1.2 Memory and Storage Flashcards
Primary Storage
Memory that the CPU can access very quickly
Need for primary storage
For data it needs to access quickly
Examples of things stored in primary storage
Operating System
BIOS
Boot up instructions
Types of primary storage
ROM
RAM
Purpose of ROM in a computer system
Non - volatile
Contains BIOS for the boot process
Purpose of RAM in a computer system
Volatile
Operating system is copied into RAM from secondary storage when computer boots up
CPU can access quickly - stores data, files, and programs that are being used
ROM full form
Read-only memory
RAM full form
Random access memory
Volatile memory
Temporary
Needs power to retain data
Non - volatile memory
Permanent
Retains. data when there is no power
BIOS
Basic Input Output System
Instructions a computer needs to properly boot up
Virtual Memory
When RAM gets full, the computer moves less recently used data into a section of secondary storage (virtual memory)
For the CPU to read data in virtual memory, it needs to be swapped back into RAM
When is virtual memory needed?
When too many applications are running at once
Disadvantage of Virtual Memory
Makes a computer slow to respond when switching between applications (swapping them in and out of RAM)
Secondary Storage
Where data is stored when not in use
Need for secondary storage
To store files and programs
Common types of secondary storage
Optical
Magnetic
SSD
HDD
Hard Disk Drives (HDDs)
Stack of magnetised metal disks that spin
Have a read-write head which can read + write data
Solid State Drives (SSDs)
No moving parts = silent
Use a type of flash memory
Higher read-write speed than HDDs
Advantages of HDDs
Cheap
High capacity
Longer read-write life than SSDs
Advantages of SSDs
Faster
Don’t need to be defragmented (slows them down!)
Shock - proof
Silent
Optical Storage
Uses light to store data
Examples of optical discs
CD
DVD
Blu-ray
Types of Optical Discs
Read only (e.g. CD-ROM)
Write once (e.g. CD-R)
Rewritable (e.g. CD-RW)
Why use of optical discs is declining
Streaming services have become popular e.g. Netflix
Modern devices e.g. phones don’t have optical drives
Disadvantages of Optical Storage
Low capacity
Slow read/write speed
Poor reliability
Scratches
Advantages of Optical Storage
Cheap
Portable
Not affected by water or shock
Advantages of Magnetic Tapes
Large capacity
Cheap
Fast rad/write speed
Where are magnetic tapes used?
In archives of large organisations
Disadvantages of Magnetic Tape
Read/write sequentially -> difficult to find a specific piece of data on it
Bit
Single binary digit (1 or 0)
Nibble
4 bits
Byte (B)
8 bits
Kilobyte (KB)
1000 Bytes
Megabyte (MB)
1000 Kilobytes
Gigabyte (GB)
1000 Megabytes
Terabyte (TB)
1000 GIgabytes
Petabyte (PB)
1000 Terabytes
Why does data need to be converted to binary so that the computer can read it?
Computers only process binary digits
Binary digits represent the flow of electricty
How do computers process alphanumerical character?
Character sets
Character Set
A collection of characters that a computer recognises due to their binary representation
More number of bits per character = more characters
What happens when you press a key on your keyboard?
Sends a binary signal to the computer telling it which key was pressed
The computer uses the character set to translate it into binary
Examples of Character Sets
ASCII
Unicode
ASCII
7-bit binary code -> 128 characters
Unicode
Covers all major symbols and languages
Uses multiple bytes
First 128 codes are the same as ASCII
How are images stored?
Made up of pixels
Types of images
Bitmap
Vector
What is the colour of each pixel represented by?
Binary
Colour Depth
The number of bits used for each pixel
How to work out the total number of colours
2*n(number of bits per pixel)
Image Resolution
Number of pixels in the image
How to work out image resolution
Width x Height
How does colour depth and resolution effect the quality of the image?
Higher resolution and higher colour depth = better quality of image
How to work out file size
Image resolution x colour depth
Width x height x colour depth
Metadata
Data about data
Information stored in an image which helps the computer recreate the image on screen
Examples of things stored in metadata
File format
Height
Width
Colour Depth
Resolution
Sampling
The process of converting from analogue to digital
How can analogue sound be converted into digital data?
Analogue to digital converters
Sample Rate
How many samples are taken in a second
In Hz
Bit depth
Number of bits available for each sample
How to calculate file size
Sample Rate x Bit Depth x Length
How does sample rate + bit depth effect the playback quality
Higher sample rate = better quality
Higher bit depth -> the digital file also picks quieter sounds = better quality
How does sample rate + bit depth effect file size
Higher bit depth + sample rate = higher file size
Data Compression
To make file sizes smaller
Uses of Data Compression
Takes up less storage
Streaming + downloading files from the Internet is quicker as less bandwidth is used
Web pages download quicker
Email services have restrictions on file size
Types of Compression
Lossy
Lossless
Lossy Compression
Permanently removes data from the file
Lossless Compression
Temporarily removes data from the file to store it, and restores it when it is opened
Advantages of Lossy
High file size reduction
Use up less bandwidth -> can be streamed and downloaded quickly
Commonly used
Disadvantages of Lossy
Loses data -> file cannot be reverted back to the original
Cannot be used on text files
Highly reduce quality of image
Examples of Lossy file types
MP3
AAC
JPEG
Advantages of Lossless Compression
Data is only removed temporariliy -> when opened there is no reduction in quality
Can be used for text files
Disadvantages of Lossless Compression
Only slight reduction in file size
Examples of Lossless file types
FLAC
TIFF
PNG
