Chapter 4 Computer Hardware

1. Chapter 4Computer Hardware Information Technology in Theory By Pelin Aksoy and Laura DeNardis

2. Objectives • Identify some important historical milestones in the development of computers • Understand logic gates and how computers use them to process information • Identify the fundamental components of a computer • Understand how computer performance depends on factors such as processor speed, chip set, bus width, bus speed, number of CPUs, and instruction set Information Technology in Theory

3. Objectives (continued) • Examine future trends in computing and societal issues related to these advances • Understand the physical principles of data storage and the difference between mechanical, magnetic, optical, and electronic storage Information Technology in Theory

4. A Brief History of Computers • Computing devices trace back at least to the Abacus • Mechanical calculation tools in the 1600s included William Oughtred’s slide rule, BlaisePascal’s arithmetic machine, and Leibniz’s step reckoner • Calculation tools of the 1800s included Charles Babbage’s Difference and Analytical engines • Augusta Ada Byron, the Countess of Lovelace, worked with Babbage in programming the analytical engine • Herman Hollerith developed the tabulating machine to tabulate the 1890 US census data using punch cards Information Technology in Theory

5. A Brief History of Computers (continued) • The punch card concept is attributed to Joseph Marie Jacquard • The 1940s spurred big advancements in computing • John Vincent Atanasoff and Clifford Berry at the Iowa State College built the ABC • Konrad Zuse built the Z3 • Howard Aiken built the Mark I, which was programmed by Grace Murray Hopper • British scientists built the Colossus • John Mauchly and J. Presper Eckert built the ENIAC Information Technology in Theory

6. A Brief History of Computers (continued) • The transistor and integrated circuit enable smaller computers compared to vacuum tubes • Popular Electronics ran a feature story about a home “do-it-yourself” computer kit called the Altair • Radio Shack began to sell the TRS-80 home computer, and Apple Computer Inc. introduced its own line of home computers • These advances, and the introduction of IBM’s personal computer (PC) in 1981, contributed to the explosion of computers in all facets of modern life Information Technology in Theory

7. A Brief History of Computers (continued) • A variety of social and economic factors, along with advances in microprocessors and distributed networks, led to the introduction of mobile, wireless, and handheld computers Information Technology in Theory

8. Digital Logic • A computer has one or more main chips called the microprocessor, which performs most of the processing, and several other supporting chips • Integrated circuits such as microprocessors are built by combining transistors together to create logic gates • These basic building blocks can be combined to create successively larger building blocks, which may subsequently be combined to create complex circuitry and packaged with other components within a carrier to create integrated circuits such as microprocessors Information Technology in Theory

9. Digital Logic (continued) Information Technology in Theory

10. Digital Logic (continued) • Integrated circuits are built using the following types of logic gates • The difference between these logic gates is essentially the way the transistors within them are connected to each other • NOT gate (inverter) • AND gate • NAND (not AND) gate • OR gate • NOR (not OR) gate • Exclusive OR (XOR) gate • XNOR (exclusive NOR) gate Information Technology in Theory

11. Digital Logic (continued) Information Technology in Theory

12. Digital Logic (continued) Information Technology in Theory

13. Digital Logic (continued) Combining log gates to create a 1-bit binary adder Information Technology in Theory

14. Digital Logic (continued) Information Technology in Theory

15. Fundamental Components of a Computer Information Technology in Theory

16. Fundamental Components of a Computer (continued) • Computer hardware is any physical device associated with a computer, such as a keyboard or monitor • Besides the instructions that users issue through input hardware devices, computers also receive instructions via the software stored in its memory • Software is traditionally defined as a series of instructions written by computer programmers in a language that people can understand and that the computer can translate into binary • The computer must interpret and then execute each software instruction, again through the use of its transistors Information Technology in Theory

17. Input/Output Devices • Input and output devices are hardware components that interface a computer to the outside world • Examples of input devices include: • Mice • Trackballs • Microphones • Web cams • Styluses • Touch pads • Pointing sticks • Joysticks • Scanners Information Technology in Theory

18. Input/Output Devices (continued) • Examples of output devices include: • Printers • Plotters • Speakers • Projectors • Some I/O devices, such as keyboards and monitors, are integral parts of computers • However, note that not all computers have input and output devices connected to them • For example, some computers can interface to a user over a network and do not need their own I/O equipment Information Technology in Theory

19. Central Processing Unit • The most crucial component of any computer is a chip called the microprocessor or central processing unit (CPU) • The microprocessor controls the major functionality of the computer and is often called the “brains” of the computer • The microprocessor’s many tasks include fetching a wealth of software instructions, interpreting and executing these instructions, and storing and outputting results Information Technology in Theory

