Storage and Memory

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Craig n DaveStorage and memory explained

Reference & Examples

Primary storage

RAM (Random Access Memory): volatile — loses all data when power off. Read/write. Stores currently running programs and data.
ROM (Read Only Memory): non-volatile — retains data without power. Read only (normally). Stores firmware/BIOS.
Cache: very fast memory built into or near the CPU. Stores frequently used instructions to reduce fetch time. Tiny capacity but fastest access.
L1 cache: fastest, smallest (on CPU). L2: slightly slower/larger. L3: larger, shared across cores.
More RAM → can run more programs simultaneously without swapping to disk.

Secondary storage types

Magnetic (HDD): spinning platters with magnetic coating. Slow (moving parts), large capacity, cheap per GB, non-volatile. Used for bulk storage.
Solid-state (SSD/Flash): no moving parts, transistors store charge. Fast, silent, low power, durable. More expensive per GB than HDD.
Optical (CD/DVD/Blu-ray): laser reads/writes pits and lands. Portable, limited capacity, slower, non-volatile.
Flash drives (USB): solid-state, portable. Used for data transfer.

Comparing storage types

Speed: Cache > RAM > SSD > HDD > Optical.
Capacity: HDD/Cloud > SSD > Optical > RAM > Cache.
Cost per GB: Cache > RAM > SSD > HDD > Optical.
Volatile: RAM, Cache. Non-volatile: ROM, HDD, SSD, Optical, Flash.
Choosing storage: consider speed needed, capacity required, cost, whether portability matters.

Data capacity units

Bit (b): 0 or 1. Byte (B): 8 bits. Nibble: 4 bits.
Kibibyte (KiB) = 1024 B. Mebibyte (MiB) = 1024 KiB. Gibibyte (GiB) = 1024 MiB.
Converting up: divide by 1024 (or 8 for bits→bytes).
Converting down: multiply by 1024 (or 8 for bytes→bits).
Exam: Edexcel uses binary prefixes (1024) not decimal (1000). Always use 1024.

Exam practice — 5 questions · 12 marks · 1CP2 Paper 1 style

1 markRAM characteristic1CP2 Paper 2

Which of the following best describes RAM?

A Non-volatile memory that stores the BIOS

B Volatile read/write memory that stores currently running programs and data

C Very fast memory built directly into the CPU for frequently used data

D Permanent storage for large files and the operating system installation

3 marksCompare HDD and SSD1CP2 Paper 2

A school is replacing all its computers. Give TWO advantages of SSDs over HDDs and ONE advantage of HDDs over SSDs. (3 marks)

Hint: SSDs are faster and more durable. HDDs win on cost per GB and available capacity.

+30 XP

1 markCache purpose1CP2 Paper 2

Why does the CPU use cache memory rather than always fetching from RAM?

A Cache has a larger capacity than RAM

B Cache is much faster than RAM — frequently needed instructions are kept close to the CPU to reduce fetch time

C Cache is non-volatile so data is not lost between tasks

D Cache can store more data types than RAM

4 marksData unit conversion1CP2 Paper 2

A sound file has a sample rate of 44,100 samples per second, bit depth of 16 bits, and duration of 60 seconds. (a) Construct an expression for the file size in bits. (b) Convert to MiB. Do not calculate — write the expression. (3 marks)

Hint: Sound file size = sample rate × bit depth × duration (in bits). Then: ÷8 for bytes, ÷1024 for KiB, ÷1024 for MiB.

+40 XP

1 markNon-volatile memory1CP2 Paper 2

Which of the following is non-volatile?

A RAM

B Cache

C SSD

D CPU registers

Primary storage

Secondary storage types

Comparing storage types

Data capacity units

Module complete! 🎉