Data Representation Flashcards
What is a bit ?
A single bit is the smallest size of digital data and has only two values - zero and one.
What is a byte ?
A ‘byte’ contains 8 bits, for example 11101001 is a byte. A single keyboard character that you type, such as the letter A or the letter T takes up one byte of storage.
What is a nibble?
It is the term given to a group of four bits. Therefore two nibbles make a byte.
How many different values can a byte make?
2^{8} = 256 different values
How many different values can a nibble make?
2^{4} = 16 different values
why do we need to consider data to be most useful in binary form?
The answer, is that computers are used to process and store data - and computers can only use binary numbers.
What is an overflow?
When a binary arithemtic leads to a result the requires more bits than the CPU is expecting
What does the computer do in the case of an overflow?
Computer usually deals with these extra bits by storing them elsewhere. Overflow flags are used to show that an overflow error has occured
What is hexadecimal numbers?
Hexadecimal numbers are base-16 which uses sixteen symbols.
Why do people prefer to use hexadecimal numbers?
Hexadecimal is useful because it is much more readable to humans than binary but at the same time it still shares a lot of the qualities of binary. It is widely used in computing because it is a much shorter way of representing a byte of data. It is much more compact and user friendly than a binary number.
- Less chance of input errors because it is smaller
- Easier to convert between binary and hex than binary and denary
Uses of hexdecimal
- MAC Addresses
- HTML/CSS color codes
What is ASCII?
The system uses binary codes to represent each character, number and symbol in the chosen language.The most commonly used system is called the 7 bit standard ASCII code short for (The American Standard Code for Information Interchange). 7 bits gives you 27 possible values. This is 2 x 2 x 2 x 2 x 2 x 2 x 2, or 128. So the ASCII character set goes from 0-127.
How and why is the 7 bit system strange to the computer?
Since computer architecture is built around the byte (which has 8 bits) the 7-bit ASCII table is a little inconvenient. So ASCII characters are padded out to 8 bits, with the first bit always set to 0. This makes memory management a little easier. There is, however, an extension to ASCII, called “Extended ASCII”, that makes use of this spare digit to fit in another 128 characters commonly used in other languages.
How does the inputs from a computer work?
It can only tell them apart by the signals that are sent when a key is pushed. These signals tell the computer the position of the key on the keyboard, not what is written on it.
What happens when you press a key?
When you press a key on your keyboard the ‘character set’ translates the signal produced from the key’s position into its proper binary code value. And going the other way, the character set maps code values back into their correct symbol (glyph) for display.
What is a character set?
A character set is the mapping between characters and their identifying code values.
What is ASCII extended?
It is when it uses the whole byte (8 bits) instead of the 7 usually used
What is a font/typeface?
The font or typeface determines how those characters look, but a 3 is a 3 whether it’s in bold or italic, Times New Roman or Arial.
What is Unicode?
A very popular 2 byte (16 bit) encoding standard is called ‘Unicode’. This 2 byte scheme can represent 65,000+ characters (two to the power of 16)
Why was Unicode developed?
Unicode can handle any language and it does so by the user selecting a specific ‘code page’ which is one portion of the total unicode space. Each code page represents the chosen language.
What is extended Unicode?
A later version of Unicode uses even more bits - 21 bits - in order to include ancient languages such as Egyptian Hieroglyphics and even emojis.
Formula for calculating the file size
File size in bits = number of bits per character * Number of characters
What are the two most popular type of input devices for images?
The two most popular types of input devices for creating an image in binary form are the flatbed scanner and the digital camera.
How does a flatbed scanner work?
A physical photograph can be copied into a binary file by using a flatbed scanner. The photo is placed face down on the glass, then a scanning head slowly moves across it. The head moves into its first position, and takes a reading of all the colours it senses in a narrow strip. Then it moves slightly and takes another set of readings. This continues until the head has scanned the whole photograph.
The binary data is stored as a file. This file can then be imported into an image editing application for processing.
How does a camera work?
A digital camera has an image sensor that creates binary files directly.
These files are then stored in the camera’s memory card or transferred by USB cable and Wi-Fi into a computer.
How do you turn a real image into a digital picture?
The first step is make a grid.
We’ve overlaid the image below with a grid of lines. This divides it up into smaller sections. When an image is digitised - it is divided up into many individual elements. Only a single colour to be present within each box. With only one colour per box, you can represent each using just a single binary number.
The sections of a grid like this are called ‘pixels’ which is short for ‘picture element’. And by increasing the number of pixels and making them very small, the image looks completely smooth. (Increasing resolution)
