1.2 Memory & Storage Flashcards
Random Access Memory (RAM)
Holds the operating system, programs and data in use by the CPU when the computer is running.
Volatile memory (loses data when power is lost).
Quick read & write times.
Larger capacity compared to ROM.
Read Only Memory (ROM)
Holds the essential programs, like those needed to be run in order to boot the computer.
Non-volatile memory (keeps data when power is lost).
Read only, so can’t be changed once programmed.
Small capacity compared to RAM.
Virtual Memory
Used when there isn’t enough space in RAM for all the programs and data you are currently working on.
Virtual memory is held on the hard disk.
Programs are transferred out to virtual memory from RAM when they are not currently being executed.
Programs are transferred back to RAM from virtual memory when they are needed.
Secondary Storage
Non-volatile storage not directly connected to the CPU. It is needed to keep programs and data indefinitely.
Optical Storage
Advantages:
Lightweight: good portability.
Disadvantages:
Small capacity
Slow to access data.
Low durability.
Examples: DVD, CD, Blue-Ray Discs
Magnetic Storage
Advantages:
High storage capacity.
Quick to access data.
Cheap.
Disadvantages:
Has moving parts, which eventually fail.
Not very durable.
Not very portable.
Examples: HDD (Hard-disk drives), Magnetic tape, Floppy disk drives
Solid-State
Advantages:
Very fast.
Very reliable as they are non-mechanical.
Silent.
Low power.
Disadvantages:
Can be expensive.
Generally have a smaller capacity than magnetic.
Examples: USB Flash Drive, SD Cards
Binary
A single 1 or 0 is a binary digit (bit).
A nibble = 4 bits e.g. 0110
A byte = 8 bits e.g. 0110 1100
A Kilobytes (kB) = 1000 bytes
A Megabytes (MB) =1000 kilobytes
A Gigabyte (GB) = 1000 Megabytes
A Terabyte (TB) = 1000 Gigabytes
A Petabyte (PB) = 1000 Terabytes
Sound Sample Rate/Frequency
The number of samples taken per second, measured in Hertz (Hz). The higher this is, the higher the quality of the sound and the larger the file size.
Sound Bit Depth
The number of bits available for each sample. The higher the number of bits, the greater the quality of the sound, and the larger the file size.
File Size In Bits Calculation
Sample Rate x Bit Depth x Duration (secs) x number of channels (1 mono, 2 stereo)
Lossy Compression
Some of the original data is lost.
Greatly reduces the file size.
Not used where all data is important (e.g. code), but where the only consequence is loss of quality (e.g. images and video).
JPEG and MP3 are two lossy compression algorithms – partly work by removing sounds/colours we recognise least.
Lossless Compression
None of the data is lost (can be turned back into original format), but it is rearranged to reduce the file size.
Is usually less effective than lossy compression at reducing the file size.
Most suitable for documents and random text. E.g. PDF and GIF
Can be done with Run Length Encoding (RLE) – Replacing repeated data (‘runs’) with data pairs.
