Fundamentals of Computer Hardware COMP 0003

Transcription

1 Fundamentals of Computer Hardware COMP 0003 Module Notes Department of Computing

2 UNIT 1 PERSONAL COMPUTER Input Devices Following are the most commonly used input devices: Mouse: In its most basic form, the mouse is a handfittine device that uses some form of motion-detection mechanism to translate its own physical towdimensional movement into onscreen cursor motion. Many variations of the mouse exist, including trackballs, tablets, touchpad s, and pointing sticks. Keyboard: The keyboard is easily the most popular input device, so much so that its popularity is more of a necessity. Modern computer keyboards often have separate cursor-movement and numerical keypads. The numerical keys in a row above the alphabet keys send different scan codes to the computer form those sent by the numerical keypad. Keyboards have also added function keys, which are often placed in a row across the top of the keyboard above the numerical row. Barcode Reader: A barcode reader (or barcode scanner) is a specialized input device commonly used in retail and other industrial sectors that manage inventory. The systems that the reader connects to can be so specialized that they have no other input device. Barcode readers can use LEDs or lasers as light sources and can scan one-or two-dimensional barcodes. Multimedia Devices: Two broad categories of multimedia input are audio and video. Digital motion and still cameras are incredibly popular as a replacement for similar video products that do not transfer information to a computer, making sharing and collaboration so much easier than before. Biometric Devices: Any device that measures one or more physical or behavioral features of an organism is considered a biometric device. When the same device forwards the biometric information to the computer, it becomes and input device. The list includes fingerprint scanners, retinal scanners, voice recognition, and facial recognition, to name a few. Touchscreens: Touchscreen technology converts stimuli of some sort, which are generated by actually touching the screen, to electrical impulses that travel Fundamentals of Computer Hardware 1

3 over serial connections to the computer system. These input signals allow for the replacement of the mouse, simultaneously in movement and in click. This technology can also be seen in PDAs, point-of-sale venues for such things as PIN entry and signature capture, handheld and bar-mounted games, ATMs, remote controls, appliances, and vehicles. Display Devices CRT Displays: It is the conventional computer monitor. In a CRT, a device called an electron gun shoots a beam of electrons towards the back side of the monitor screen. The screen glows when electrons strike them. Liquid Crystal Displays (LCDs): LCDs are very compact and used not only in laptops, but also in desktops. It works on the principle that when electric current is passed through a semi-crystalline liquid, crystals align themselves with the current. By combining transistors with these liquid crystals, patterns could be formed. Projection Systems: Video projection systems are units with a lightening system that projects the video display unit s image onto a screen or other flat surface for group viewing. Fundamentals of Computer Hardware 2

4 TV Tuner Cards and Video Capture Cards The TV tuner card is a class of internal and external devices that allows you to connect a broadcast signal, such as home cable television, to your computer and display it. A video capture card can also be a stand-alone device and is often used to save a video stream to the computer for later manipulation or sharing. TV tuner cards and video capture cards need and often come with software to aid in the processing of multimedia input. Network Interface Card (NIC) A network interface card (NIC) is an expansion card that connects a computer to a network so that it can communicate with other computers on that network. NIC can also stand for network interface controller. Modem Any computer that connects to the Internet using a dial-up connection needs a modem, or modulator/demodulator. A modem is a device that converts digital signals from a computer into analog signals that can be transmitted over phone lines and back again. Fundamentals of Computer Hardware 3

5 Motherboard The spine of the computer is the motherboard. It is also known as the system board. It is the most important component in the computer because it connects all the other components of a PC together. On the system board you will find the central processing unit (CPU), underlying circuitry, expansion slots, video components, random access memory (RAM) slots, and a variety of other chips. Types of System Boards Nonintegrated system board- Each major assembly is installed in the computer Fundamentals of Computer Hardware 4

6 as an expansion card. The major assemblies are video circuitry, disk controllers and accessories. It is difficult to find nonintegrated motherboards these days. Integrated system board- Most of the components that would otherwise be installed as expansion cards are integrated into the motherboard circuitry. They are simple and cheaper to produce, but expensive to repair. The main drawback is that when one component breaks, you can t just replace the component that s broken. The whole motherboard must be replaced. System Board Form Factors System boards are also classified by their form factor (design) as: Advanced Technology Extended (ATX): The ATX motherboard has the processor and memory slots at right angles to the expansion cards. This arrangement puts the processor and memory in line with the fan output of the power supply, allowing the processor to run cooler. ATX are the primary motherboards in use today. Micro ATX: Micro ATX follows the same principle of component placement for enhanced cooling over pre-atx designs but with a smaller footprint. New Low-Profile Extended (NLX): Here the expansion slots are placed sideways on a special riser card to use the reduced vertical space optimally. It is used in low profile case types. Fundamentals of Computer Hardware 5

