Central Processing UnitPart II Bayram Güzer
Data Representation: On/Off • Computers are known as complex machines but the reality is they only know two things • ON (electricity turned on) • OFF (electricity turned off) • The two-state on/off system is called as binary system.
Data Representation: On/Off • Each 0 or 1 in the binary system is called a bit (binary digit) • The bit is the basic unit for storing data in computer memory. • Since single bits by themselves cannot store all the numbers, letters, and special characters, a computer must process the bits together in a group called as byte. • There are 8 bits in a byte.
Data Representation: On/Off • Each byte usually represents one character of data • A letter, digit or special character. • There are 8 bits in a byte. • Capacity of memory and storage are expressed in term of the number of bytes data they can hold.
Data Representation: On/Off • When number of bytes come together, they are expressed as kilobytes. • It is abbreviated as KB or K. • 1 kilobyte is equal to 1024 bytes. • Ex; Old PC memories. • A computer word, is defined as the number of bits that constitute a common unit of data, as defined by the computer system. • 32 or 64 bits for most personal computers today.
Data Representation: On/Off • When number of kilobytes come together, they are expressed as megabytes. • It is abbreviated as MB which also means 1 million bytes. • 1 megabyte is equal to 1024 KB. • Ex; Diskette, cd-rom or etc… • When number of megabytes come together, they are expressed as gigabytes. • It is abbreviated as GB which also means 1 billions of bytes. • 1 gigabyte is equal to 1024 megabytes. • Ex; Hard disks
Data Representation: On/Off • B: Byte b: bit • KB: Kilobyte - Kb: Kilobit • MB: Megabyte - Mb: Megabit • GB: Gigabyte - Gb: Gigabit • 1 B = 8 b (bit) • 1 KB = 1024 B • 1 MB = 1024 KB • 1 GB = 1024 MB
Data Representation: On/Off • 1024 KBps --- 1024 Kbps (128 KBps) • 2048 KBps --- 2048 Kbps (256 KBps) • 4096 KBps --- 4096 Kbps (512 KBps)
Data Representation: On/Off • It is known that a collection of bits can represent a character of data • But, what particular set of bits is equivalent to which character? • There must be an agreement on which groups of bits represent which characters. • ASCII • EBCDIC • Unicode
Data Representation: On/Off • The code called ASCII, which stands for American Standard Code for Information Interchange uses 7-bit for each character which is equivalent to 128 unique combinations. • A more common version is ASCII-8 which is also called as extended ASCII which can represent 256 different characters. • ASCII representation has been accepted as universal character representation in computing systems.
Data Representation: On/Off • EBCDIC stands for Extended Binary Coded Decimal Interchange Code • It is used primarily on IBM and IBM-compatible mainframes • Unicode is designed to accommodate alphabets of more than 256 characters • Uses 16 bits to represent one character • 65,536 possible values (216) • Requires twice as much space to store data
References • Capron, H. L. (2000). Computers Tools for an Information Age.(6th ed.). New Jersey, USA: Prentice Hall. • http://homepage.cs.uri.edu/faculty/wolfe/book/Readings/Reading04.htm • http://en.wikipedia.org/wiki/Pulse_%28signal_processing%29 • http://www.yale.edu/pclt/PCHW/clockidea.htm • http://www.camiresearch.com/Data_Com_Basics/data_com_tutorial.html • http://en.wikipedia.org/w/index.php?title=Relational_operator • http://en.wikipedia.org/wiki/Word_(computing) • http://en.wikipedia.org/wiki/32-bit • http://tldp.org/HOWTO/Unix-and-Internet-Fundamentals-HOWTO/core-formats.html