Hardware, Operating Systems and Architecture

The computer under the case

Every computer, from a phone to a games console, is built from the same few kinds of part working together, and this module is about what they are and what each one does. At the centre is the CPU, the processor that actually carries out instructions. It works through the fetch-decode-execute cycle: it fetches the next instruction from memory, decodes what it means, executes it, and repeats, billions of times a second. Around it sits memory. RAM holds the programs and data in use right now but forgets everything when the power goes off. ROM keeps the small set of startup instructions even with no power. Longer-term files live in secondary storage. Over all of it runs the operating system, which manages the hardware so your programs do not have to. This module covers each of these and how they fit together.

Words for the hardware

Learn what each of these means before you use it.

RAM against ROM

The two kinds of main memory are easy to confuse, so it helps to set them side by side.

How to answer a hardware question

Hardware questions reward precision, so use a simple routine. First, name the exact component the question is about, the CPU, RAM, ROM, a type of secondary storage, or the operating system. Second, state its one main job in a single clear sentence. Third, if the question asks you to choose or compare, give the reason: speed, whether it keeps data without power, or cost. A weak answer says a computer just has memory. A strong answer names which memory, says exactly what it does, and gives the property that decides the choice. Name the component, state its job, give the deciding property.

Match the component to its job

Which memory?

A computer needs to store the small set of instructions that let it start up, and these must still be there after the power has been off all night. Which type of memory holds them?

• ROM
• RAM
• the CPU
• the monitor

Order the fetch-decode-execute cycle

Put the steps the CPU repeats to run a program in the correct order.

• Fetch the next instruction from memory
• Decode the instruction to work out what it means
• Execute the instruction
• Move on and repeat the cycle for the next instruction

Spot the true hardware facts

Tap the TWO statements that are true.

• RAM is volatile, so it loses its contents when the power is off
• Solid-state storage has no moving parts
• ROM is where all your documents and photos are normally saved
• The main job of the CPU is to store files for the long term

Count the cycle stages

The fetch-decode-execute cycle has 3 stages. You have just named the fetch stage, which is 1 of them. Subtract to find how many stages of the cycle are left to name.

Complete the hardware facts

The processor that carries out a programs instructions is the _____. Memory that is lost when the power is switched off is described as _____. Storage with no moving parts, which is fast and hard wearing, is _____ storage. The software that manages the hardware and the running programs is the _____ system.

Choosing the right storage

Imagine picking the storage for a light, portable laptop that gets carried around all day. Think it through by properties rather than by habit. A drive with spinning magnetic platters holds a lot for a low price, but it is heavier, uses more power and can be damaged if it is knocked while running. A drive with no moving parts is lighter, starts programs faster and survives being jolted, though it costs more for the same amount of room. For a laptop that is moved about constantly, the jolt-proof, fast, low-power option is the better fit, and you would justify it in exactly those words. The lesson is that there is no single best storage: you match the properties of the storage to what the device actually needs.

Build the memory rule

Choose the words that complete the rule about the two kinds of main memory.

Pick the hardware

Read each case and choose the best answer, then think about why.

• A user complains that their computer slows down badly when they open many programs at once. Which upgrade most directly helps?
• A washing machine contains a small computer that only ever controls its wash programs. What is this an example of?
• You must recommend storage for a rugged camera used on expeditions where it is often knocked. Which fits best?

Hardware and the operating system

Select the TWO statements that are true.

• The operating system manages memory, files and running programs
• The CPU runs programs through the fetch-decode-execute cycle
• ROM is where a user normally saves their documents
• RAM keeps its contents safely when the power is turned off

Explain the hardware

A friend is revising Computer Science and does not understand what the main parts of a computer do. Explain how the hardware works together to run a program.

• Explain what the CPU does and name the stages of the fetch-decode-execute cycle
• Explain the difference between RAM and ROM, including volatile and non-volatile
• Explain what secondary storage is for and give one property that decides which type to choose
• Explain what the operating system does
• Finish by explaining what an embedded system is, with an example