1.2 Memory and Storage Flashcards
Why do computers need primary memory?
The read and write speed on a hard disk is very slow compared to Main Memory yet the cost of faster speeds means that primary memory doesn’t have enough storage space
Features of RAM
- Random Access Memory
- Stores part of the OS and software in use
- Can be read from and written to
- Volatile
Features of ROM
- Read Only Memory
- Stores start-up programs, various firmware for the control of the components, bootstrap which tells the computer where to find the OS on the hard drive and Basic Input/Output System (BIOS) which controls the configuration of components
- Can only be read from
- Non-volatile
When is virtual memory needed?
When there isn’t enough physical RAM space to store open programs
Where is virtual memory stored?
On the hard disk
How does virtual memory work?
- Programs are transferred out to virtual memory from the RAM when they aren’t currently being executed
- Programs are transferred back to RAM when they’re needed
Optical storage
Lasers read and write data using light
Magnetic storage
Mechanical parts e.g. a driver head move over the disk to read and write data magnetically
Features of optical storage (Capacity, Speed, Portability, Durability, Reliability, Cost)
- Bad compared to others
- Bad, accessed in a spiral
- Good
- Bad, prone to scratches
- Medium, can become damaged easily
- Good, cheap to buy in bulk
Features of magnetic storage (Capacity, Speed, Portability, Durability, Reliability, Cost)
- Good
- Medium, can only be read sequentially
- Medium, moving when powered on can damage the device
- Medium, moving parts eventually fail
- Medium, can become damaged or moving parts can fail
- Good, cheaper cost per gigabyte than solid state
What are the features of virtual memory?
- Cheaper than increased RAM
- Prevents error message ‘out of memory’ while programs and files remain open
- Takes more time to access than data stored in RAM due to transfer time
Features of solid state storage (Capacity, Speed, Portability, Durability, Reliability, Cost)
- Medium
- Good, data doesn’t need to be accessed sequentially
- Good
- Bad, limited number of read/write cycles
- Good, no moving parts
- Medium, price is decreasing as technology improves
Nibble
4 bits
Byte
8 bits
What is the order of units of data?
kB, MB, GB, TB, PB
0+0
0
1+0
1
1+1
0 carry 1
1+1+1
1 carry 1
Shift left
Multiply by 2
Shift right
Divide by 2 (empty positions are filled with 0s resulting in a loss of accuracy)
Most significant bit
Largest power of 2
Least significant bit
Smallest power of 2
Binary to hex and vice versa
Each nibble converted separately e.g. 11011001=D9
Denary to hex and vice versa
Divide by 16 for first digit value, remainder is second digit value e.g. 217=D9
Character set
A logically ordered set of all characters that can be encoded using a given number of bits
American Standard Code for Information Interchange
7 bits (128 characters)
Extended ASCII
8 bits (256 characters)
Unicode
16 bits (63,536 characters) used for all languages of the world and some emojis
What are images made up of?
Pixels
The more pixels per inch, the greater the resolution but…
The greater the file size since more data needs to be stored
Colour depth
The number of bits per pixel
The more colours represented in an image…
The more bits needed per pixel and therefore the greater the file size
Metadata
Data about data e.g. file type, time and date of creation, author, file size, image dimensions, image resolution, colour depth
What is used to log sound in binary form?
Analogue-to-Digital Converter
Sample resolution
The number of bits used to stored each sample
The greater the sample resolution…
The greater the accuracy and therefore quality but also file size
Sample rate
Frequency in Hz with which sound is recorded
The greater the sample rate…
The greater the quality and file size
Features of lossy compression
- Removes data that can go unrecognised to the user
- Less accuracy
- Smaller file size
- Used for images (jpg), audio (mp3), video and GIFs
Features of lossless compression
- Identifies and encodes repeated sections of data so that they can be represented efficiently
- More accuracy
- Larger file size
- Used for documents and PNGs
Why is secondary storage needed?
RAM is volatile and ROM is read-only therefore it is needed to stored programs and data when the computer is powered off
Image file size (bits)
Image height x image width x colour depth + metadata
Sound file size (bits)
Sample rate x bit depth x duration + metadata