7 Balanced Technology Extended (BTX): This was introduced for hotter running processors. In these boards all the heat producing components are lined between air intake vents and the power supply s exhaust fan. This makes CPU and other components as cool as possible. Chipsets A chipset is a collection of chips or circuits that perform interface and peripheral functions for the processor. These chips provides interface for memory, expansion cards and onboard peripherals. They dictate how a motherboard will communicate with the installed peripherals. Chipsets are given a name and model number by the manufacturer. Fundamentals of Computer Hardware 6

8 Bus Architecture Many components of a computer system work on the basis of a bus. A bus is a common collection of signal pathways over which related devices communicate within the computer system. PCI, AGP etc are expansion buses of various architectures. These expansion buses of various architectures allow insertion of external devices, or adapters into the bus. Expansion Slots These slots are used to install various devices in the computer to expand its capabilities. They look like small plastic slots, usually from 1 to 6 inches long and approximately ½ inch wide. The expansion devices that might be installed in these slots include video, network, sound and disk interface cards. The main types of expansion slots used in computers today are: Peripheral Component Interconnect (PCI): These are short and usually white and can be found in any computer that has a Pentium class processor or higher. Fundamentals of Computer Hardware 7

9 Accelerated Graphics Port (AGP): AGP slots are known mostly for video card use. AGP slots were designed to be a direct connection between the video circuitry and the PC s memory. They are usually brown, located right next to the PCI slots on motherboard, and are slightly shorter than the PCI slots. PCIe: PCI Express is a newer expansion slot. It was designed to be a replacement for AGP and PCI. It has the capability of being faster than AGP while maintaining the flexibility of PCI. Fundamentals of Computer Hardware 8

10 Audio Modem Riser (AMR): The manufacturers developed a way of separating the analog circuitry, for example modem and analog audio to its own card. This allowed the analog circuitry to be separately certified. Communications and Networking Riser (CNR): This can be found on some Intel motherboards as a replacement for Intel s AMR slots. These slots have motherboard chipsets with certain integrated features. If the built-in features of that chipset need to be enhanced, a CNR riser card could be added to enhance the onboard capabilities. Additional advantages of CNR over AMR include networking support, Plug and Play compatibility, support for hardware acceleration etc. Fundamentals of Computer Hardware 9

11 BIOS and POST Basic Input/ Output System (BIOS) chip is a special memory chip contains the BIOS systems software that boots the system and allows the operating system to interact with certain hardware in the computer, in lieu of requiring a device driver to do so. A major function of the BIOS is to perform a process known as power-on self-test (POST). POST is a series of system checks performed by the system BIOS. The POST verifies the integrity of BIOS itself. It also verifies and confirms the size of primary memory. During POST, the BIOS analyze and catalog other forms of hardware such as buses and boot devices. The BIOS is responsible for offering the user a key sequence to enter the configuration routine as POST is the beginning. CMOS and CMOS Battery Your PC has to keep certain settings when it s turned off and its power cord is Fundamentals of Computer Hardware 10

12 unplugged. These settings include the following: - Date - Time - Hard drive configuration - Memory Integrated ports - Boot sequence - Power management - Your PC keeps these settings in a special memory chip called the complementary metal oxide semiconductor (CMOS) memory chip. Actually, CMOS is a manufacturing technology for integrated circuits. CMOS memory is usually not upgradable in terms of its capacity and might be integrated into the BIOS chip or some other chip. To prevent CMOS from losing its rather important information, motherboard manufacturers include a small battery called the CMOS battery to power the CMOS memory. The batteries come in different shapes and sizes, but they all perform the same function. Memory Packaging The memory slots on a motherboard are designed for particular module form factors or style. - DIMM - RIMM - SODIMM - MicroDIMM DIMM stands for dual inline memory module. DIMMs are 64-bit memory modules that are used as package for the SDRAM family: SDR, DDR, DDR2, and DDR3. DIMM differentiate the functionality of the pins on one side of the module from the corresponding pins on the other side. Fundamentals of Computer Hardware 11

