Computer Systems Chapter 1 Pages

Hardware-physical pieces Key hardware components in a computer system: The physical parts. – Central processing unit – executes – Input/output devices – Main memory-holds software while being processed by CPU – Secondary memory devices-Stores software until deleted from system

Software Two types: System software and applications. Software is the actually programs we will run on the computer. System programs – Operating System – Provides user interface (GUI) – Manages computer resources Application – programs designed for purpose: education, financial, medical games.

Digital Information A computer stores information digitally as binary numbers. – numbers – text – graphics and images – video – audio – program instructions In some way, all information is digitized - broken down into pieces and represented as numbers

Binary Numbers Binary number system has only two digits – 0 and 1. A single binary digit (0 or 1) is called a bit A single bit can represent two possible states, like a light bulb that is either on (1) or off (0) These combinations of bits make up letters, symbols, numbers. Binary is Base 2 number system so t here are 2 N permutations of N bits

6 Bit Permutations Therefore, N bits are needed to represent 2 N unique items 2 1 = 2 items 2 2 = 4 items 2 3 = 8 items 2 4 = 16 items 2 5 = 32 items 1 bit ? 2 bits ? 3 bits ? 4 bits ? 5 bits ? 6 bits ? 7 bits ? 8 bits ? How many items can be represented by 2 6 = 64 items 2 7 = 128 items 2 8 = 256 items

7 Bit Permutations 1 bit bits bits bits Each additional bit doubles the number of possible permutations All the different combinations possible of 0s or 1s. Question: 3 bits can represent how much data ?

Convert from decimal to binary To convert from decimal to binary use the greedy algorithm. Start with the first power of two less than or equal to the decimal number and turn that bit to 1. Then subtract the power of two from the decimal number and continue until done 256 (2 8 ) 1 ( = 60) 128 (2 7 ) 0 64 (2 6 ) 0 32 (2 5 ) 1 (60-32 = 28) 16 (2 4 ) 1 (28-16 = 12) 8 (2 3 ) 1 (12-8 = 4) 4 (2 2 ) 1 (4-4 = 0) 2 (2 1 ) 0 1 (2 0 ) is Bits in computer memory are organized into bytes. Each byte has 8 bits. The first 8 values in powers of 2 are 1, 2, 4, 8, 16, 32, 64, 128. So you can store the values 0 to 255 in 1 byte (8 bits). Base 2 number system chart

Convert from binary to decimal The decimal value of a binary number can be calculated by multiplying the digit by the value of each place and adding the results for each digit (1)(2 8 ) + (1) (2 5 ) + (1)(2 4 ) + (1)(2 3 ) + (1)(2 2 ) + (0)(2 1 ) + (0)(2 0 ) = 316

10 Storage Capacity Every memory device has a storage capacity, indicating the number of bytes it can hold Capacities are expressed in various units : KB2 10 = 1024 MB2 20 (over 1 million) GB2 30 (over 1 billion) TB2 40 (over 1 trillion) UnitSymbolNumber of Bytes kilobyte megabyte gigabyte terabyte