20. Central Processing Unit (continued) Information Technology in Theory

21. Central Processing Unit (continued) • Key component of the CPU is the control unit, where instructions are interpreted and control signals are generated • Based on the result of the interpretation, the control unit supplies crucial control signals to other parts of the computer • If the instruction involves the addition of two numbers, then the control unit issues control signals to a unit called the ALU, which is responsible for arithmetic and logical operations Information Technology in Theory

22. Central Processing Unit (continued) • The registers within the CPU are small areas for temporarily storing information, such as instructions that are supplied to the control unit and the results of addition and comparison operations implemented by the ALU • Software instructions that the CPU interprets and data that it processes are fetched from a module called main memory that resides outside the CPU • Unlike main memory, cache memory is internal to the CPU Information Technology in Theory

23. Central Processing Unit (continued) • Cache memory holds frequently used instructions and data • Because some software instructions and data are needed more often than others by the CPU, they can be stored inside the cache memory and retrieved when necessary instead of having to be fetched from the distant main memory every time they are needed • Saving frequently used instructions and data in close proximity saves considerable time and energy Information Technology in Theory

24. Main Memory • Main memory of a computer consists of two types of memory: random access memory (RAM) and read-only memory (ROM) • RAM is much more prominent; it retains its contents as long as power is supplied to the computer and loses its contents when the power is switched off • RAM is also called temporary memory or volatile memory • ROM, on the other hand, retains its contents even after power to the computer Information Technology in Theory

25. Main Memory (continued) • Essentially, two types of RAM are used to store information as long as power is supplied to the computer: static RAM (SRAM) and dynamic RAM (DRAM) • The contents of dynamic RAM must be refreshed several times per second, because the electrical charges representing the bits of DRAM leak out and must be replenished • There is no need to refresh the contents of SRAM • DRAMs include transistors and other electronic components called capacitors that store electricity, whereas SRAMs are based on transistors Information Technology in Theory

26. Main Memory (continued) • Although capacitors can store electricity, they cannot do so indefinitely • Electricity eventually leaks out of them, which is why it is necessary to refresh the contents of DRAM • Memory chips that correspond to the main memory are mostly DRAM • Cache memory within the CPU is typically SRAM • Due to fundamental differences in how the two types of RAM are constructed, they differ in speed, size, and cost Information Technology in Theory

27. Main Memory (continued) • It is faster to save and retrieve the contents of SRAM, but SRAM is also more expensive and larger than DRAM • Because cache memory has to be fast, it is better to use SRAM to build cache memory • DRAM is used within the main memory because it is the main holding area of the computer and must have a large holding capacity • Main memory also must be cheap to minimize the cost of the computer Information Technology in Theory

28. Main Memory (continued) • RAM chips retain ones and zeros that correspond to instructions and data within small areas called cells • Each RAM cell can hold one bit of information, regardless of whether it is DRAM or SRAM • Cells within RAM chips are arranged in rows and columns • Saving information to RAM is referred to as “writing to RAM,” and retrieving RAM contents is called “reading the RAM” • Information is written to and read from the RAM by addressing the RAM cells using addresses Information Technology in Theory

29. Main Memory (continued) Information Technology in Theory

30. Main Memory (continued) Information Technology in Theory

31. Main Memory (continued) • Although a major part of the instructions that the computer executes are supplied from RAM, the computer also relies on some operations based on instructions stored in ROM chips • ROM chips and RAM chips physically reside at different places within a computer, but together they constitute the main memory of the computer • The BIOS chip is an example of a ROM chip found inside a computer Information Technology in Theory

32. Main Memory (continued) • The major variations of ROMs have historically included the following: • Programmable ROM (PROM) • Erasable programmable ROM (EPROM) • Electrically erasable programmable ROM (EEPROM) • A device that is similar to EEPROM is flash memory Information Technology in Theory

33. Storage • Storage and retrieval of digital information is one of the most critical components of an IT system • Without storage, we would have no Web servers, electronic banking, e-mail, or almost any other digital application • Storage technologies are discussed later in the chapter Information Technology in Theory

34. Interconnection System • The physical system that connects I/O devices, main memory, CPU, storage, and other components is called the interconnection system • This system is actually a set of wires; they are often grouped together as a set of parallel wires that transfer signals corresponding to data, instructions, and control information in an arrangement called a parallel bus • Some connections do not rely on a set of parallel wires • Instead, they use a main connection that transfers bits one after the other, or serially, from one point to another • Such connections are called a serial bus Information Technology in Theory