13 RIMM stands for Rambus inline memory module. A RIMM is a custom memory module that carries DRDRAM and varies in physical specification, based on whether it is a 16-bit or 32-bit module. The 16-bit modules have 184 pins and two keying notches, while 32-bit modules have 232 pins and only one keying notch. SODIMM: Notebook computers and other computers that require much smaller components don t use standard RAM packages, such as the SIMM or the DIMM. SODIMMs are available in many physical implementations, including the older 32-bit (72- and 100-pin) configuration and newer 64-bit (144-pin SDR SDRAM, 200-pin DDR/DDR2, and 204-pin DDR3) configurations. MicroDIMM: A newer, and smaller, RAM form factor is the MicroDImm. The MicroDIMM is an extremely small RAM form factor. In fact, it is over 50 percent smaller than a SODIMM. It was designed for the ultralight and portable subnotebook style of computer. Common Peripheral Interfaces and Cables An interface is a method of connecting two dissimilar items together. A peripheral interface is a method of connecting a peripheral or accessory to a computer, including the specification of cabling, connector and port type, speed, and method of communication used. The most common interfaces used in PCs today include: - Parallel - Serial - USB - IEEE 1394 (FireWire) - Infrared Parallel: The parallel interface transfers data 8 bits at a time over eight separate transmit wires inside a parallel cable (one bit per wire). Normal parallel interfaces use a DB-25 female connector on the computer to transfer data to peripherals. Fundamentals of Computer Hardware 12

14 Serial: In serial communications, bits of data are sent one after another (single file, if you will) down one wire, and they return on a different wire in the same cable. Three main types of serial interfaces are available today: standard serial, Universal Serial Bus (USB), and FireWire. Universal Serial Bus (USB): USB cables are used to connect a wide variety of peripherals to computers, including keyboards, mice, digital cameras, printers and scanners. The connectors are identical, so perhaps look for cables that are transparent with a view to the silver metallic shielding within. It was designed to be Plug and Play-just plug in the peripheral. Fundamentals of Computer Hardware 13

15 IEEE 1394 (FireWire): Although most people think of FireWire as a tool for connecting their digital camcorders to their computers, it s much more than that. Because of its high data transfer rate, it is being used more and more as a universal, high-speed data interface for things like hard drives, optical drivers, and digital video editing equipment. Storage Devices Hard Disk Drive Systems: Hard disk drive (HDD) systems (hard disks or hard drives for short) are used for permanent storage and quick access. Hard disks typically reside inside the computer, where they are semi permanently mounted with no external access (although there are external and removable hard drives. Fundamentals of Computer Hardware 14

16 Floppy Drives: A floppy disk (or floppy diskette) is a magnetic storage medium that uses a diskette made of thin, flexible plastic enclosed in a protective casing. The floppy disk once enabled information to be transported from one computer to another very easily. Today, floppies are a little too small in capacity to be efficient anymore. Optical Storage Drives: Most computers today have an optical storage drive, such as a CD (compact disc) or DVD (digital versatile disc or digital video disc) drive. Such optical storage devices have replaced floppy diskette drives. Although these discs have greater data capacity and increased performance over floppies, they are not meant to replace hard disk drive. The CDs and DVDs used for data storage are virtually the same as those used for permanent records audio and video. Removable Storage Tape Backup Devices: An older form of removable storage is the tape backup. Tape backup devices can be installed internally or externally and use either a digital or analog magnetic tape medium instead of disks for storage. They hold much more data than any other medium but are also much slower. They are primarily used for archival storage, not interactive storage. Fundamentals of Computer Hardware 15

17 Thumb Drives: Also known as USB flash drives, thumb drives are incredibly versatile and convenient devices that allow you to store large quantities of information in a very small form factor. USB-Attached External Disk Drives: Many external optical and hard disk drives today are manufactured into their own chassis and have detachable connectivity for USB (and/or FireWire) LAPTOP COMPONENTS Laptop Case A typical laptop case is made up of three main parts: The display-usually an LCD display The case frame, which is the metal reinforcing structure inside the laptop that provides rigidity and strength and that most components mount to. The case or the plastic cover that surrounds the components and provides protection from the elements. Laptop Motherboards The primary differences between a laptop motherboard and a desktop motherboard are the lack of standards and the much smaller form factor. As mentioned earlier, most motherboards are designed along with the laptop case so that all the components will fit inside. Fundamentals of Computer Hardware 16

