1.2 Units of Information Flashcards
What does Primary storage do
It holds the data and instructions which the CPU needs access to while a computer is running.
What does Primary Storage Consist of
Random Access Memory (RAM)
Read Only Memory (ROM)
Registers & Cache
What is RAM
- Holds the operating system, programs and data in use by the CPU when the computer is running.
- Volatile (contents lost when the power is turned off).
- Read and write.
- Large in comparison to ROM.
What is ROM
- Holds the first instructions for when the computer is first turned on known as the bootstrap.
- Programs may by stored in ROM in embedded systems.
- Non-volatile (contents remains when power is turned off)
- Read only
- Small in comparison to RAM
What is Virtual Memory used for
- Virtual memory is needed when there is not enough physical RAM to store the open programs.
- Virtual memory is held on the hard disk.
- Programs are transferred out to virtual memory from the RAM when they are not currently being executed.
- Programs are transferred back to RAM from virtual memory when they are needed.
What is secondary storage needed for
- Secondary storage is needed because ROM is ready only and RAM is volatile.
- Second storage is needed for:
Storage of programs and data when the power is turned off. Semi-permanent storage of data that can change.
Backup of data files.
Archive of data files.
What are the common types of Storage
Optical (CD-R, DVD-R)
Magnetic (Hard disk drive)
Solid state (SSD, Memory stick)
What are qualities of Optical storage
Low capacity compared to other types of storage.
Slow to access data.
Thin, lightweight and portable.
What are qualities of Magnetic Storage
High storage capacity.
Quick to access data.
Has moving parts, which eventually fail.
Hard disks perform better if they are defragmented
What are qualities of Solid-State Storage
Medium storage capacity.
Very quick to access data.
No noise. No moving parts, very reliable.
Low power.
No need to defragment.
Limited number of read/write cycles.
Expensive compared to other types of storage.
How do you calculate text file size
Bits per character x number of character
How do you calculate image file size
Colour depth x image height px x image width px
How do you calculate sound file size
sample rate x duration in second x bit depth
Why do computers use Binary
- Easier to manufacture
- cheaper
- more reliable
What is a character set
a defined list of characters recognised by the computer
What is ASCII
7 bit character set with 128 characters (2^7)
What is Extended ASCII
8 bit character set with 256 characters (2^8)
What is UNICODE
24 bit character set with > 6 million characters (2^24)
What can images be stored as in binary
Bitmap
Vector
What are Bitmap pictures
Pictures constructed from coloured squares called pixels
What are Vector pictures
Pictures that store the mathematics to draw coloured shapes
What is the general formula to find the number of colours
2^n (n=number of bits for each pixel)
What is metadata
additional data stored with the image to define the width, height, colour depth, and colour palette
How do you calculate a sound file size
number of samples per second x number of bits per sample x length of sample in seconds
What is a sound file
the total number of bits in a sound
What is bit depth
The number of bits stored per sample
What is sample rate
The number of samples stored per second
What is compression
Reducing the number of bits in a file
Making the storage capacity of the file lower
Making data transfer of the file quicker
What is lossy compression
Some of the data is lost and cannot be recovered.
Greatly reduces the file size.
Reduces the quality of the image/sound.
Suitable for images, sound and video.
Cannot be used on text and executable files.
What is lossless compression
None of the data is lost, it is encoded differently.
Can be turned back into original format.
Can be used on all types of data.
Is usually less effective than lossy compression at reducing the file size.
Most suitable for documents and executable files.
