The computer as a machine consists of different components that interact with each other to provide the desired functionality of the computer. As a user of the computer, we need to be aware of the main components of the computer, their functions and the interconnection between the different components of the computer. This chapter describes the different hardware components of the computer.
When we talk of computer hardware, the three related terms that require introduction are—computer architecture, computer organization and computer design. Computer architecture refers to the structure and behavior of the computer. It includes the specifications of the components, for example, instruction format, instruction set and techniques for addressing memory, and how they connect to the other components. Given the components, computer organization focuses on the organizational structure. It deals with how the hardware components operate and the way they are connected to form the computer. Given the system specifications, computer design focuses on the hardware to be used and the interconnection of parts. Different kinds of computer, such as a PC or a mainframe computer may have different organization; however, basic organization of the computer remains the same.
A computer consists of three main components—(1) Input/Output (I/O) Unit, (2) Central Processing Unit (CPU), and (3) Memory Unit. The computer user interacts with the computer via the I/O unit. The purpose of I/O unit is to provide data and instructions as input to the computer and to present relevant information as output from the computer. CPU controls the operations of the computer and processes the received input to generate the relevant output. The memory unit stores the instructions and the data during the input activity, to make instructions readily available to CPU during processing. It also stores the processed output. This chapter discusses the hardware components of the computer and the interaction between them.
Central Processing Unit (CPU) or the processor is also often called the brain of computer. CPU (Figure 2.1) consists of Arithmetic Logic Unit (ALU) and Control Unit (CU). In addition, CPU also has a set of registers which are temporary storage areas for holding data, and instructions. ALU performs the arithmetic and logic operations on the data that is made available to it. CU is responsible for organizing the processing of data and instructions. CU controls and coordinates the activity of the other units of computer. CPU uses the registers to store the data, instructions during processing.
CPU executes the stored program instructions, i.e. instructions and data are stored in memory before execution. For processing, CPU gets data and instructions from the memory. It interprets the program instructions and performs the arithmetic and logic operations required for the processing of data. Then, it sends the processed data or result to the memory. CPU also acts as an administrator and is responsible for supervising operations of other parts of the computer.
The CPU is fabricated as a single Integrated Circuit (IC) chip, and is also known as the microprocessor. The microprocessor is plugged into the motherboard of the computer (Motherboard is a circuit board that has electronic circuit etched on it and connects the microprocessor with the other hardware components).
Figure 2.1 CPU
Figure 2.2 CPU registers
The function of a (CU) can be considered synonymous with that of a conductor of an orchestra. The conductor in an orchestra does not perform any work by itself but manages the orchestra and ensures that the members of orchestra work in proper coordination.
The memory unit consists of cache memory and primary memory. Primary memory or main memory of the computer is used to store the data and instructions during execution of the instructions. Random Access Memory (RAM) and Read Only Memory (ROM) are the primary memory. In addition to the main memory, there is another kind of storage device known as the secondary memory. Secondary memory is non-volatile and is used for permanent storage of data and programs. A program or data that has to be executed is brought into the RAM from the secondary memory.
Figure 2.3 Illustration of cache memory
Figure 2.4 Interaction of CPU with memory
Magnetic tape drives, disk drives and optical disk drives are the different types of storage devices.
A computer program is a set of instructions that describe the steps to be performed for carrying out a computational task. The program and the data, on which the program operates, are stored in main memory, waiting to be processed by the processor. This is also called the stored program concept.
An instruction is designed to perform a task and is an elementary operation that the processor can accomplish. An instruction is divided into groups called fields. The common fields of an instruction are— Operation (op) code and Operand code (Figure 2.5). The remainder of the instruction fields differs from one computer type to other. The operation code represents action that the processor must execute. It tells the processor what basic operations to perform. The operand code defines the parameters of the action and depends on the operation. It specifies the locations of the data or the operand on which the operation is to be performed. It can be data or a memory address.
Figure 2.5 Instruction format
Figure 2.6 Instruction format for ADD command
The number of bits in an instruction varies according to the type of data (could be between 8 and 32 bits). Figure 2.6 shows the instruction format for ADD command.
A processor has a set of instructions that it understands, called as instruction set. An instruction set or an instruction set architecture is a part of the computer architecture. It relates to programming, instructions, registers, addressing modes, memory architecture, etc. An Instruction Set is the set of all the basic operations that a processor can accomplish. Examples of some instructions are shown in Figure 2.7. The instructions in the instruction set are the language that a processor understands. All programs have to communicate with the processor using these instructions. An instruction in the instruction set involves a series of logical operations (may be thousands) that are performed to complete each task. The instruction set is embedded in the processor (hardwired), which determines the machine language for the processor. All programs written in a high-level language are compiled and translated into machine code before execution, which is understood by the processor for which the program has been coded.