18 To save space, components of the video circuitry (and possibly other circuits as well are placed on a thin circuit board that connects directly to the motherboard. This circuit board is often known as a daughterboard. Laptop Processors Streamlined connection to the motherboard: Laptop processors are generally either soldered directly to the motherboard or attached using the Micro-FCBGA (Flip Chip Ball Grid Array) standard, which uses balls instead of pins. In most cases, this means that the processor cannot be removed, meaning no processor upgrades are possible. Lower voltages and clock speeds: Two ways to combat heat are to slow the processor down (run it at a lower speed) or give it less juice (run it at a lower voltage). Again, performance will suffer compared to a desktop processor, but lowering heat is the goal here. Active sleep and slowdown modes: Most laptops will run in a lower power state when on battery power, in an effort to extend the life of the battery. This is known as processor throttling. The motherboard works closely with the operating system to determine if the processor really needs to run at full speed. If it doesn t, it s slowed down to save energy and to reduce heat. Memory Notebooks don t use standard desktop computer memory chips, because they re too big. If you wanted to add memory to your laptop, you had to order it from the laptop manufacturer. However, there are now two common types of laptop memory package: SODIMM and MicroDIMM. Fundamentals of Computer Hardware 17

19 SODIMM: The most common memory form factor for laptops is called a Small Outline DIMM (SODIMM). They re much smaller than standard DIMMs. Just like with desktop computers, make sure the SODIMM you want to put into the laptop is compatible with the motherboard. The same standards that apply to desktop memory compatibility apply to laptops. This means you can find DDR, DDR2, and DDR3 SODIMMs for laptops. MicroDIMM: Although no longer new, the MicroDIMM is the most recent form factor for laptop memory modules. The MicroDIMM is an extremely small RAM form factor. It was designed for the ultralight and portable subnotebook style of computer. Storage Nearly all laptops have a hard drive, but not all laptops have both a floppy drive and optical drive. In some cases, the floppy drive is an external device that you connect with a special cable to a proprietary connector. Mice and Pointing Devices In addition to the keyboard, you must have a method of controlling the onscreen pointer in the Windows interface. There are many methods of doing this, but the most common are - Trackball - Touchpad - Point stick - Touchscreen Expansion Buses and Ports PCMCIA (PC Card) Expansion Bus: PCMCIA stands for Personal Computer Memory Card International Association. The PCMCIA was organized to provide a standard way of expanding portable computers. The PCMCIA bus was originally designed to provide a way of expanding the memory in a small, handheld computer, referred to generically as a PCMCIA host. The interface is a thin, 68- pin connector that has reminder relatively unchanged from the original specification. Docking Stations Some laptops are designed to be desktop replacement laptops. A docking port is Fundamentals of Computer Hardware 18

20 used to connect the laptop to a special laptop-only peripheral known as docking station. A docking station is basically an extension of the motherboard of a laptop. Because a docking station is designed to stay behind when the laptop is removed, it can contain things like a full-sized drive bay and expansion bus slots. Also, the docking station can function as a port replicator. Power System Portable computers can use either of two power source: batteries or adapted power form an AC or DC source. Regardless the source of their power, laptops utilizes DC power to energize their internal components. Printers The following are the different types of printers: Impact Printers The most basic type of printer is the category known as impact printers. Impact printers, as their name suggests, use some form of impact and an inked ribbon to make an imprint on the paper. In a manner of speaking, typewriters are like impact printers. Both use an inked ribbon and an impact head to make letters on the paper. The major difference is that the printer can accept input form a computer. There are two major types of impact printers: daisy wheel and dot matrix. Bubble-Jet Printers Fundamentals of Computer Hardware 19

21 The next category of printer technology is one of the most popular in use today. This category is an advanced form of an older technology known as inkjet printers. Both types of printers spray ink on the page, but inkjet printers used a reservoir of ink, a pump, and an ink nozzle to accomplish this. They were messy, noisy, and inefficient. Bubble-jet printers work much more efficiently and are much cheaper. Laser Printers Laser printers and inkjet printers are referred to as page printers because they receive their print job instructions one page at a time. Laser printer uses a combination of static electric charges, laser light and a black powdery substance called toner. Cleaning, charging, writing, developing, transferring and fusing are the steps involved for producing images on a paper by the laser printer. Fundamentals of Computer Hardware 20

