Data Representation

• The basic building block in all computers is the binary number system, which consists of 1s and 0s.
• Computers contain millions and millions of tiny 'switches', which must be in the ON or OFF position, and can be represented by the binary system.
• A switch in the ON position is represented by 1; a switch in the OFF position is represented by 0.
• Computer scientists find hexadecimal to be more convenient to use than binary as one hex digit represents four binary digits.
• The hex number is far easier for humans to remember, copy and work with.
• Error codes are often shown as hexadecimal values, referring to the memory location of the error and are usually automatically generated by the computer.
• Media Access Control (MAC) address refers to a number which uniquely identifies a device on a network, and is rarely changed so that a particular device can always be identified no matter where it is.
• A MAC address is usually made up of 48 bits which are shown as 6 groups of two hexadecimal digits.
• Each device connected to a network is given an address known as the Internet Protocol (IP) address.
• An IPv4 address is a 32-bit number written in denary or hexadecimal form
• IPv4 has recently been improved upon by the adoption of IPv6.
• An IPv6 address is a 128-bit number broken down into 16-bit chunks, represented by a hexadecimal number.
• HyperText Mark-up Language (HTML) is used when writing and developing web pages, and isn't a programming language but is simply a mark-up language.
• HTML uses <tags> which are used to bracket a piece of text for example, <h1> and </h1> surround a top-level heading.
• Computers can carry out a logical shift on a sequence of binary numbers, moving the binary number to the left or to the right.
• Each shift left is equivalent to multiplying the binary number by 2 and each shift right is equivalent to dividing the binary number by 2.
• As bits are shifted, any empty positions are replaced with a zero.
• The ASCII code system was set up in 1963 for use in communication systems and computer systems.
• A newer version of ASCII was published in 1986.
• The standard ASCII code character set consists of 7-bit codes (0 to 127 in denary or 00 to 7F in hexadecimal) that represent the letters, numbers and characters found on a standard keyboard, together with 32 control codes (that use codes 0 to 31 (denary) or 00 to 19 (hexadecimal).
• Extended ASCII uses 8-bit codes (0 to 255 in denary or 0 to FF in hexadecimal).
• Extended ASCII gives another 128 codes to allow for characters in non-English alphabets and for some graphical characters to be included.
• The main disadvantage of the ASCII code system is that it does not represent characters in non-Western languages, for example Chinese characters.
• Unicode can represent all languages of the world, thus supporting many operating systems, search engines and internet browsers used globally.
• There is overlap with standard ASCII code, since the first 128 (English) characters are the same, but Unicode can support several thousand different characters in total.
• Unicode uses one byte to represent a character, whereas Unicode will support up to four bytes per character.
• The Unicode consortium was set up in 1991.
• Version 1.0 of Unicode was published with five goals; these were to: create a universal standard that covered all languages and all writing systems, produce a more efficient coding system than ASCII, adopt uniform encoding where each character is encoded as 16-bit or 32-bit code, create unambiguous encoding where each 16-bit and 32-bit value always represents the same character, and reserve part of the code for private use to enable a user to assign codes for their own characters and symbols.
• The amplitude of a sound wave specifies its loudness.
• Sound waves vary continuously, making sound an analogue phenomenon.
• Computers cannot work with analogue data, hence sound waves need to be sampled in order to be stored in a computer.
• Sampling means measuring the amplitude of the sound wave using an analogue to digital converter (ADC).
• To convert the analogue data to digital, the sound waves are sampled at regular time intervals.
• The amplitude of the sound cannot be measured precisely, hence approximate values are stored.
• The number of bits per sample is known as the sampling resolution (also known as the bit depth).
• Sampling rate is the number of sound samples taken per second, measured in hertz (Hz), where 1Hz means ‘one sample per second’.
• The process of sampling a sound wave involves determining the amplitude of the sound wave at set time intervals (the sampling rate), which gives an approximate representation of the sound wave.
• Each sample of the sound wave is then encoded as a series of binary digits.
• Using a higher sampling rate or larger resolution will result in a more faithful representation of the original sound source.
• The higher the sampling rate and/or sampling resolution, the greater the file size.