Computer Systems Chapter 1

1. Computer SystemsChapter 1 Pages 2 - 16

2. 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

3. 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.

4. 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

5. 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 there are 2N permutations of N bits

6. 1 bit ? 2 bits ? 3 bits ? 4 bits ? 5 bits ? 6 bits ? 7 bits ? 8 bits ? How many items can be represented by Bit Permutations Therefore, N bits are needed to represent 2N unique items 21 = 2 items 22 = 4 items 23 = 8 items 24 = 16 items 25 = 32 items 26 = 64 items 27 = 128 items 28 = 256 items

7. 1 bit 2 bits 4 bits 3 bits 0 1 00 01 10 11 000 001 010 011 100 101 110 111 0000 0001 0010 0011 0100 0101 0110 0111 1000 1001 1010 1011 1100 1101 1110 1111 Bit Permutations 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? 8 23

8. 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). Convert from decimal to binary 31610 • 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 (28) 1 (316-256 = 60) 128 (27) 0 64 (26) 0 32 (25) 1 (60-32 = 28) 16 (24) 1 (28-16 = 12) 8 (23) 1 (12-8 = 4) 4 (22) 1 (4-4 = 0) 2 (21) 0 1 (20) 0 1001111002 is 31610 Base 2 number system chart

9. 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)(28) + (1) (25) + (1)(24) + (1)(23) + (1)(22) + (0)(21) + (0)(20) 256 + 32 + 16 + 8 + 4 + 0 + 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: Unit Symbol Number of Bytes KB 210 = 1024 kilobyte megabyte gigabyte terabyte MB 220 (over 1 million) GB 230 (over 1 billion) TB 240 (over 1 trillion)