Memory & Storage

Primary storage

Memory directly accessed by CPU (RAM, ROM, cache)

Secondary storage

Non-volatile storage used for long-term data (HDD, SSD)

Volatile memory

Loses data when power is turned off

Non-volatile memory

Retains data when power is off

RAM

Volatile memory storing data and instructions currently in use

ROM

Non-volatile memory storing boot instructions

Cache memory

Small, fast memory storing frequently used data

Virtual memory

Uses secondary storage when RAM is full

Role of RAM

Stores currently running programs and data for quick access

Role of ROM

Stores BIOS/boot program needed to start computer

Role of cache

Speeds up CPU performance by reducing access time

Why RAM is volatile

Uses temporary electrical signals which are lost when power off

Why ROM is non-volatile

Stores data permanently using non-erasable memory

Cache vs RAM

Cache is faster and smaller, RAM is slower but larger

Virtual memory disadvantage

Much slower than RAM, reduces system performance

Backing storage

Another term for secondary storage

Storage capacity

Amount of data that can be stored (bytes)

Storage units

Bit, nibble (4 bits), byte (8 bits), KB, MB, GB, TB

Binary representation

Data stored as 0s and 1s

Character set

Set of characters a computer can represent

ASCII

7-bit character set representing 128 characters

Unicode

Character set representing many languages using more bits

File size factors

Depends on resolution, colour depth, duration (for media)

Image resolution

Number of pixels in an image

Colour depth

Number of bits used per pixel

Higher resolution effect

Increases file size and image quality

Higher colour depth effect

Increases file size and colour detail

Sound sampling rate

Number of samples taken per second

Bit rate (audio)

Number of bits processed per second

Higher sampling rate effect

Improves sound quality but increases file size

Compression

Reducing file size

Lossy compression

Removes some data permanently to reduce size

Lossless compression

Reduces file size without losing data

Lossy example

JPEG images, MP3 audio

Lossless example

ZIP files, PNG images

HDD

Magnetic storage using spinning platters and read/write head

HDD advantage

Large capacity and cheaper per GB

HDD disadvantage

Slower and less durable due to moving parts

SSD

Solid-state storage using flash memory

SSD advantage

Faster, more durable, no moving parts

SSD disadvantage

More expensive per GB

Optical storage

Uses lasers to read/write data (CD, DVD, Blu-ray)

Optical advantage

Portable and cheap

Optical disadvantage

Lower capacity and slower speeds

Magnetic storage example

Hard disk drive, magnetic tape

Solid-state storage example

SSD, USB flash drive, memory card

[EXAM 6] Compare RAM and ROM

RAM is volatile and used to store currently running programs, while ROM is non-volatile and stores boot instructions needed to start the computer

[EXAM 6] Explain virtual memory

When RAM is full, part of secondary storage is used as virtual memory, but it is much slower, causing decreased performance

[EXAM 6] Compare SSD and HDD

SSD is faster, more durable, and uses less power due to no moving parts, while HDD is cheaper and has larger capacity but is slower and more prone to damage

[EXAM 6] Explain effect of increasing resolution and colour depth

Increasing resolution increases number of pixels, and increasing colour depth increases bits per pixel, both increasing file size

[EXAM 6] Explain difference between lossy and lossless compression

Lossy compression permanently removes some data to reduce file size, while lossless compression reduces size without losing any data