22 Unit II Central Processing Unit External Data Bus The external data bus (also known as the external bus or simply data bus) is the primary route for data in a PC (personal computer). All data-handling components or optional data devices are connected to it; Therefore, any information (code) placed on that bus is available to all devices connected to the computer. Early computers used eight conductors (an 8-bit data bus), which allowed for the transfer of 1 byte of information at a time. Now, the width of the external data bus increased to 16, 32, and the current width of 64 conductors. The wider bus lets more data flow at the same time, just as adding more lanes to a highway allows more cars to move through a point in a given amount of time. To understand how a computer moves data between components, visualize each device on the data bus (including the CPU) connected to the bus by means of a collection of onoff switches. By assessing which conductors have power and which ones do not, the device can read the data as it is sent by another device. The on-off state of a line gives the value of 0 (off) or 1 (on). The wires spell out a code of binary numbers that the computer interprets and then routes to another system component or to the user by means of an output device such as a monitor or printer. Communication occurs when voltage is properly applied to or read from any of the conductors by the system. Figure illustrates a data bus connected to a CPU and a device. Fundamentals of Computer Hardware 21

23 Coded messages can be sent into or out of any device connected to the external data bus. Think of the data bus as a large highway with parallel lanes. Extending that analogy, bits are like cars traveling side by side each carries part of a coded message. Microprocessors are used to turn the coded messages into data that performs a meaningful task for the computer's user. CPU The CPU is the part of a computer in which arithmetic and logical operations are performed and instructions are decoded and executed. The CPU controls the operation of the computer. Some functions are handled by support chips, which are often referred to collectively as a chip set. Transistors The main components of microprocessors, are small, electronic switches. The on off positions of the transistors form the binary codes Although transistors might seem simple, their development required many years of painstaking research. Before transistors were available, computers relied on slow, inefficient vacuum tubes and mechanical switches to process information. The first large-scale computers took up a huge amount of space, and technicians actually went inside them to "program" by turning on and off specific tubes! Many materials, including most metals, allow electrical current to flow through them; these are known as electrical conductors. Materials that don't pass electrical current are called insulators. Pure silicon, which is used to make most transistors, is a semiconductor; its degree of conductivity can be adjusted, or modulated, by adding impurities during production. Transistor switches have three terminals: The source, the gate, and the drain. When positive voltage is applied to the gate, electrons are attracted, forming an electron channel between the source and the Fundamentals of Computer Hardware 22

24 drain. Positive voltage applied to the drain pulls electrons from the source to the drain, turning the transistor on. Removing the voltage turns it off by breaking the pathway. In the late 1950s, a major development in transistor technology took place. A team of engineers put two transistors on a silicon wafer, creating the world's first IC and paving the way for the development of compact computers. Integrated Circuits An IC is an electronic device consisting of a number of miniature transistors and other circuit elements (resistors and capacitors, for instance). An IC functions just as a large collection of these parts would, but it is a fraction of the size and uses a fraction of the power. ICs make today's microelectronics possible. The original transistors were small plastic boxes about the size of a peanut that could handle only one function. The word integrated denotes that IC devices combine many circuits and some of their functions into one package. A prime example of this technology is the microprocessor. Microprocessors A microprocessor is an integrated circuit (IC) that contains a complete CPU on a single chip PC Microprocessor Developments & Features Microprocessor Microprocessors are usually divided into three subsystems: The control unit (CU), The arithmetic logic unit (ALU), And the input/output (I/O) unit. The term CPU is used to denote a combined CU and ALU, contained in a single package. The advent of the CU marked a radical improvement in processor design Fundamentals of Computer Hardware 23

