1.2 - memory & storage Flashcards
Primary storage
Also known as memory. Holds the data, programs and instructions currently in use. (includes RAM and ROM)
RAM (random access memory)
Stores programs and data before they are
processed by the CPU. Read/write memory, meaning the contents can be changed. The contents are lost when the computer is turned off (Volatile)
ROM (read only memory)
Data can be retrieved but not changed and the
contents are not lost when the computer is turned off. Used to store programs for an embedded system
Volatile memory
Data stored in volatile memory is lost when the computer is turned off
Non-volatile memory
Data stored in non-volatile memory is not lost when the computer is turned off
Virtual memory
Space on the computers’ hard drive is used as main memory (extra RAM), if RAM is full. Virtual memory is slower than main memory
Optical storage
A type of secondary storage which stores data on a spinning disk (made of plastic or metal). Data is read from and written to the disk using a laser.
Magnetic storage
A type of secondary storage which uses magnetic fields to store data. A read/write head reads and writes data from the media.
Solid state storage
A type of secondary storage which uses flash memory to store data. They have no moving parts and are much faster than optical or magnetic storage.
HDD (hard disk drive)
A magnetic storage drive which can store large amounts of data and is often the main method of secondary storage in personal computers. The drive contains a number of internal disks and a read/write head used to read and write data.
DVD (Digital Versatile Disk)
A high capacity optical storage disk commonly used for video storage. A range of capacities are available up to 17GB
CD (Compact Disk)
An optical storage disk is regularly used to store music. Capacity is typically around 800mb
SSD (Solid State Drive)
A solid state storage drive which carries out the function of a HDD. They are much faster than HDDs and less easy to damage as they have no moving parts. They are also more expensive and usually lower capacity.
Capacity
the amount of storage available
Cost
the price per gigabyte
speed
how fast the read/write process is
durability
how likely the storage is to break if it is dropped or worn over time
reliability
how well the storage will function over time
Portability
how easy it is to transport the storage device
What are the advantages and disadvantages of magnetic storage?
Advantages:
- capacity - high storage (100 terabytes)
- cost - low per gigabyte (0.018)
- speed - moderate
Disadvantages:
- durability - moving parts easily damaged
- portability - heavy and bulky so less convenient
- reliability - often have mechanical failure
What are the advantages and disadvantages of solid state storage?
Advantages:
- capacity - medium/high storage (128GB - 4TB)
- speed - very fast
- durability - no moving parts to damage
- portability - small and lightweight
Disadvantages:
- cost - high per gigabyte (0.15 to 0.50)
- reliability - limited read/write cycles
What are the advantages and disadvantages of optical storage?
Advantages:
- cost - low per gigabyte (0.001)
- durability - no moving parts
- portability - small and no moving parts
Disadvantages:
- capacity - very low (700 MB - 25 GB)
- speed - very slow read/write access
- reliability - prone to scratches
what is the ascending order of storage units?
- bit - either binary 0 or 1
- nibble - 4 bits (half a byte)
- byte - 8 bits
- Kilobyte (KB) - 1000 bytes
- Megabyte (MB) - 1000 KB
- Gigabyte (GB) - 1000 MB
- Terabyte (TB) - 1000 GB
- Petabyte (PB) - 1000 TB
Binary
A number system used by computers. It contains only two symbols, 0 and 1. It is also known as base 2.
Denary
The number system most often used by people. It uses the digits 0 to 9 and is also known as base 10 or decimal.
Overflow Error
This happens when not enough space has been allocated to store the results of a calculation. For example, if one byte has been allocated but the result is 9 bits long.
Hexadecimal
Uses 16 symbols: 0 to 9 and A to F. Letters are used to represent values 10 to 15. Also known as base-16
Binary Shift
A process used to preform math on binary numbers. It involves moving all the digits to the left or right.
Most Significant Bit
The furthest left digit in a string of binary numbers, its position means it
has the highest value.
Least Significant Bit
The furthest right digit in a string of binary numbers, its position means it has the lowest value.
Character
A single symbol, for example a letter, number or punctuation mark.
Character Set
A system for representing characters in binary, each character is assigned a unique binary number.
ASCII
American Standard Code for Information Interchange. A 7 bit character set used to represent characters.
Unicode
A much larger character set created to overcome the limited number of characters available in ASCII. It includes many different language characters and other symbols like emojis.
Pixel
Short for Picture Element. Pictures on a computer are divided into a grid, with each square in the grid being one pixel which can be a single colour.
Metadata
Additional data about a file such as when it was created or who created it. Commonly used with photos to store things like the make of camera or location the photo was taken.
Colour Depth
The amount of bits available for colours in an image. The higher the colour depth the more colours available and therefore the more detailed the image will appear.
Resolution
The number of pixels an image is divided into. The higher the resolution, the more pixels in the image and the clearer it will be.
Sample Rate
The number of samples taken in one second. This is measured in hertz (Hz) - 1Hz is one sample per second. The higher the sample rate, the more samples per second and therefore the higher the quality of the file.
Bit Depth
The number of bits available for each sample. The higher the bit depth, the more bits available and therefore the better the quality.
Analogue
A continuously varying signal, usually represented as a curved line. Examples include sound or temperature recordings.
Compression
A way of reducing the size of a file. It is often used with photos, music and video files.
Lossy Compression
A compression method which reduces the file size by removing certain data. The original file cannot be restored from the compressed version but the file size is reduced by more than with lossless compression.
Lossless Compression
A compression method which reduces the file size without losing any data. The original file can be restored from the compressed version, but the file size is not reduced by as much.
