1.2- Memory and Storage Flashcards
What is primary storage?
“Main Memory”- RAM and ROM
Contain all the data and instructions the computer is currently using
Much faster than secondary storage.
What is RAM?
Volatile, read-write memory that holds data and instructions the computer is currently using
What is ROM?
Non-volatile, read only memory that holds boot up and basic instructions (eg BIOS). Can be updated by flashing. Normally fixed to motherboard.
How does ROM boot up a computer?
Instructions in ROM first check hardware and ensure everything is working (POST). ROM finds operating system on secondary storage, copies to RAM and puts OS in charge.
What is virtual memory?
When RAM is filled, computer allocates space on secondary storage to act as RAM. Oldest RAM applications are moved to virtual memory and then swapped back when they are used again.
Negatives of Virtual Memory
Needs to copy back into RAM to be read
If happens regularly can slow system dramatically
What is secondary storage?
Used as long term storage.
Contains OS, programs, documents and data.
Non volatile, so retains data while computer is off.
What are 3 types of secondary storage?
Optical: CD (<720MB), DVD (<8.4GB), Blu-Ray (<50GB). Uses lasers to read and write data while disc spins.
Very cheap, quite durable and very portable. Low capacity, easily scratched and low speeds.
Magnetic: HDD, magnetic tape (long term backup), floppy disk. Magnets charge particles to represent bits.
Very high capacity, good value. If bumped could be damaged, noisy and use more energy than SSD.
Solid State: Non-volatile RAM to store data when power is off. Normally much faster. No moving parts, more durable and use less energy. More expensive per GB and have limited number of write attempts.
How many bits in a nibble?
4 bits
How many bits in a byte?
8 bits
How many bytes in a kilobyte?
1000 bytes
How many kilobytes in a megabyte?
1000 kilobytes (1 million bytes)
How many megabytes in a gigabyte?
1000 megabytes
How many gigabytes in a terabyte?
1000 gigabytes
How many terabytes in a petabyte
1000 terabytes
Sound File Size =
Sample rate x duration (s) x bit depth
Image File Size =
Colour depth x image height (px) x image height (px)
Text File Size =
Bits per character x number of characters
What do binary shifts do?
Multiplies and divides binary numbers
x2 = shift left once
x4 = shift left twice
etc
What is an overflow error?
When there isn’t enough room for a result
Binary addition rules
0+1=1
1+1=0 carry 1
1+1+1=1 carry 1
What is a character set?
Where each letter/symbol utilised by the set is assigned a binary code so the computer can represent characters.
Name 3 character sets
ASCII
Extended ASCII
Unicode
How does number of bits per character affect total number of characters in a character set?
The more bits per character, the more characters can be used in the set as there are more options.
Eg. 7 Bit = 128 possible characters, 8 bit = 256 possible characters
How are images represented?
A series of pixels that each have a specific colour, which is assigned a specific binary code
How does colour depth affect quality and size of image?
Greater colour depth= Greater quality as more colours can be represented, greater image size
What is resolution
Number of pixels image contains. Greater resolution = greater quality, greater file size
What is sampling?
Taking measurements of the amplitude of the sound wave at regular intervals. This value assigned binary value in order to digitise an analogue sound wave.
What is sampling rate?
How many samples are taken per second - measured in Hz.
How does sampling rate affect sound?
Greater sampling rate = closer digital representation to actual sound
What is sampling size?
Amount of storage space allocated to storing each sample.
Sample size of 8 bits allows 256 different values.
What is bit rate?
Amount of storage required to store 1 second of sound.
Sampling frequency x Sample size
How does sample rate, bit depth and duration affect playback quality and file size?
Greater sample rate/ bit depth/ duration = greater file size
Greater sample rate/ bit depth = better playback quality
What is metadata?
Data about data.
Includes data about the file itself, such as file type, date created, author.
In images, includes resolution, colour depth, height x width of image.
What is lossy compression?
Lossy compression removes some of the file’s original data in order to reduce file size.
Eg. JPEG, MP3
What is lossless compression?
Reduces file size without removing any original data from file. Used when it is vital that the file can be restored to its original form.
Eg. ZIP