25 Allowing CPU operations to be based in part on code provided by an external program like a BIOS (basic input/output system). This extended the ability of a PC to use new hardware components that were not part of the original design. The ALU the part of the IC that handles the basic math functions of computation. The I/O unit fetches data from the outside and passes data back to the external bus. Registers Registers are temporary memory storage areas used during data manipulation. Physically, registers are rows of microscopic switches that are set on or off. Each row forms a binary number: off = 0 and on = 1. Hence (reading from right to left) off.off.on equals the number 1. Off.on.on equals the number three ( ). The CPU uses registers, like scratch pads, to hold data while it works on a task. Changes in data during an operation are also stored in a register, then sent out to other components as the job is finished. The number and width of a register vary from one type of machine to another. The wider the register, the more bits the machine can handle at one time just as with the width of the external bus. As register width moved from 4 to 8 to 16 to 32 to 64 to 128 bits, PCs increased in performance. CPU Clock Timing is essential in PC operations. Without some means of synchronization, chaos would ensue.] Timing allows the electronic devices in the computer to coordinate and execute all internal commands in the proper order. Placing a special conductor in the CPU and pulsing it with voltage creates timing. Each pulse of voltage received by this conductor is called a clock cycle. All the switching activity in the computer occurs while the clock is sending a pulse Virtually every computer command needs at least two clock cycles. Some commands might require hundreds of clock cycles to process. Clock Speed Fundamentals of Computer Hardware 24

26 It is common for computers to be marketed to consumers based on features that show off their best points. One main selling point is The system clock rate, which is measured in megahertz (MHz), or millions of cycles per second. The clock rate suggests how many commands can be completed in two cycles (the minimum time required to execute a command). The process of adding two numbers together would take about four commands (eight clock cycles). A computer running at 450 MHz can do about 44 million simple calculations per second. Clock speed is determined by the CPU manufacturer and represents the fastest speed at which the CPU can be reliably operated. The Intel 8088 processor, as used in the original IBM PC, had a clock speed of 4.77 MHz. Today's processors have clock speeds that run up to and, in some cases, exceed 750 MHz. A computer has two clocks: one to set the speed and timing and a second clock to keep time for date and time calculations. They are two entirely different devices. Memory The CPU can only hold a limited amount of information. To compensate, additional chips are installed in the computer for the sole purpose of temporarily storing information that the CPU needs. These chips are called RAM (random access memory). The term random access is used because the CPU can place or retrieve bytes of information in or from any RAM location at any time. Address Bus The content of RAM is constantly changing as programs and the computer itself use portions of it to note, calculate, and hold results of actions. It is essential for the system to know what memory is assigned to which task and when that memory is free for a new use. To do so, the system has to have a way to address segments of memory and to Fundamentals of Computer Hardware 25

27 quickly change the holdings in that position. The portion of the PC assigned this task is the address bus. PC Microprocessor Developments and Features Microprocessors have evolved from the 4004 into today's high-speed Pentiums. Each new processor has brought higher performance and spawned new technology. Six basic elements are customarily used to gauge the performance and capability of a CPU design. Speed. The maximum number of clock cycles measured in MHz. The higher the speed, the quicker a command will be executed. Number of transistors. More switches means more computing power. Registers. The size (in bits) of the internal registers. The larger the registers, the more complicated the commands that can be processed in one step. External data bus. As data bus size increases, so does the amount and complexity of code (information) that can be transferred among all devices in the computer. Address bus. The size of the address bus determines the maximum amount of memory that can be addressed by the CPU. Internal cache. The internal cache is high-speed memory built into the processor. This is a place to store frequently used data instead of sending it to slower devices (speed is relative in computers) such as RAM and hard disk drives It is built into the processor and has a dramatic effect on speed. Virtual Memory Virtual memory is the art of using hard disk space to hold data not immediately required by the processor; it is placed in and out of RAM as needed. using virtual memory slowed the system down (electronic RAM is much faster than a mechanical hard drive), it allowed the 286 to address up to 1 gigabyte (1 GB = 1000 MB) of memory (16 Fundamentals of Computer Hardware 26

