How the Computer Works 1

How the Computer Works 1

Lecture Topics Functions of a computer Data versus information Bits and bytes Storage Processing How computers evolved Copyright 2011 Pearson Education, Inc. Publishing as Prentice Hall 2

Hardware and Software Hardware: The physical devices that make up a computer Computer is a system composed of several components that all work together Typical major components: Central processing unit Main memory Secondary storage devices Input and output devices

Secondary Storage Devices Secondary storage: can hold data for long periods of time Programs normally stored here and loaded to main memory when needed Types of secondary memory Disk drive: magnetically encodes data onto a spinning circular disk Solid state drive: faster than disk drive, no moving parts, stores data in solid state memory Flash memory: portable, no physical disk Optical devices: data encoded optically

Input Devices Input: data the computer collects from people and other devices Input device: component that collects the data Examples: keyboard, mouse, scanner, camera Disk drives can be considered input devices because they load programs into the main memory

Output Devices Output: data produced by the computer for other people or devices Can be text, image, audio, or bit stream Output device: formats and presents output Examples: video display, printer Disk drives and CD recorders can be considered output devices because data is sent to them to be saved

Software Everything the computer does is controlled by software General categories: Application software System software Application software: programs that make computer useful for every day tasks Examples: word processing, email, games, and Web browsers

Software (cont’d.) System software: programs that control and manage basic operations of a computer Operating system: controls operations of hardware components Utility Program: performs specific task to enhance computer operation or safeguard data Software development tools: used to create, modify, and test software programs

Random access memory (RAM): Main memory: where computer stores a program while program is running, and data used by the program Known as Random Access Memory or RAM CPU is able to quickly access data in RAM Volatile memory used for temporary storage while program is running Contents are erased when computer is off Copyright 2011 Pearson Education, Inc. Publishing as Prentice Hall 9

Main Memory Addresses Address: A “name” that uniquely identifies one cell in the computer’s main memory The names are actually numbers. These numbers are assigned consecutively starting at zero. Numbering the cells in this manner associates an order with the memory cells. 1-10

Figure 1.8 Memory cells arranged by address 1-11

Read-only memory (ROM): Stores start-up instructions Permanent storage Copyright 2011 Pearson Education, Inc. Publishing as Prentice Hall 12

Electrical Switches The system unit contains the CPU The CPU uses a large number of switches Two states: 1 or 0 (on or off) Binary language consists of two numbers: 1 or 0 These switches are used to process data Lock Copyright 2011 Pearson Education, Inc. Publishing as Prentice Hall 13

The CPU Central processing unit (CPU): the part of the computer that actually runs programs Most important component Without it, cannot run software Used to be a huge device Microprocessors: CPUs located on small chips

Central Processing Unit (CPU) Referred to as the “brains” of the computer Controls all functions of the computer Processes all commands and instructions Can perform billions of tasks per second (over 6 billion tasks per second) This is the part of the computer that actually runs programs Most important component Without it, cannot run software Used to be a huge device Microprocessors: CPUs located on small chips Copyright 2011 Pearson Education, Inc. Publishing as Prentice Hall 15

How Computers Store Data All data in a computer is stored in sequences of 0s and 1s Bit Binary digit 0 or 1 electrical component that can hold positive or negative charge, like on/off switch Byte: just enough memory to store letter or small number Divided into eight bits The on/off pattern of bits in a byte represents data stored in the byte 8 bits Each letter, number, and character is a string of eight 0s and 1s

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Storage Capacity is the number of bytes a storage medium can hold Page 354 Figure 7-2 Discovering Computers 2012: Chapter 7 18

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Storing Characters Data stored in computer must be stored as binary number Characters are converted to numeric code, numeric code stored in memory Most important coding scheme is ASCII There are 128 in the Standard ASCII character set, and there are 256characters in the Extended ASCII character set. Which is what most computers use Unicode coding scheme becoming standard Compatible with ASCII Can represent characters for other languages

