1.2 – Memory and storage

Primary storage is the computer’s workspace for actively running programs providing fast access to data and instructions currently in use by the CPU without it computers would be slower as CPU would need to constantly retrieve data from slower secondary storage

Random Access Memory holds data and instructions the computer is currently working with such as the operating system running applications and open documents - RAM is volatile losing its contents when power is off

Read-Only Memory stores essential firmware for booting and operating the computer - ROM is non-volatile and cannot be written to during normal operation

Virtual memory is part of secondary storage used as extra RAM when physical RAM is full - operating system swaps data not currently needed from RAM to virtual memory allowing more programs to run

Secondary storage provides non-volatile long-term data storage so that data/files are retained when the computer is switched off

Solid-state - Optical - Magnetic

Uses electrical circuits to persistently store data with no moving parts providing high read/write speeds suitable for portable devices

Optical disks like CDs DVDs Blu-rays store data read by a laser - cheap per disk but low capacity and slower making them unsuitable for large-scale storage

Uses tiny magnetised regions to store data often with moving parts - cheap and suitable for large backups but not portable

solid-state drives and optical disks for capacity

Computers use binary because it has two states 0 and 1 mapping directly to electronic components like transistors making it simple to design hardware

Bit is 1 binary digit - nibble is 4 bits - byte is 8 bits

Kilobyte 1000 bytes - Megabyte 1000 KB - Gigabyte 1000 MB - Terabyte 1000 GB - Petabyte 1000 TB

Sample rate × duration in seconds × bit depth

Colour depth × image height in pixels × image width in pixels

Bits per character × number of characters

Number system humans use counting with digits 0 to 9 each digit having place value based on powers of 10

Number system with digits 0 and 1 each digit having place value based on powers of 2

Most significant bit is leftmost 1 with highest value - least significant bit is rightmost bit with lowest value

Add together the place values for every binary 1 using powers of 2

Use place value headers starting from the highest power of 2 placing 1 if value ≤ number subtracting and continuing until number is 0

0+0=0 - 1+0=1 - 1+1=0 carry 1 - overflow error occurs if result exceeds available bits

Uses digits 0-9 and letters A-F representing decimal 0-15 each hex digit represents 4 bits

Moving bits left or right losing bits at end zeros added at opposite end - left shift multiplies by 2 for each place - right shift divides by 2 for each place - used in graphics bitmasking compression encryption