# Computing-Chapter 4

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Describe the different units (relative to bytes).
1 byte = 8 bits. 1024 bytes = 1 kilobyte. 1024 kilobytes = 1 megabyte. 1024 megabytes = 1 gigabyte. 1024 gigabytes = 1 terabyte. 4 bits (half a byte) = a nibble. Bit,B, KB, MB, GB
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How is binary used in computers?
All data has to be converted to binary format to be processed by the computer. Modern computers work in binary as it’s easy to represent 2 states in simple electronic circuits.
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When does an overflow error occur?
When two or more binary numbers are added together and the result is incorrect as it is too large to fit into the bits allocated
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As it shorter and is therefore easier to convert
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What is a character set?
A list of all the characters that are accessible to a computer system. When a character is selected on the keyboard, a binary code for that character is input into the computer.
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The number of bits used to store the code determines how many characters or symbols can be used. Give examples.
ASCII uses 7 bits so can provide 128 character/symbols – many of these used for controlling peripherals. Unicode is a 16 bit character set, created with 65, 536 characters available however Unicode uses more storage space (more bytes per characters).
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What are digital images composed of?
Pixels (smallest element in a digital image). No. of bits used for a pixel determines how many colours each dot can represent: 1 bit represents 2 colours –black and white, 2 bits = 4 (2^2) colours, 8b = 256 (2^8)
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How are digital images stored and is resolution (b)?
As binary values, but the computer is able to convert the binary value into the image as the binary data contains metadata (gives details of image height, width + colour depth).
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What is resolution and how does it affect the size of the file? Also how does colour depth affect the file size?
Resolution is the no. of pixels per inch - more dpi (dots per inch) gives a better image resolution + increases the pixels per inch + file size. Increased colour depth = more bits use per pixel = increased file size.
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What is a bitmapped image?
If it is displayed enlarged on screen the actual image size doesn’t change, the dots just get bigger and the image becomes pixelated.
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How is sound stored?
As binary files + can be input into the computer using a microphone which use ADC (analog to digital converter) to create a digital sound signal.
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How is sound sampled before it stored in digital form?
The analog wave is sampled and a measurement is taken at regular intervals. The measurement is converted into binary data and stored in a sound file. The microphone used for input uses an ADC (Analog digital converter).
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What is the sampling rate?
The number of samples taken per second (in Hz) from the analogue input to create a digital signal. High sample rates are used are used to create quality sound reproduction but = large files + more storage needed.
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What is sampling resolution?
No. of bits used to store each sample measured in BPS (Bits per second). High resolution used for high-quality sound reproduction
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Explain how instructions are coded as bit patterns.
CPU fetches + decodes 1st instruction. CPU updates program counter to keep track of next instruction. CPU processes decoded program instruction which consists of an operator (instruction) + operand (data).
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How does the computer distinguish between instructions and data?
The operator is the first few (i.e.4) bits, operand = last 4 bits. Both in binary form +held in main memory in unique addresses so OS ensures that both are stored in expected location when program runs.
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## Other cards in this set

### Card 2

#### Front

How is binary used in computers?

#### Back

All data has to be converted to binary format to be processed by the computer. Modern computers work in binary as it’s easy to represent 2 states in simple electronic circuits.

### Card 3

#### Front

When does an overflow error occur?

### Card 5

#### Front

What is a character set?