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getty.txt F o u r a n d s e v e n 70 111 117 114 32 97 110 100 32 115 101 118 101 110 By looking in the ASCII table, you can see a one-to-one correspondence between each character and the ASCII code used. Note the use of 32 for a space -- 32 is the ASCII code for a space. We could expand these decimal numbers out to binary numbers (so 32 00100000) if we wanted to be technically correct -- that is how the computer really deals with things. (more on this later) The first 32 values (0 through 31) are codes for things like carriage return and line feed. The space character is the 33rd value, followed by punctuation, digits, uppercase characters and lowercase characters. Copyright 2011 Pearson Education, Inc. Publishing as Prentice Hall 22

Storing Numbers Bit represents two values, 0 and 1 Computers use binary numbering system Position of digit j is assigned the value 2j-1 To determine value of binary number sum position values of the 1s Byte size limits are 0 and 255 0 all bits off; 255 all bits on To store larger number, use several bytes

Representing Numeric Values Binary notation: Uses bits to represent a number in base two Limitations of computer representations of numeric values Overflow: occurs when a value is too big to be represented Truncation: occurs when a value cannot be represented accurately 1-24

Advanced Number Storage To store negative numbers and real numbers, computers use binary numbering and encoding schemes Negative numbers encoded using two’s complement Real numbers encoded using floating-point notation

Other Types of Data Digital: describes any device that stores data as binary numbers Digital images are composed of pixels To store images, each pixel is converted to a binary number representing the pixel’s color Digital music is composed of sections called samples To store music, each sample is converted to a binary number

Representing Images Bit map techniques Pixel: short for “picture element” RGB Luminance and chrominance Vector techniques Scalable TrueType and PostScript 1-27

Representing Sound Sampling techniques Used for high quality recordings Records actual audio MIDI Used in music synthesizers Records “musical score” 1-28

Figure 1.12 The sound wave represented by the sequence 0, 1.5, 2.0, 1.5, 2.0, 3.0, 4.0, 3.0, 0 1-29

Secondary Storage Devices Secondary storage: can hold data for long periods of time Programs normally stored here and loaded to main memory when needed Types of secondary memory Disk drive: magnetically encodes data onto a spinning circular disk Solid state drive: faster than disk drive, no moving parts, stores data in solid state memory Flash memory: portable, no physical disk Optical devices: data encoded optically Reading is the process of transferring items from a storage medium into memory Writing is the process of transferring items from memory to a storage medium

Hard Disks A hard disk contains one or more inflexible, circular platters that use magnetic particles to store data, instructions, and information The hard disk/drive is your computer’s primary device for permanent storage of software and documents. The hard drive is a nonvolatile storage device, meaning that it holds the data and instructions your computer needs permanently, even after the computer is turned off Page 355 Figure 7-5 Discovering Computers 2012: Chapter 7 31

Figure 1.9 A magnetic disk storage system 1-32

Flash Memory Storage Flash memory chips are a type of solid state media and contain no moving parts Solid state drives (SSDs) have several advantages over magnetic hard disks: Faster access time Pages 362 - 363 Faster transfer rates Generate less heat and consume less power Discovering Computers 2012: Chapter 7 Last longer 33

Cloud Storage Cloud storage is an Internet service that provides storage to computer users DropBox and Box are examples Access files from any computer Store large files instantaneously Allow others to access their files View time-critical data and images immediately Store offsite backups Provide data center functions Page 368 Figure 7-23 Discovering Computers 2012: Chapter 7 34

Optical Discs An optical disc consists of a flat, round, portable disc made of metal, plastic, and lacquer that is written and read by a laser Typically store software, data, digital photos, movies, and music Read only vs. rewritable DVD DVD-RW (rewritable DVD) Blu-Ray (5 X the storage of DVD) Page 370 Figure 7-25 Discovering Computers 2012: Chapter 7 35

More About the Processing Unit Copyright 2011 Pearson Education, Inc. Publishing as Prentice Hall 36

How a Program Works CPU designed to perform simple operations on pieces of data Examples: reading data, adding, subtracting, multiplying, and dividing numbers Understands instructions written in machine language and included in its instruction set Each brand of CPU has its own instruction set To carry out meaningful calculation, CPU must perform many operations

