1.2 - Memory and Storage Flashcards
Why do computers have primary storage?
To store programs that are currently running and need to be accessed by the CPU.
What does RAM store?
The operating system/software/data in use.
What are the key features of RAM?
Volatile; Read and Write; larger capacity than ROM
What does ROM store?
The bootstrap, the initial program that is run when the computer is switched on, these include: checking hardware is correctly installed, and loading BIOS.
What are the key features of ROM?
Non-volatile, read-only, smaller capacity than RAM
What is virtual memory?
Part of the hard drive used as an extension to RAM.
Why is virtual memory needed in a computer?
When there is not enough memory space left in RAM to store programs that you wish to open.
How does virtual memory work?
Programs are moved from RAM into virtual memory when they’re not needed. This frees up space in RAM to store the open programs. When these programs are needed again, they’re moved to RAM and programs are moved from RAM to virtual memory to free up space in RAM. Slow process.
What is secondary storage?
Non-volatile storage that is not directly accessible by the CPU
Why is secondary storage needed?
Storage of programs and data when the computer is switched off. Backup and archive of data files.
How does magnetic storage work?
Mechanical parts move over the disk surface to magnetically read and write data.
How does optical storage work?
Light used by lasers to read and write data.
How does solid state storage work?
Data is recorded onto solid memory chips, without any moving parts.
What are the advantages of magnetic storage?
Cheap, high capacity, quick write speeds.
What are the disadvantages of magnetic storage?
Lots of mechanical parts so not very durable and portable
What are the advantages of optical storage?
Cheap, portable, small
What are the disadvantages of optical storage?
Low capacity, slow write speeds, easily scratched, require CD reader
What are the advantages of solid state drives?
Durable - no moving parts; fast read-write speeds; no noisy fan, quick start-up times
What are the disadvantages of solid state drives?
Expensive, but same storage as magnetic disks, limited number of read-write cycles
Why must data be stored in binary?
Computers can only understand two states: power on and power off. This is represented by switches, and ‘1’s and ‘0’s.
How do we calculate the size of a sound file?
Sample rate * duration * bit depth
What is meant by sample rate?
Number of sound samples taken per second
What is meant by bit depth?
The number of bits needed to store each sample.
How do we calculate the size of an image file?
Colour depth * Image height * image width
What is meant by colour depth?
The number of bits needed to store each pixel
How do we calculate the size of a text file?
Number of characters * bits per character
What is a character set?
A set of letters, symbols, digits that can be represented by a computer.
How many bits is ASCII?
7
How many bits is extended ASCII?
8
How many bits is Unicode?
16
What is resolution?
The concentration of pixels within a specific area.
What are analogue sounds stored in?
Binary
What is metadata?
Information other than image data that is stored within an image file.
Examples of metadata?
Colour depth, resolution, date created, author
How is sound digitilised?
By repeatedly measuring the amplitude of the sound wave at regular and set intervals.
Why is compression needed?
Reduces download times (of files and data) of the Internet. Reduces storage capacity of a file.
What is the advantage of lossy compression?
Greater file size reduction (than lossless compression)
What are the disadvantages of lossy compression?
Data is lost and can’t be recovered; quality is compromised; can’t be used on text files or executable programs
What are the advantages of lossless compression?
No data lost, reversible, usable on all data types
What are the disadvantages of lossless compression?
Lower file size reduction than lossy compression
