1.20417 · Section 1: Types and components of computer systems

The main components of computer systems

Key learnings

CPU — fetch, decode, execute
The CPU (central processing unit) processes the instructions entered into the computer in order to produce an output. One cycle repeats: fetch an instruction, decode it, execute it. It fetches programs and data in use from RAM, and start-up instructions from ROM, then passes the result to an output device. A faster CPU — or more RAM holding data ready for processing — completes a task more quickly. "It runs the computer" is too vague to score.
RAM vs ROM — two properties each
Internal memory is the memory the CPU uses directly. RAM is volatile (contents lost when the power is off) and read-write, holding the data and programs currently in use; more RAM chips can be added, letting more programs run at once. ROM is non-volatile and read-only, holding the fixed start-up instructions, and is set by the manufacturer. Answering "memory" for either term earns nothing — give the volatility AND the read/write property.
Input, output and backing storage
An input device sends data into the system to be processed (keyboard, scanner, microphone); an output device presents already-processed data to the user (monitor, printer, speaker). Data direction is the defining difference. Backing (secondary) storage (hard disk, solid-state drive) differs from internal memory by being non-volatile, much larger and slower, so it holds files long-term while RAM holds only what is being processed now.

Common mistakes

Drawn from real examiner reports.

RAM and ROM given the wrong way round

Candidates give the ROM definition when asked for RAM, and the reverse — the most-cited definition trap in this section. Remember the properties, not the letters: RAM is volatile and read-write; ROM is non-volatile and read-only. A definition needs BOTH elements, the volatility and the read/write capability, so "memory" on its own scores zero for either term.

Flagged s23 P11 Q2a; w23 P11 Key Messages — candidates swap the two terms

A blurred A or O costs the mark

RAM and ROM differ by a single letter. Where handwriting blurs the A and the O, the examiner cannot tell which word was meant and no mark can be awarded — raised in Key Messages across sittings, so it is not trivial. Form the two letters distinctly, or write the term out in full (random access memory / read-only memory) if your handwriting is unclear.

Flagged s23 P11 Q2a; w23 P11 Key Messages — careless handwriting made RAM/ROM answers unreadable

"Characteristic" means a property

"State a characteristic" asks for a property, not a description of what the component does and not a named device. For backing storage the credited properties are non-volatile and permanent. "It stores files" or "you save your work on it" describes a use and scores nothing; candidates seemed not to understand the word itself.

Flagged s23 P12 Q12b — the word "characteristic" was misunderstood; correct = non-volatile / permanent

Backing storage is not backup storage

Backing storage does not mean "storage used for making backups". It is secondary storage — any non-volatile storage outside internal memory that holds programs and data long-term, such as a hard disk or a solid-state drive. Candidates who read "backing" as "backup" wrote about copying files for safety, answering a different question entirely.

Flagged s23 P12 Q12b — some thought "backing storage" meant storage used for backups

USB is a port, not a storage device

USB (universal serial bus) is a port — the connection standard — not a storage medium. Asked to name a backing-storage device, candidates repeatedly wrote "USB" and earned nothing. Name the device itself: a memory stick (pen drive) or a portable solid-state drive, which happens to plug into a USB port.

Flagged s23 P12 Q12; w22 P13 Q10 — "USB" repeatedly given as the backing storage itself

A speaker cannot present numbers

Choosing an output device means matching it to the type of data. Numerical and graphical data such as weather readings need a monitor or printer, which the user can read directly; a speaker outputs sound and cannot present numbers meaningfully, so it was not credited. Read what the data actually is before you name the device.

Flagged s23 P12 Q13c — printer/monitor to display weather data, not a speaker

Exam tips

A difference compares one feature
A "difference" or "compare" question needs the same feature on both sides. "RAM is volatile, ROM holds the start-up program" states two unrelated facts and does not compare. "RAM is volatile but ROM is non-volatile" puts one feature on both sides and scores.
"Explain" needs a because
Match the command word. State wants the term only. Describe wants what it is or does. Explain wants a reason — carry the second half with "because…". "A monitor is better" fails; "…because the readings can be read visually" completes it.
Never write a brand name
Examiners give no credit for a manufacturer or product name — not for a make of memory stick, printer or drive. Use the generic term every time: solid-state drive, memory stick, monitor, printer, hard disk drive.
Anchor on the direction of data
Input versus output is decided by where the data is going: input goes into the system to be processed; output is processed data presented to the user. If asked to justify a device, name it AND say why it suits that data type.

Revision notes