How a Program Works (cont’d.) Program must be copied from secondary memory to RAM each time CPU executes it CPU executes program in cycle: Fetch: read the next instruction from memory into CPU Decode: CPU decodes fetched instruction to determine which operation to perform Execute: perform the operation

How a Program Works (cont’d.) Figure 1-16 The fetch-decode-execute cycle

How a Program Works (cont’d.) Control Unit Manages switches inside the CPU Remembers Sequence of processing stages How switches are set for each stage Uses beat of system clock to move switch to correct on or off setting for each stage Copyright 2011 Pearson Education, Inc. Publishing as Prentice Hall 40

How a Program Works (cont’d.) ALU Arithmetic Logic Unit Arithmetic logic unit (ALU) performs Mathematical operations Addition Subtraction Multiplication Division Test comparisons ( , , ) Logical OR, AND, and NOT operations Copyright 2011 Pearson Education, Inc. Publishing as Prentice Hall 41

The Fetch-Execute Cycle in Detail A register is a small storage area in the CPU. The von Neumann architecture is characterized by the fact that instructions and data are logically the same and can both be stored in memory. Copyright 2011 Pearson Education, Inc. Publishing as Prentice Hall 42

Word Size A computer processor handles bits in chunks called word size— for example, a 32-bit word size transfers data within each microprocessor chip in 32-bit, or 4-byte, chunks. A computer that uses 64-bit word size is faster than a 32-bit computer. Copyright 2011 Pearson Education, Inc. Publishing as Prentice Hall 43

System Clock The clock rate typically refers to the frequency at which a CPU is running. It is measured in the unit Hertz. Moves CPU from one stage of the machine cycle to the next Acts as a metronome, keeping a steady beat or tick Ticks, known as the clock cycle, set the pace Pace, known as clock speed, is measured in hertz (Hz) Today’s system clocks are measured in gigahertz (GHz) or one billion clock ticks per second. What does it mean to say that the speed of a processor is 866 MHz? Ans: The processor cycles 866,000,000 times per second, which is related to the number of instructions it can process per unit time. Copyright 2011 Pearson Education, Inc. Publishing as Prentice Hall 44

How Computers Evolved Copyright 2011 Pearson Education, Inc. Publishing as Prentice Hall 45

Moore’s Law Gordon Moore, the cofounder of processor manufacturer Intel, predicted more than 40 years ago that the number of transistors on a processor would double every 18 months. Known as Moore’s Law, this prediction has been remarkably accurate—but only with tremendous engineering ingenuity. The first 8086 chip had only 29,000 transistors and ran at 5 MHz. Notebook computers today have 820 million transistors and run at 2.6 GHz—more than 200 times faster than its original counterpart. GlobalFoundries plans to accelerate the introduction of 14 nm (nanometer) chips in 2014, 46

Advancing Rates of Technology (Moore’s Law) 5-47

Von Neumann Architecture “stored program” serial uniprocessor design binary internal encoding CPU–Memory–I/O orgranization “fetch-decodeexecute” instruction cycle

Electrical Switches The system unit contains the CPU The CPU uses a large number of switches Two states: 1 or 0 (on or off) Binary language consists of two numbers: 1 or 0 These switches are used to process data Lock Copyright 2011 Pearson Education, Inc. Publishing as Prentice Hall 49

Early Computer Switches Vacuum tubes as switches Allow or block the flow of electrical current Take up a large amount of space Generate heat and burn out frequently Impractical due to size and reliability issues Copyright 2011 Pearson Education, Inc. Publishing as Prentice Hall 50

ENIAC noted for massive scale and redundant design decimal internal coding operational in 1946

Transistors Transistors Electrical switches built of layers of silicon Early transistors were built in separate units as small metal rods Each rod was a small on/off switch Smaller and faster than vacuum tubes Produced less heat Copyright 2011 Pearson Education, Inc. Publishing as Prentice Hall 52

