1.2- Memory and Storage Flashcards
(36 cards)
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