Figure 2.7 Examples of some instructions
Two processors are different if they have different instruction sets. A program run on one computer may not run on another computer having a different processor. Two processors are compatible if the same machine level program can run on both the processors. Therefore, the system software is developed within the processor’s instruction set.
Microarchitecture is the processor design technique used for implementing the Instruction Set. Computers having different microarchitecture can have a common Instruction Set. Pentium and Athlon CPU chips implement the x86 instruction set, but have different internal designs.
The primary responsibility of a computer processor is to execute a sequential set of instructions that constitute a program. CPU executes each instruction in a series of steps, called instruction cycle (Figure 2.8).
Figure 2.8 Instruction cycle
Figure 2.9 Steps in instruction cycle
A CPU performance is measured by the number of instructions it executes in a second, i.e., MIPS (million instructions per second), or BIPS (billion instructions per second).
A processor’s instruction set is a determining factor in its architecture. On the basis of the instruction set, microprocessors are classified as—Reduced Instruction Set Computer (RISC), and Complex Instruction Set Computer (CISC). The x86 instruction set of the original Intel 8086 processor is of the CISC type. The PCs are based on the x86 instruction set.
Processors like Athlon XP and Pentium IV use a hybrid of both technologies.
Pipelining improves instruction execution speed by putting the execution steps into parallel. A CPU can receive a single instruction, begin executing it, and receive another instruction before it has completed the first. This allows for more instructions to be performed, about, one instruction per clock cycle.
Parallel Processing is the simultaneous execution of instructions from the same program on different processors. A program is divided into multiple processes that are handled in parallel in order to reduce execution time.
CPU sends data, instructions and information to the components inside the computer as well as to the peripherals and devices attached to it. Bus is a set of electronic signal pathways that allows information and signals to travel between components inside or outside of a computer. The different components of computer, i.e., CPU, I/O unit, and memory unit are connected with each other by a bus. The data, instructions and the signals are carried between the different components via a bus. The features and functionality of a bus are as follows—
Figure 2.10 Interaction between CPU and memory
Figure 2.11 shows interaction between processor, memory and the peripheral devices.
The functions of data bus, address bus and control bus, in the system bus, are as follows—
Figure 2.11 Interaction between CPU, memory and peripheral devices
The functions of data bus, address bus and control bus, in the expansion bus, are as follows—
The peripheral devices interact with the CPU of the computer via the bus. The connections to the bus from the peripheral devices are made via the ports and sockets provided at the sides of the computer. The different ports and sockets facilitate the connection of different devices to the computer. Some of the standard port connections available on the outer sides of the computer are— port for mouse, keyboard, monitor, network, modem, and, audio port, serial port, parallel port and USB port. The different ports are physically identifiable by their different shapes, size of contact pins and number of pins. Figure 2.12 shows the interaction of serial and parallel port interfaces with the devices.
Figure 2.12 Interaction of serial and parallel port interfaces
There are a number of factors involved that are related to the CPU and have an effect on the overall speed and performance of the computer. Some of the factors that affect the performance of the computer include—
Figure 2.13 System properties in Windows XP Professional
Figure 2.13 shows the general information about a computer as displayed in the system properties window in Windows XP Professional.
The computer cabinet encloses the components that are required for the running of the computer. The components inside a computer cabinet include the power supply, motherboard, memory chips, expansion slots, ports and interface, processor, cables and storage devices.
The computer is built up around a motherboard. The motherboard is the most important component in the PC. It is a large Printed Circuit Board (PCB), having many chips, connectors and other electronics mounted on it. The motherboard is the hub, which is used to connect all the essential components of a computer. The RAM, hard drive, disk drives and optical drives are all plugged into interfaces on the motherboard. The motherboard contains the processor, memory chips, interfaces and sockets, etc.