28 MB of actual memory and 984 MB of virtual memory). Virtual memory required the use of operating systems more advanced than MS- DOS, leading to the development of products such as Microsoft Windows, IBM OS/2, and SCO's (Santa Cruz Operation) PC version of UNIX Replacing and Upgrading a CPU There are a number of issues to think about when deciding whether to upgrade a CPU or replace a machine altogether. Perhaps the most important issue is the value of the upgrade. There are limits to what can be upgraded and the results that can be expected from the upgrade. A poor upgrade can lead to total failure and could ultimately require replacement of the motherboard. Again, the best source of information regarding CPU upgrades is the documentation that comes with the motherboard. The following table lists several possible scenarios for upgrading a CPU. it is more cost-effective to replace an entire motherboard than it is to upgrade a CPU. Make sure that the new motherboard will fit into the computer case (check size and alignment of expansion buses) before starting the installation. Be sure that the power supply of the old case and new motherboard are of the same type with the proper connectors (such as AT, ATX). Always make sure that you can return a CPU and mother-board to the vendor if they won't fit.. Keep in mind that many suppliers charge a restocking fee of 15 to 20 percent for returns. Inserting a CPU There are several types of CPU sockets available. Today virtually all desktop PCs come with some variation of the SEC packaging. Fundamentals of Computer Hardware 27

29 Low-insertion-force (LIF) Zero-insertion-force (ZIF) LIF Socket Sockets commonly used for early generation computer processors. Flat-head screwdriver or a plate cover for an expansion card slot will also work. Evenly around the CPU or you will risk damaging the CPU, the socket, or both ZIF Socket ZIF Socket was the most popular mount for desktop and tower PCs with 486 and early Pentium CPUs. A ZIF socket has a lever arm that allows for simple removal and installation of CPUs. ZIF sockets were introduced during the early 1990s as a safe means of providing a user-friendly CPU upgrade. The first ZIF socket had 169 pins and was used on 486SX systems. These systems were sold with a 486SX chip already installed in a PGA socket and provided a ZIF socket for a 486 OverDrive chip, a special processor designed to increase the speed of 486 computers. (It works much like the standard clock-doubling processors DX2 and DX4 used on 486 motherboards.) Fundamentals of Computer Hardware 28

30 Unit-III Power Supplies Overview of Power Supplies A standard power supply draws power from a local, alternating current (AC) source (usually a wall outlet) and converts it to either 3.3 or 5 volts direct current (DC) for on-board electronics, and 12 volts DC for motors and hard drives. In all cases, it delivers both positive and negative DC to the computer. Power supplies must "condition" the power, smoothing out any radical changes in its quality. Many homes and offices have power that fluctuates far more than the delicate parts of a PC can tolerate and survive under. PC power supplies also electricity to the system's cooling and processor fans that keep the machine from overheating. If the power supply or its fan should fail or cause erratic behavior by the PC, the power supply must be replaced. (Although it is possible to remove and replace a power supply fan, the low cost of a power supply makes it more practical to replace the power supply itself.) Most supplies have a universal input that will accept either 110 volts alternating current (VAC), 60 hertz (Hz) (U.S. standard power), or 220 VAC, 50 Hz (European and Asian standard). When replacing a power supply, there are three things to consider: physical size, wattage, and connectors. A hertz is a measure of unit frequency: 1 cycle per second equals 1 hertz. A kilohertz (khz) is 1,000 cycles per second; a megahertz (MHz) is 1 million cycles per second. Power Supply Wattage Power supplies are rated according to the maximum sustained power (measured in watts) that they can produce. Fundamentals of Computer Hardware 29

31 A watt is a unit of electrical power equivalent to one volt-ampere. the power supply must produce at least enough energy to operate all the components of the system at the same time. Servers and high-performance workstations often have an abundance of random access memory (RAM), multiple drives, SCSI (Small Computer System Interface) adapters, and power-hungry video cards, along with one or more network cards. They often demand power supplies of watts. Power Supply sizes AT Older Pentium-based computers and all 486-based and earlier PCs ATX All Pentium II and later based systems On AT-style PCs, it comes from power supply. The on-off power control circuit boards is build into the motherboard Style power supplies connect to the motherboard through a pair of sixwire connectors. Style power supplies connect through a single 20-pin connector Power Supply Connectors Power supplies employ several types of connectors, all of which are easy to identify and use. On the outside of the computer enclosure, a standard male AC plug and three-conductor wire (two power wires and a ground)draws current from a wall outlet, with a female connection entering the receptacle in the back of the power supply. There are three types of connectors on the inside: the power main to the motherboard Fundamentals of Computer Hardware 30

