Memory And Storage Flashcards
Computer systems need …
both primary and secondary storage to operate
What are the properties of primary storage
-Volatile (with the exception of ROM)
-Small capacity
What are the properties of secondary storage
-Non-volatile
-Large capacity
Why do you need primary storage
A computer needs primary storage because access times are considerably faster than secondary
What is RAM
RAM (Random Access Memory) is primary storage that is directly connected to the CPU and holds the data and instructions that are currently in use
RAM is …
volatile
What are the properties of RAM
-very fast working memory, much faster than secondary storage
-RAM is read/write which means data can be read from and written to
-It has a much larger capacity than ROM
What is ROM
ROM (Read Only Memory) is primary storage that holds the first instructions a computer needs to start up (Bootstrap)
ROM contains the …
BIOS (Basic Input Output System)
ROM is …
non-volatile
What are the properties of ROM
-It is faster than secondary storage but slower than RAM
-ROM is read only which means data can only be read from
- it has a much smaller capacity than RAM
What is virtual memory
Virtual memory is an extension of primary storage (RAM) located on secondary storage
Why is virtual memory used
where RAM is close to being full, virtual memory can be used so that the computer remains operational
What are the properties of virtual memory
It is much slower than RAM and it’s use will impact negatively on system performance
Why do you need secondary storage
A computer needs secondary storage for long term storage of programs and data that are currently not in use
Secondary storage holds …
the programs and data whilst the computer is turned off
Performance of secondary storage is
slower than primary storage
What are the characteristics of secondary storage
-Capacity
-Speed
-Cost
-Portability
-Durability
-Reliability
What are the 3 types of secondary storage
-Magnetic
-Solid State
-Optical
What is magnetic storage
Magnetic storage is a type of non-volatile media that uses magnets to store binary 0s and 1s
What are the advantages of magnetic storage
-Capacity - High storage
-Cost - Low per gigabyte
-Speed - Moderate read/write access
What are the disadvantages of magnetic storage
-Durability - Moving parts can get damaged if dropped
-Portability - Heavy & bulky making them less convenient for transport
-Reliability - Prone to mechanical failure
-Noise - Loud (spinning disks)
What is solid state storage
Solid state storage is a type of non-volatile media that uses electronic circuits to store binary 0s and 1s
What are the advantages of solid state storage
Capacity - Medium/high storage
Speed - Very fast read/write access Reliability - Limited read/write cycles
Durability - No moving parts
Portability - Small and no moving parts
Noise - Silent
What are the disadvantages of solid state storage
-Cost - Very high per gigabyte
-Reliability - Limited read/write cycles
What is optical storage
Optical storage is a type of non-volatile media that uses lasers to burn the surface of a disk, creating pits and lands suitable for storing binary 0s and 1s
What are the advantages of optical storage
Cost - Very low per gigabyte
Durability - No moving parts
Portability - Small
Noise - Silent
What are the disadvantages of optical storage
-Capacity - Very low
-Speed - Very slow read/write access
-Reliability - Prone to scratches
Computers use binary numbers to …
represent data
What are units of data
Why does data have to be converted to binary to be processed by a computer
A computer is built using switches that can either be on or off ( 1= on, 0= off)
What is the formula to calculate the text file size
Bytes per character x Number of characters
What is the formula to calculate the image file size
Resolution x Colour Depth
What is the formula for resolution
Resolution = Width x Height
What is the formula to calculate the sound file size
Sample Rate x Duration in seconds x Bit Depth
How to convert Denary to binary and binary to Denary
Use the table
What is an overflow error
An overflow error occurs when the result of a binary addition exceeds the available bits
What is hexadecimal
Hexadecimal is a number system that is made up of 16 digits
A left shift …
multiplies a binary number by 2 (x2)
A right shift …
divides a binary number by 2 (/2)
What is a character set
A character set is a defined list of characters that can be understood by a computer
What are the Two common character sets
-ASCII
-UNICODE
What is ASCII
What are Limitations of ASCII
has a limited number of characters which means it can only represent the English alphabet, numbers and some special characters
What is UNICODE
UNICODE is a character set and was created as a solution to the limitations of ASCII
What are the properties of UNICODE
-UNICODE uses a minimum of 16 bits, providing 216, representing 65,536 characters
-UNICODE can represent characters from all the major languages around the world
What are the properties of ASCII
ASCII uses 7 bits, providing 27 unique codes (128) or a maximum of 128 characters it can represent
What is a bitmap
A bitmap image is made up of squares called pixels
What is a pixel
-A pixel is the smallest element of a bitmap image
-Each pixel is stored as a binary code
What is a binary code
Binary codes are unique to the colour in each pixel
What is resolution
Resolution is the total amount of pixels that make up a bitmap image
What is colour depth
Colour depth is the number of bits stored per pixel in a bitmap image
What Is the formula to calculate the amount of colours
2^n (n = colour depth)
What is the impact of resolution and colour depth
As the resolution or colour depth increases, the bigger the size of the file
What is metadata
Metadata is additional information stored with the image
How is sound sampled & stored
-analogue sound waves are converted to digital sound waves by Analogue to Digital conversion
-measure the height of the analogue sound wave
-Each sample generates a value which can be represented in binary and stored
-Using the samples a computer is able to create a digital version of the original analogue wave
-The digital wave is stored on secondary storage
What is sample rate
Sample rate is the amount of samples taken per second of the analogue wave
Samples are …
-taken each second for the duration of the sound
-The sample rate is measured in Hertz (Hz)
What is bit depth
Bit depth is the number of bits stored per sample of sound
What effect do sample rate and bit depth have on playback quality
higher sample rate = more detail, better sound quality
-higher bit depth = bigger range, better sound quality
What effect do sample rate and bit depth have on file size
-higher sample rate = more data, larger file size
-higher bit depth = more data per sample, larger file size
What is compression
Compression is reducing the the size of a file so that it takes up less space on secondary storage
What is lossy compression
Lossy compression is when data is lost in order to reduce the size on secondary storage
What are the properties of lossy compression
-Lossy compression is irreversible
-Lossy can greatly reduce the size of a file but at the expense of losing quality
-Lossy is only suitable for data where reducing quality is acceptable
What is lossless compression
Lossless compression is when data is encoded in order to reduce the size on secondary storage
What are the properties of lossless compression
-Lossless compression is reversible, the file can be returned to its original state
-Lossless can reduce the size of a file but not as dramatically as lossy
-Lossless can be used on all data but is more suitable for data where a loss in quality is unacceptable
