describable way, and each has strengths and weaknesses you could write out in ten minutes. The knowledge is not what is being assessed. What is assessed is whether you can pick the right one for a particular situation and say why that situation decides it. And that only works if you understand the idea underneath: none of the three is the best. Each is a different trade-off. Magnetic gives you the most storage for your money but has moving parts. Solid-state is fast and survives being carried around but costs more for the same space. Optical is cheap to produce and easy to hand to somebody, but slow and small. So the right answer genuinely changes from question to question, and a student who always writes "solid-state" has not understood what is being asked.

Words for storing it permanently

Six terms. The last two are the ones you will actually be judging with, so learn them as criteria rather than as facts.

Match each type to how it works

What is actually moving

Magnetic storage is generally less durable than solid-state storage. What explains that?

• It has moving parts, so a knock while the disc is spinning can damage it, whereas solid-state has nothing to move
• Magnets nearby will always erase it instantly
• It holds more data, and larger devices are always more fragile
• It is an older technology, so it is worse in every respect

Three technologies, four questions

The four things your specification asks you to judge against. Read down each column and notice that no technology is best on all four, which is the whole point.

Which two suit this job

A company needs to store a very large archive of records in its office, kept for many years and rarely accessed. Select the TWO statements that support choosing magnetic storage here.

• It gives the most capacity for the money, which matters when the archive is very large
• The drive stays in one place, so its vulnerability to being knocked matters much less
• It is the fastest of the three at retrieving data
• It is the most durable option if the device is dropped

Secondary storage in words

Storage that keeps data when the power is off is called _____ storage. _____ storage holds data as patterns on spinning discs and offers the most capacity for the money, but has moving parts. _____ storage holds data electronically with nothing moving, so it is the fastest and the most _____. _____ storage holds data as marks read by a laser, and is cheap per disc and easy to distribute.

Nothing wins on everything

This is the idea the whole topic rests on, and stating it is often worth a mark on its own. There is no best secondary storage. Each technology buys an advantage by giving something up, and which trade is worth making depends entirely on what the device is for. Magnetic buys capacity with fragility and speed. You get far more space for your money, and in exchange you accept moving parts that dislike being knocked and take time to reach the data. Solid-state buys speed and durability with cost. Nothing moves, so it is fast, quiet, light and survives being carried, and you pay more for the same amount of space. Optical buys cheapness and distribution with capacity and speed. A disc costs very little, can be posted or handed over, and can be made read-only so it cannot be altered; in exchange it holds little and reads slowly. ⚠️ So when a question describes a situation, do not ask which technology is best. Ask which of the four criteria the situation makes important, and choose the one that wins on those. A device carried in a bag makes durability and portability decisive. A large archive that stays put makes capacity and cost decisive. Something sent to many people makes cost per copy and ease of distribution decisive. The scenario tells you which criteria matter, and the criteria tell you the answer. That order is the method.

The order to choose in

Put the steps of answering a "which storage would you recommend" question into the order that produces a justified answer.

• Read the scenario for what the device actually has to do
• Decide which of the four criteria that situation makes important
• Choose the technology that wins on those particular criteria
• State the choice, and name the feature of the scenario that decided it
• Concede what the choice gives up, and say why that matters less here

Two jobs, two answers

The clearest way to see why the justification matters is to answer the same kind of question twice and get two different answers. Scenario one: a laptop taken to school every day, used for coursework, needing to start up quickly. The answer is solid-state, and here is the justification: "The laptop is carried daily, so it will be knocked and jolted, and solid-state storage has no moving parts to damage, making it far more durable in that situation. It is also the fastest, which matters because the machine needs to start up quickly. It costs more for the same capacity, but a coursework laptop does not need an enormous amount of space, so that trade is worth making." Scenario two: a video production company storing years of finished footage on-site, accessed occasionally. The answer is magnetic, with a justification that uses the same criteria differently: "Video files are very large, so capacity per pound is the dominant consideration, and magnetic storage provides far more space for the money. The drives stay in the building rather than being carried, so their vulnerability to knocks matters little. They are slower, but the footage is accessed only occasionally, so speed is not a priority here." Look at what the two answers share. Both name the choice, both point at the specific feature of the scenario that decided it, and both concede what the choice gives up and explain why it does not matter in that situation. That last move is the one that separates a justification from a preference. And notice that the same criteria produced opposite answers, which is exactly what a generic pros and cons list can never do.

The generic answer that fits nothing

Four answers recommending storage for a laptop carried to school daily. Select the ONE that gives a generic list rather than justifying against the scenario.

• Solid-state, because the laptop is carried daily and has no moving parts to be damaged by knocks.
• Solid-state is fast, durable and quiet, while magnetic is cheaper but slower and optical holds very little.
• Solid-state, since start-up speed matters here and it is the fastest of the three.
• Solid-state, and although it costs more per gigabyte, a coursework laptop does not need a large capacity.

Say why this one

Assemble a recommendation in the form the mark scheme rewards.

Four situations, four choices

Four different jobs. The right technology is not the same each time, so read what each situation actually needs.

• A museum wants to give visitors a copy of a short film to take home, thousands of copies, cheaply.
• A photographer needs storage in a camera bag, taken outdoors and often knocked about.
• A school needs to back up many years of records on-site, rarely read, on a tight budget.
• You now have to write the justification. What must it contain to earn full marks?

Explain and justify a storage choice

Describe how optical, magnetic and solid-state storage work, and recommend a suitable type for two different scenarios of your own choosing, justifying each against that scenario.

• Explain what secondary storage is and how it differs from primary storage
• Describe how magnetic storage physically works, and what its moving parts mean
• Describe how solid-state storage works and why having no moving parts matters
• Describe how optical storage works and what it is well suited to
• Describe two different scenarios needing storage
• Recommend a type for each, naming the feature of that scenario which decides it
• For each recommendation, say what the choice gives up and why that matters less there
• Finish by explaining why there is no single best secondary storage