The motherboard may be characterized by the form factor, chipset and type of processor socket used. Form factor refers to the motherboard’s geometry, dimensions, arrangement and electrical requirements. Different standards have been developed to build motherboards, which can be used in different brands of cases. Advanced Technology Extended (ATX) is the most common design of motherboard for desktop computers. Chipset is a circuit, which controls the majority of resources (including the bus interface with the processor, cache memory and RAM, expansion cards, etc.) Chipset’s job is to coordinate data transfers between the various components of the computer (including the processor and memory). As the chipset is integrated into the motherboard, it is important to choose a motherboard, which includes a recent chipset, in order to maximize the computer’s upgradeability. The processor socket may be a rectangular connector into which the processor is mounted vertically (slot), or a square-shaped connector with many small connectors into which the processor is directly inserted (socket). The Basic Input Output System (BIOS) and Complementary Metal-Oxide Semiconductor (CMOS) are present on the motherboard.
Figure 2.14 ROM BIOS
Figure 2.15 Battery for CMOS chip
Motherboard has a certain number of I/O sockets that are connected to the ports and interfaces found on the rear side of a computer (Figure 2.16). You can connect external devices to the ports and interfaces, which get connected to the computer’s motherboard.
Figure 2.16 Ports on the rear side of a PC
The expansion slots (Figure 2.17) are located on the motherboard. The expansion cards are inserted in the expansion slots. These cards give the computer new features or increased performance. There are several types of slots:
Figure 2.17 Expansion slots
Ribbon cables (Figure 2.18) are flat, insulated and consist of several tiny wires moulded together that carry data to different components on the motherboard. There is a wire for each bit of the word or byte and additional wires to coordinate the activity of moving information. They also connect the floppy drives, disk drives and CD-ROM drives to the connectors in the motherboard. Nowadays, Serial Advanced Technology Attachment (SATA) cables have replaced the ribbon cables to connect the drives to the motherboard.
Figure 2.18 Ribbon cables inside a PC
The RAM consists of chips on a small circuit board (Figure 2.19). Two types of memory chips—Single In-line Memory Module (SIMM) and Dual In-line Memory Module (DIMM) are used in desktop computers. The CPU can retrieve information from DIMM chip at 64 bits compared to 32 bits or 16 bits transfer with SIMM chips. DIMM chips are used in Pentium 4 onwards to increase the access speed.
Figure 2.19 RAM memory chip
The disk drives are present inside the machine. The common disk drives in a machine are hard disk drive, floppy drive (Figure 2.20 (i & ii)) and CD drive or DVD drive. High-storage devices like hard disk, floppy disk and CDs (Figure 2.20 (iii) & (iv)) are inserted into the hard disk drive, floppy drive and CD drive, respectively. These storage devices can store large amounts of data, permanently.
The processor or the CPU is the main component of the computer. Select a processor based on factors like its speed, performance, reliability and motherboard support. Pentium Pro, Pentium 2 and Pentium 4 are some of the processors.
Figure 2.20 Storage devices (i) Hard disk drive, (ii) DVD drive, (iii) Floppy disk, (iv) CD
Accelerated Graphics Port |
CPU performance |
Peripheral Component |
(AGP) |
Data bus |
Interconnect (PCI) |
Address bus |
Decoding |
Power On Self Test (POST) |
Arithmetic Logic Unit (ALU) |
Executing |
Primary memory |
Audio plugs |
Expansion bus |
PS/2 Port |
Basic Input Output System |
Expansion card |
Random Access Memory |
(BIOS) |
Expansion slot |
(RAM) |
Billion Instructions Per Second |
Extended Industry Standard |
Read Only Memory (ROM) |
(BIPS) |
Architecture (EISA) |
Reduced Instruction Set |
Brain of computer |
Fetching |
Computer (RISC) |
Bus |
Firewire |
Registers |
Cache memory |
Form factor |
Ribbon cables |
Central Processing Unit (CPU) |
Input/Output (I/O) unit |
SCSI port |
Chipset |
Instruction format |
Serial port |
Complementary Metal-Oxide |
Instruction set |
Speed of computer |
Semiconductor (CMOS) |
Instruction cycle |
Stored program |
Complex Instruction Set Computer |
Memory Unit |
Storing |
(CISC) |
Microprocessor |
System bus |
Computer architecture |
Million Instructions Per Second |
System clock |
Computer design |
(MIPS) |
Universal Serial Bus |
Computer organization |
Motherboard |
(USB) |
Control bus |
Parallel port |
Word size |
Control Unit (CU) |
|
|
Section 2.1
1. Define computer architecture, computer organization and computer design.
2. Give a brief description of the working of the computer.
Section 2.2
3. CPU is also often called the_____of computer.
4. Define a microprocessor.
5. Define a motherboard.
6. The different parts of the CPU are_____, _____ and _____.
7. _____ and _____ are the main memory.
