1.2 Memory And Storage Flashcards
What does primary storage consist of
RAM (random access memory)
ROM (read only memory)
What is ROM
Small piece of read only memory
Non volatile (contents remain when power turned off)
Programs may be stored in it in embedded systems
Stores instructions/data that never need to be changed eg = first instructions for computer when its turned on (bootstrap)
Can’t overwrite its contents
What’s RAM & whys it needed
Needed to Temporarily store programs, instrutions and data
Volatile (contents lost when power is turned off)
Read and write
Much faster than the hard disk
Holds operating system, programs and data in use by CPU when computer’s running
How does virtual memory work
Needed when not enough physical RAM to store open programs
Held on hard disk
Programs swapped to virtual memory from RAM when not currently in use
Programs swapped back to RAM from virtual memory when they’re needed
Why is secondary storage needed
For longer term storage of files and data because it’s non-volatile
What’s secondary storage needed for
Storage of programs when power is turned off
Long term storage
Backup of data files
What’s optical storage + examples
CD, DVD, blu-ray
Low capacity compared to other types of storage
Slow to access data
Lightweight + portable
What’s magnetic storage + examples
Hard disk drive, magnetic tape
High storage capacity
Quick to access data
Has moving parts - eventually fail
What’s solid state storage + examples
SSD, memory sticks, flash memory cards, SD cards
Medium storage capacity
Very quick to access data
No moving parts - very reliable/durable
Limited number of read/write cycles
Expensive per gig compared to other types of storage
Why do we use binary
A CPU is made of millions of transistors that can be in one of two states - on or off
How do you calculate text files sizes
Bits per character x number of characters
How do you calculate image file size
Colour depth x image height x image width
How do you calculate sound file size
Sample rate x duration in seconds x bit depth
What are the placeholder headings in binary
128 64 32 16 8 4 2 1
Why do we use hexadecimal
Binary can be difficult to work with, its shorter, it can easily be converted to/from binary as theres 1 hex digit per nibble and hex is less susceptible to errors
What letters represent 10 - 15 in hex
10 = A
11 = B
12 = C
13 = D
14 = E
15 = F
What are the hex placeholder
16 1
What do you do when you shift left in binary
Multiply
What do you do when you shift right in binary
Divide
What is a character set
A defined list of characters recorded by the computer
What is the term character set used for
To describe the possible characters that can be represented in a computer system
What is ASCII
A 7 bit character set with 128 characters (2^7)
What is extended ASCII
An 8 bit character set with 256 characters (2^8)
What is Unicode
A 16 bit character set with 65,536 characters (2^16)
How does an overflow error happen
When the result of a binary addition is greater than 8 bits
What’s a pixel
The smallest part of an image
What’s metadata
Data about data eg = height, width, colour depth, type of image, when created, date/time, location etc.
How must analogue sound be recorded
Digitally in binary
What affects sound quality
How the often the height is recorded (sample rate) and the accuracy which it recorded (bit depth)
What affects a sounds file size
Duration of the recording
Calculate the total number of bits in a sound file size
Number of samples per second x number of bits per sample x length of sample in seconds
What is bit depth
The number of bits stored per sample
What is sample rate
Number of samples stored per second
How is analogue converted to digital
An analogue sound wave is sampled, the height of the wave is measured at regular time intervals. Each samples stored as a binary number
What’s compression
Reducing the number of bits in a file
What does compression do
Makes file size smaller
Makes data transfer to the file quicker
Faster upload/download speed
Lossy compression characteristics
- Some data is lost permanently - cant be recovered
- greatly reduces file size
- reduces image, video or sound quality but not enough for a human to notice
- cant be used on text and program code as parts will be missing
Lossless compression characteristics
- no data is lost - encoded differently
- can be turned back to original format
- usually less effective than lossy t reducing file size
- most suitable for text documents and program code as
