1.2 Memory and storage Flashcards
Define RAM
Random Access Memory is the main memory for the computer. It can be read and written to. RAM is volatile. RAM stores data, files and programs currently in use. Directly accessed by the processor.
Define ROM
Read Only Memory is non-volatile. ROM comes on a small factory made chip Built into the motherboard. It stores the instructions needed to boot (BIOS).
Define volatile
Volatile memory is temporary memory. It requires power to retain its data. Non-volatile is permanent memory; it keeps data even when the power is off.
Define virtual memory
When RAM is full, the operating system moves data from RAM to a location on secondary storage called virtual memory. The data is swapped back to RAM if needed. Virtual memory is simply an area of secondary storage that is used like RAM. It is temporary storage located on the hard disk
Define primary storage
Primary storage refers to the memory that is directly accessed by the CPU e.g. ROM, RAM, cache, registers.
Define secondary storage
Secondary storage is non-volatile. It is where all data (the operating system, applications and user files) are stored when not in use.
Define solid state storage
Solid-state drives (SSDs) are storage devices with no moving parts. SSDs have fast read/ write speeds. E.g. SSD internal/external drive, USB stick, SD card.
Define optical storage
Optical storage includes CDs, DVDs and Blu-ray. Optical Storage is very cheap per GB and is very portable.
Define magnetic storage
Magnetic storage includes hard drives and magnetic tape. Both of these have a large storage capacity and have a low cost per GB.
Define capacity
The amount of data that can be stored on the device.
Define reliability
The shelflife of the media. How long it will retain data so that it can be accessed reliably, and without error in the format in which it was originally saved.
Define speed
How quickly can the data be accessed from or written to the media.
Define portability
Can the media be easily moved about? This depends on both the size and weight of the media.
Define cost
How expensive the media is in terms of cost per gigabyte of storage.
Define durability
How resistant the media is to damage; whether it is rugged enough to survive knocks, scratches, etc.
Define bit
A single binary digit (one or zero).
Define nibble
Four bits or half a byte.
Define byte
Eight bits. A byte is enough to hold one typed character, e.g. B.
Define kilobyte
1000 bytes. About two pages of text.
Define Megabyte
1000 kB. One minute of MP3 audio equals 1MB. A high-quality digital image equals 2MB.
Define gigabyte
1000 MB. A DVD movie equals 4 to 8 GB.
Define terabyte
1000 GB. 1TB equals 250,000 photos. 1TB equals 250 films.
Define petabyte
1000 TB. 1PB equals 11,000 movies. One PB equals storing 4000 photos per day over an entire lifetime.
Define denary
In our standard number system, we have 10 digits: 0 1 2 3 4 5 6 7 8 9 This is called denary, decimal or base 10.
Define binary
Binary only uses two different digits zero and one. Computers use this system as computers are made up of switches which can be on or off.
Define overflow
During binary arithmetic, you could get a result that requires more bits than the CPU is expecting – this is called overflow.
Define binary shift
A binary shift moves every bit in a binary number left or right a certain number of places. Gaps at the beginning or end of a number are filled with zeros.
Define hexadecimal
Hexadecimal (or base 16) uses 16 different digits: 0 1 2 3 4 5 6 7 8 9 A B C D E F. Large numbers can be written, simply using hex instead of binary.
Define alphanumeric characters
Alphanumeric characters are used to make words and strings. They include uppercase and lowercase letters, the digit 0 to 9, and symbols like: ? £ and +.
Define character set
Character sets of collections of characters that are computer recognises from their binary representation.
Define ASCII/ Extended ASCII
ASCII is the most commonly used character set in the English-speaking world. ASCII uses seven bits whereas extended ASCII uses eight bits. 2 to the power of seven equals 128, 2 to the power of eight equals 256.
Define Unicode
Unicode uses 16-bit. It aims to cover every possible character or symbol in all major languages. With 16 bits we can have: 2 to the power of 16 equals 65,536 different characters.
Define pixel
Pixel is the smallest identifiable area of an image. Each pixel has a single colour and is given a binary value which represents that colour.
Colour depth
Colour depth is the number of pets used for each pixel. E.g. two bits = four colours, three bits = eight colours, four bits = 16 colours.
Define resolution
Resolution is the number of pixels in the image. It is often given as width times height.
Define metadata
Meta data is the information stored in an image file about the picture. E.g. file format, height, width, colour depth, resolution.
Define analogue
Sound is recorded by microphone as an analogue signal. Analogue signals are pieces of continually changing data.
Define digital
Analogue signals need to be converted into digital data so that computers can read in stores and files.
Define hertz
Frequency is measured in hertz. A frequency of 1Hertz means that something happens once every second.
Define sound sampling
The process of converting an analogue signal into a digital signal is called sound sampling. The amplitude of a wave is sampled at regular intervals.
Define sample rate/ sampling frequency
This is how many samples you are taking a second. It is measured in Hz.
A common sample rate is 44,100 samples per second, which is 44,100 Hz or 44.1 kHz.
