1.2 Memory and Storage Flashcards
Primary storage
Comprised of RAM and ROM. It holds data, programs and instructions that are currently in use.
Need for primary storage
The CPU can access data and instructions more quickly and easily than from secondary storage devices.
RAM
Random-access memory. Temporary storage of currently executing instructions and data - e.g. applications and the operating system.
-Volatile
-Read and write
-large compared to ROM
ROM
Read-only Memory. Stores startup instructions known as the bootstrap.
-Non-volatile
-Read only
-Small compared to RAM
Virtual memory
Using part of the hard disk as if it were random-access memory. Allows more applications to be open than physical memory can hold.
-Programs are transferred out to virtual memory from RAM when not being executed to free up space in primary storage
-transferred back when needed
Secondary storage
Permanent storage of instructions and data not currently in use by the processor. Stores the operating system, applications and data. Read-and-write and non-volatile.
Need for secondary storage
-ROM is read-only and RAM is volatile
-It is the storage of programs and data when the power is turned off
-and is semi-permanent storage that can change
Common types of storage
-Optical (DVDs, CDs)
-Magnetic (Hard disk)
-Solid state (USB)
Advantages of optical storage
-Thin
-Lightweight
-Portable
Disadvantages of optical storage
-Low capacity compared to others
-slow to access
-loses data when scratched
Advantages of magnetic storage
-Quick access data
-high storage capacity
Disadvantages of magnetic storage
-Has moving parts, and will eventually fail
-slower access than solid state
Disdvantages of solid state storage
-Medium storage capacity
-limited number of read-write cycles
-expensive
Advantages of solid state storage
-small, lightweight
-fast access time
-no noise - no moving parts
-low power
Units of data storage
-Bit (1)
-Nibble (4 bits)
-Byte (8 bits)
-Kilobyte (1000 bytes)
-Megabyte (1000 KB)
-Gigabyte (1000 MB)
-Terabyte (1000 GB)
-Petabyte (1000 TB)
Binary numbers
A numbering scheme with only two possible values for each digit, 0 and 1.
Base 2
8 bit binary
2^8 = 256 combinations
-numbers 0-255
Denary numbers
A numerical system of notation that uses 10 as its base. The ten decimal base digits are 0-9.
Hexadecimal
A numerical system that uses 16 as its base. The 16 hex base digits are 0-9 and A-F. Computers don’t use it but used to represent large binary numbers into a smaller number of digits for humans.
Binary addition
128,64,32,16,8,4,2
Rules:
-0+0=0
-0+1=1
-1+1=1 carry 1
-1+1+1 = 1 carry 1
Practice binary addition
Binary overflow
The generation of a number that is too large to be represented by the device intended to store it.
Convert between denary and 2 digit hexadecimals
Practice converting
Binary shifts
Shift left - times by 2
Shift right - divided by 2
Character sets
Defined list of characters recognized by the computer hardware and software, with each character being represented by a single number.
Types of character sets
-ASCII 7-bit character set - 2^7 = 128 combinations
-Extended ASCII 8-bit character set - 2^8 = 256 combinations
-Unicode 24-bit character set - 2^24 = 16 million combinations
How images are stored
Bitmap - image made up of pixels, each square has a binary value - photographs
Vector - mathematics to store the square are stored - technical, drawings, logos, clipart
Metadata
A collection of data that describes and provides information about other data.
-Such as width, height, colour depth, colour palette
Colour/ bit depth
Number of bits needed to store each pixel.
Photos are usually stored in 24 bit colour depth = 2^24 = > 16 million colours
Equation for the size of image file
Image height * image width * colour depth
Converting music to digital
Height of the analogue signal is measured/ sampled at regular intervals and stored as binary as a digital signal
Sample rate
How often (frequency) you record the amplitude of a sound wave.
The more often a sample is recorded, the smoother the playback will sound.
Measured in hertz (Hz) - E.g. 44,000 Hz = 44,000 samples taken /second
Sound - Bit depth
How many gradations of amplitude can be represented in a digital wave form
Calculating sound file size
Sample rate * duration (s) * bit depth
Use of compression
-Reduces the size of a file so it takes up less space
-maximizes the amount you can store on a device
-smaller files are quicker when transferred over the internet
-lossy and lossless
Lossy compression
A compression method where the data in a file is removed and not restored to its original form after decompression
-Used for image, music, video files
-more effective than lossless
Lossless compression
Reduces file size with no loss of data
-all original data can be recovered when the file is uncompressed
-usually used for texts and spreadsheet files