Integrated Circuits Integrated circuits use solid-state technology, whereby electrons travel through solid material called silicon Made of semiconductor material, silicon Contain huge number of transistors, resistors, capacitors, and diodes Small size, only ¼ inch in diameter 53

Microprocessors Chip that contains CPU Intel 4004 First complete microprocessor on a single integrated circuit Built in 1971 Contained 2,300 transistors Current CPUs contain more than 500 million transistors Copyright 2011 Pearson Education, Inc. Publishing as Prentice Hall 54

The Death of Moore’s Law? Moore’s Law is possible because the distance between the pathways inside silicon chips gets smaller with each successive generation Since the pathways are closer together, electrons travel shorter distances If electrons travel half the distance to make a calculation, that means the chip is twice as fast This shrinking can’t go on forever Three interrelated forces—size, heat, and power—threaten to slow down Moore’s Law’s advance As chips get smaller and more powerful, they get hotter and present power-management challenges At some point Moore’s Law will stop because we will no longer be able to shrink the spaces between components on a chip. 5-55

The Death of Moore’s Law? Microsoft, Yahoo!, and Google have all built massive data centers in the Pacific Northwest in order to benefit from cheap hydroelectric power The chief eco officer at Sun Microsystems has claimed that computers draw four to five percent of the world’s power Google’s chief technology officer has said that the firm spends more to power its servers than the cost of the servers themselves Chips can’t get smaller forever because chip pathways can’t be shorter than a single molecule and actual physical limit may be higher 5-56

Buying Time Multicore microprocessors: Microprocessors with two or more (typically lower power) calculating processor cores on the same piece of silicon For many applications, the multicore chips will outperform a single speedy chip, while running cooler and drawing less power Multicore processors are now mainstream Today, most PCs and laptops sold have at least a two-core (dualcore) processor Intel has demonstrated chips with upwards of fifty cores 5-57

Buying Time Another approach moves chips from being paper-flat devices to built-up 3-D affairs By building up as well as out, firms are radically boosting speed and efficiency of chips 5-58

Nanotechnology The prefix “nano” stands for one-billionth Ability to manufacture extremely small devices “Smart” nanodust may be combined with wireless technologies to provide new environmental monitoring systems Current approach – start big and squeeze, press, slice, and dice to make things small Nanotechnology approach – start with the smallest element possible (i.e., atom) and build up This nanomechanical structure fabricated by a team of physicists at Boston University consists of a central silicon beam, 10.7 microns long and 400 nm wide, that bears a paddle-array 500 nm long and 200 nm wide along each side. This antennalike structure oscillated at 1.49 gigahertz or 1.49 billion times per second, making it the fastest moving nanostructure yet created. 59

Nanotechnology Impact Pharmaceuticals Drug delivery encapsulated in “nano-spheres” Electronics Faster, smaller processors Immense storage capacities Material Science Stronger materials Super conductivity Buckyball from Wikipedia 60

Quantum Computing Many believe that quantum computing systems represent the next major revolution in computing Quantum computers will be exponentially faster than today’s fastest supercomputers 61

Quantum Computing Video - CNN Video Quantum computing uses qubits instead of transistors (bits) A single qubit (utilizing particle spin) stores and processes twice as much information as a regular bit. Combining qubits delivers exponential improvement Two qubits are four times more powerful than two bits A 64-qubit computer would theoretically be 264 ( 18 billion trillion) times more powerful than the latest 64-bit computers! The first prototype quantum computer (with two qubits) was created in 1998 In 2001, Almaden Research Center demonstrated a 7-qubit machine (using 10 billion billion atoms) that could factor the number 15 In early February 2007, D-Wave Systems, Inc., a privately-held Canadian firm headquartered near Vancouver, announced: “the world’s first commercially viable quantum computer” 62

DNA Computers Use DNA molecules and special enzymes instead of silicon chips Because it involves the four nucleic acids represented by A, T, C, and G, it is NOT a system of binary computing. 330 trillion operations per second 100,000 times faster than current silicon-based computers No practical applications yet Copyright 2011 Pearson Education, Inc. Publishing as Prentice Hall 63