Define bit depth
Bit depth is the number of bits available for each sample. E.g. CD quality sound uses 16 bits per sample 2 to the power of 16 equals 65,536 values. DVDs use 24 bits 2 to the power of 24 equals 16 million.
Define file size (sound)
File size (in bits) = sample rate (in Hz) x bit depth x duration (in seconds).
Define data compression
Data compression is the process where we make files smaller. We try to make the compressed file as close to the original as possible.
Define lossy compression
Lossy compression removes data from the file. This reduces the number of bits in the file so the file size is lower. The file cannot be returned to the original.
Define lossless compression
Lossless compression uses an algorithm to find groups of repeating data. When data is uncompressed, it is restored exactly as it was in the original.
What is optical storage?
A laser light creates marks in a pattern on the disk. A laser light detects where the marks are and then translates them into a readable format.
What is magnetic storage?
Read/ write move across the medium and change how magnetised that part of the medium is. E.g one level of magnetism will be a 1, a second will be 0.
What is solid state storage?
This is made of microchips (switches). The state of the switches will determine if a 1 or 0 is stored.
What are examples of magnetic storage?
Hard disk drive, Magnetic tape
What are examples of optical storage?
Blu-Ray, DVD-ROM, CD-ROM
What are examples of solid state storage devices?
Solid State Drive, SD Card, USB memory stick
Define capacity
How much data can it store?
Define speed
How fast can it access the data?
Define portability
How easy is it to move it from one place to another?
Define durability
How well does it last drops etc?
Define reliability
How consistently does it perform?
Define cost
How much does it cost per KB, MB or GB
What are the characteristics of optical storage?
Low capacity, low speed, relatively portable, relatively durable, not very reliable, relatively cheap
What are the characteristics of magnetic storage?
High capacity, relatively fast, not very portable, not very durable, fairly reliable, very cheap
What are characteristics of solid state storage?
Relatively high capacity, very fast, very portable, very durable, very reliable, expensive
What is a bit?
A bit is a binary digit, 0 or 1, which is the smallest unit of data a computer can store
What are common file sizes?
Keyboard characters take up 1B
Document file sizes are in kB
Storage space on a CD in MB
3,000 books or 1/4 of a movie or drive size is 1GB
300 hours of video or 1,000 copies of the Encyclopaedia in 1TB
2,000 years worth of song, 315 million photos in 1PB
How do you calculate size of text files?
1 byte per character + 10% for any overheads
How do you calculate file size of an image?
Number of pixels * number of bytes per pixel
+10% for overheads
How do you calculate sound file size?
Bytes per sample * samples per second * channels * duration
How many characters can ASCII store?
256
How many characters can Unicode store?
65,536
What is compression?
Data compression is the process of encoding data so that it needs fewer bits or bytes to represent it. Compression is useful because it helps reduce the consumption of expensive resources such as hard disk space or transmission bandwidth over the internet. On the downside, compressed data must be decompressed to be used and this extra processing may be detrimental to some applications.
What is lossless compression?
Lossless compression can compress data files without losing any of the information. It is reversible and the original data can be reconstructed. However not all files can use lossless compression.
What is lossy compression?
Loses some information when compressed, some loss is acceptable e.g sound quality. Can produce smaller files. Not good for text files where 100% accuracy is required.
Why is hex useful?
Binary produces long strings so hex is a lot shorter and easier to work with. Hex is less susceptible to error and hex can easily be converted to or from binary.
What is a bitmap image?
The page is divided into an invisible grid, and each pixel is assigned a colour.
What is a vector image?
Drawn by following a set of mathematical instructions and can be scaled infinitely without any loss in quality. Every line and shape has a value.
What is metadata?
Certain data must be defined for a bitmap image e.g height and width. Metadata describes the structure of the data file and is usually located right at the start of the file.
What is resolution?
The number of pixels used per specific area.
What is colour depth?
The number of pixels that will be used to store the colour for each pixel in a grid. 2 but gives 2 to the power of 2 (4) colours. The greater the colour depth the more data needs to be stored and the larger the file size but the more detailed the colour.
How many bits needed for real life colour?
15 or 16 bits. 24 bit true colour gives over 16.7 million colours
What is digital audio?
Sound exists as waves, but computers only understand binary values. Sound created on a computer exist as digital information that is encoded as audio files. Digital sound can be broken down into thousands of samples per second.
The quality of the samples depends on sample frequency, sample size and bit depth.
What is sample rate?
The number of audio samples captured every second
What is sample size or bit depth?
Number of bits available to store each sample
What is sample rate measured in?
Hertz
What does each sample represent?
The amplitude of the digital signal at a specific point. This is stored as an integer or a float number and encoded as binary.
How do you calculate bit rate?
Bit rate is how many bits are processed per second.
Bit rate = frequency x bit depth x channels
Odd vs even binary numbers
Odd binary numbers will end in 1, even binary numbers will end in 0
What is 0+1 in binary?
1
What is 0+0 in binary?
0
What is 1 + 1 in binary?
0 carry 1
What is 1+1+1 in binary?
1 carry 1
Define EEPROM
Electronically Erasable Programmable Read Only Memory
Instructions can be electronically erased and replaced
