Cisco Networking Academy Program CCNA 1 and 2 Companion Guide, Revised part 6 is the Cisco approved textbook to use alongside version of the Cisco Networking Academy Program CCNA 1 and CCNA 2 web-based courses. The topics covered provide you with the necessary knowledge to begin your preparation for the CCNA certification exam (640-801, or 640-821 and 640-811) and to enter the field of network administration. | B Page 19 Tuesday May 20 2003 2 53 PM Bits Bytes and Measurement Terms 19 Binary Representation of Data Computers are electromechanical devices made up of electronic switches. At the lowest levels of computation computers depend on these electronic switches to make decisions. As such computers react only to electrical impulses. These impulses are understood by the computer as either on or off states 1s or 0s . Computers work with and store data using electronic switches that are either on or off. Computers can only understand and use data that is in this two-state binary format. 1 represents an on state and 0 represents an off state. These 1s and 0s represent the two possible states of an electronic component in a computer. These 1s and 0s are called binary digits or bits. The American Standard Code for Information Interchange ASCII the most commonly used code for representing alphanumeric data in a computer uses binary digits to represent the symbols typed on the keyboard. When computers send on off states over a network electricity light or radio waves represent the 1s and 0s. Each character has a unique pattern of eight binary digits assigned to represent the character. Bits Bytes and Measurement Terms Bits are binary digits. They are either 0s or 1s. In a computer they are represented by on off switches or the presence or absence of electrical charges light pulses or radio waves. For example A binary 0 might be represented by 0 volts of electricity 0 0 volts . A binary 1 might be represented by 5 volts of electricity 1 5 volts . Computers are designed to use groupings of 8 bits. This grouping of 8 bits is called a byte. In a computer 1 byte represents a single addressable storage location. These storage locations represent a value or a single character of data such as an ASCII code. The total number of combinations of the eight switches being turned on and off is 256 or 28 . The value range of a byte is from 0 to 255. So a byte is an important concept