35. Interconnection System (continued) Information Technology in Theory

36. Interconnection System (continued) • The number of parallel lines within a parallel bus and the transfer speed of bits across each line dictate how many overall bits the bus can carry • The larger the bus width, the quicker the bits can reach their destination; an example would be the delivery of bits from the main memory to the CPU Information Technology in Theory

37. Interconnection System (continued) • Types of computer buses include the following: • System bus—A parallel bus that connects the CPU and main memory; the system bus is also called the front side bus • Peripheral Component Interconnect (PCI) bus and PCI Express (PCI-E) bus—The PCI bus and its newer and faster version, PCI-E bus, connect expansion cards such as network interface cards and sound cards/adapters • Accelerated Graphics Port (AGP) bus—This bus connects expansion cards called graphics cards/adapters to the CPU; this circuitry supports computer graphics capabilities Information Technology in Theory

38. Interconnection System (continued) • Expansion cards are connected to the CPU by buses • They are attached to the buses by being plugged into special components called expansion slots on the computer’s motherboard Information Technology in Theory

39. Factors That Affect Computer Performance • Some of the key factors that affect computer performance are shown in the following list: • Word length • Bus width and bus speed • Memory size and memory access speed • Processor speed • Instruction set • Number of CPUs • Chip set Information Technology in Theory

40. Word Length • Word length is expressed in terms of bits and corresponds to the maximum number of bits of information that a computer can process at one time • The larger the word length is, the faster the computer • Engineers are constantly striving to design computers with larger word lengths to achieve high performance Information Technology in Theory

41. Word Length (continued) Information Technology in Theory

42. Bus Width and Bus Speed • Another factor that affects performance is the bus size, or parallel bus width • Like word length, bus size is measured in terms of bits • A computer with a large bus width can carry more bits at a time between computer components, such as between main memory and the CPU, making it faster than a computer with a small bus width • Because the buses carry important instructions, data, addresses, and control signals, the speed you can gain by using a larger bus width is important Information Technology in Theory

43. Bus Width and Bus Speed (continued) • The bus size determines how many physical wires are constructed within the bus • The more wires that designers can incorporate within a bus, the larger the bus width becomes, meaning that the bus can carry more bits at one time • Bus speed, which is measured in hertz (Hz), also affects computing performance • Even if large bus widths can enable large number of bits to move between computer components in parallel, each bus line must also carry bits as quickly as possible Information Technology in Theory

44. Memory Size and Memory Access Speed • Computers need large amounts of memory for high performance and multitasking • Because every program occupies some amount of space in RAM, a large amount of RAM is essential to operate with multiple programs • Furthermore, RAM size significantly affects computer speed because information is frequently written to and erased from RAM • If there is insufficient RAM space, the computer must frequently resort to using its hard disk, which results in diminished performance Information Technology in Theory

45. Memory Size and Memory Access Speed (continued) • Other than RAM, the size of the cache memory (expressed in bytes) is also a consideration • The more cache memory the CPU has, the better the CPU performs • The speed at which RAM and cache memory contents are written and retrieved helps to determine performance • The higher the read/write speed, the faster the computer is • Typical RAM access speeds are on the order of nanoseconds (ns), or billionths of a second Information Technology in Theory

46. Processor Speed • The on and off switching of transistors within the integrated circuits of a computer is managed by a central digital electrical signal called a clock • Computer clock speeds are measured in frequency units called hertz • Just as multipliers are used in the IT world to express large numbers of bits, multipliers are used to express large frequency values: • 1 kHz = 1000 Hz • 1 MHz = 1,000,000 Hz • 1 GHz = 1,000,000,000 Hz Information Technology in Theory

47. Processor Speed (continued) • The higher the clock frequency, the faster the computer usually is • Typical clock frequencies for modern computers range from hundreds of megahertz to a few gigahertz Information Technology in Theory

48. Processor Speed (continued) Information Technology in Theory

49. Instruction Set • A computer’s CPU is typically based on a complex instruction set computer (CISC) architecture or a reduced instruction set computer (RISC) architecture • The difference between them is the number of clock cycles it takes to execute a single instruction • Some computer architectures require more cycles to execute the same instruction than others Information Technology in Theory

50. Number of CPUs • Incorporating more than one microprocessor increases a computer’s processing power and speed because it can use more transistors and perform multitasking • Some computers have dual-core processors and quad-core processors • Besides multicore computers, multiprocessor computers are also available Information Technology in Theory