8. What is the purpose of the main memory?
9. List the main functions of the CPU.
Section 2.2.1–2.2.3
10. ALU consists of the _____ unit and _____ unit.
11. What are the functions of the ALU?
12. _____ is also called the working memory of the CPU.
13. List five important registers of the CPU. Also state the purpose of each register.
14. Why are Registers used in the CPU?
15. Define word size.
16. “This is a 64–bit processor”. Explain its meaning.
17. The size of the register is also the _____ size.
18. Which is faster—a 32-bit processor or a 64-bit- processor?
19. What are the functions of the control unit?
Section 2.3–2.3.3
20. Explain the need of the cache memory?
21. The _____ memory is placed between the RAM and the CPU.
22. There are _____ levels of cache memory.
23. Explain the three levels of the cache memory.
24. State three important features of the cache memory.
25. The size of the cache memory is generally in the range _____.
26. What is the purpose of RAM?
27. List the features of the primary memory.
28. List the key features of the secondary memory.
Section 2.4
29. Define the stored program concept.
30. Describe the format of an instruction.
31. The common fields of an instruction are _____ code and _____ code.
32. What is the function of the operand code and the operation code?
Section 2.5
33. Define an Instruction set.
34. What is the significance of the Instruction set in the CPU?
35. “Two processors are compatible”. How do you deduce this statement?
36. Define microarchitecture.
Section 2.6
37. Define an instruction cycle.
38. Give a detailed working of the instruction cycle.
39. Name the four steps involved in an instruction cycle.
40. The number of instructions executed in a second by the CPU, is measured in _____.
Section 2.7
41. The microprocessors are classified as _____ and _____ on the basis of the instruction set.
42. The x86 instruction set of the original Intel 8086 processor is of the _____ type.
43. Describe the features of the CISC architecture.
44. Give two examples of the CISC processor.
45. Describe the features of the RISC architecture.
46. Give two examples of the RISC processor.
47. What is the use of parallel processing and pipelining?
Section 2.8
48. Define a bus.
49. Define a system bus.
50. Define an expansion bus.
51. Why is a bus used?
52. Define—control bus, address bus and data bus.
53. A system bus or expansion bus comprises of three kinds of buses _____, _____ and _____.
54. Name the bus connecting CPU with memory?
55. Name the bus connecting I/O devices with CPU?
Section 2.8.1
56. In a system bus, what is the significance of the control bus, address bus and data bus?
57. The _____ of data bus affects the speed of computer.
58. Name the bus whose width affects the speed of computer?
59. The _____ of address bus determines the maximum number of memory locations the computer can address.
60. Name the bus whose width determines the maximum number of memory locations the computer can address?
Section 2.8.2–2.8.3
61. What are the functions of data bus, address bus and control bus in the expansion bus?
62. Where is the expansion card fixed on the motherboard?
63. What is an expansion slot?
64. Name three common bus technologies.
65. What kind of devices is attached to the PCI bus, AGP bus and USB bus?
Section 2.9
66. List the factors that affect the performance of the computer.
67. Explain in detail the factors that affect the performance of the computer.
68. What is the use of the system clock?
69. The clock frequency is measured in _____.
Section 2.10–2.10.1
70. “The motherboard is characterized by the form factor, chipset and the type of processor socket used”. Explain.
71. Define form factor.
72. Define chipset.
73. _____ is the most common design of the motherboard for desktop computers.
74. What is the significance of the chipset?
75. What is the function of the BIOS?
76. What is the function of the CMOS chip?
77. Explain the booting process when the computer is switched on.
78. What is POST?
Section 2.10.2–2.10.7
79 . List five ports and interfaces available on the backside of the computer to connect the devices.
80. What devices are attached to—(a) Serial Port, (b) Parallel Port, (c) USB Port, (d) Firewire, (e) RJ45 connector, (f) VGA connector, (g) Audio plugs (Line-In, Line-Out and microphone), (h) PS/2 Port, and (h) SCSI Port.
81. List five expansion slots available in the computer.
82. What devices are attached to—(a) ISA slots, (b) PCI slot, (c) AGP slot, (d) PCI Express slot, and (e) PC Card.
83. What is the purpose of the Ribbon cables?
84. Two types of memory chips _____ and _____ are used in desktop computers.
85. List any three storage devices that are attached to the computer.
Extra Questions
86. Give full form of the following abbreviations
87. Write short notes on—
88. Give differences between the following—
3.145.61.170