32 And two types of four-pin fittings to supply 5 volts and 3.3 volts of power to peripherals such as the floppy disk and hard disk drives. Connections to Peripheral Hardware Two standard types of connectors are used to connect the power supply to peripheral hardware: Molex connector. most commonly used power connector. It provides both 12-volt and 5-volt power. Hard disk drives, internal tape drives, CD-ROM drives, DVD (digital video disc) drives, and older 5.25-inch floppy disk drives all use this fitting. The Molex connector has two rounded corners and two sharp corners to ensure that it installs properly Figure: Molex connector Mini connector. Most power supplies provide one or more mini connectors The mini is used primarily for 3.5-inch floppy disk drives. It has four pin-outs and, usually, four wires. Most are fitted with keys that make it difficult to install upside down. orient the connector correctly; applying power with the connector reversed can damage or destroy the drive. Figure: Mini connector Fundamentals of Computer Hardware 31

33 Two- and Three-Pin Mini Plugs A less common type of power connector is used to connect the fan of a Pentium II or III processor to the motherboard for power, to connect a CD-ROM drive to a sound card, and to provide power for 3.5-inch floppy disk drives. These connectors have two or three wires that are usually red and black or red, yellow, and black. Extenders & splitters: PCs can run out of power connections, and large cases can have drives beyond the reach of any plug on the supply. A good technician has a quick solution on hand to both of these common problems: extenders and splitters. Extenders are wire sets that have a Molex connector on each end; are used to extend a power connection to a device beyond the reach of the power supply's own wiring. Splitters are similar to extenders, with the exception that they provide two power connections from a single power supply connector. Power Failures: Power supplies are affected by the quality of the local power source. Common power delivery problems such as spikes, surges, sags, brownouts, and blackouts affect the stability and operation of the main power supply and are passed on to the computer. computers and other sensitive electronics are affected by this. Although we can't fully control these problems, there are a few things we can do, to protect our equipment and data and ensure a reasonably clean electrical supply. Connecting a Peripheral Hardware Problem Surges Description These are brief (and sometimes catastrophic) increases in the voltage source (very high voltage for a very short time). They can originate with the power Fundamentals of Computer Hardware 32

34 source (the local power company) but most often are due to lightning strikes. Spikes are very short over voltage conditions. Spikes are measured in Spikes nanoseconds, whereas a surge is measured in milliseconds. Sags These are brief decreases of voltage at the power source. If a sag lasts longer than 1 second, it is called a brownout. The overloading of Brownouts a primary power source can cause brownouts. A blackout is a complete power failure, which can be caused by equipment failure (local or regional) or accidental cutting of power cables. When the Blackouts power returns after a blackout, there is a power spike and the danger of a power surge. Fundamentals of Computer Hardware 33

35 Unit-IV Memory Nonvolatile & Volatile Memory There are two major classes of computer memory: nonvolatile and volatile. Nonvolatile memory is retained even if the power to the computer is shut off. The setup data held in CMOS (complementary metal-oxide semiconductor), is a good example of nonvolatile memory. If the data is lost when the computer loses power, the memory is said to be volatile. Active memory is a state in which a block of code or data is directly accessible to the CPU for reference or manipulation. When data is located outside the system's active memory, it is said to be in storage. Storage devices include floppy disk and hard disk drives, optical media, and tape units. Active memory is faster than storage because the information is already on the system, there are fewer physical operations involved in obtaining the data, and the CPU has direct control over the memory. ROM ROM (read-only memory) is nonvolatile memory, generally installed by the vendor of the computer during the process of manufacturing the motherboard or secondary components that need to retain code when the machine is turned off. With the use of ROM, information that is required to start and run the computer cannot be lost or changed. ROM is used extensively to program operation of computers, as well as in devices like cameras and controls for the fuel injectors in modern cars. However, ROM plays a limited role in the PC (personal computer). Fundamentals of Computer Hardware 34

36 Here, it holds the instructions for performing the power-on self test (POST) routine and the BIOS (basic input/output system) information used to describe the system configuration. RAM RAM (random access memory) is what is most often referred when PC memory is discussed. RAM is the form of volatile memory used to hold temporary instructions and data for manipulation while the system is running. The term random is applied because the CPU can access or place data to and from any addressable RAM on the system. If power to the system is lost, all RAM is lost as well. Usually, when referring to RAM, we are speaking of some variation of DRAM (dynamic RAM) or SDRAM (synchronous DRAM). These are the most common forms of RAM used in the modern PC. DRAM works by using a microscopic capacitor and a microscopic transistor to store each data bit. A charged capacitor represents a value of 1, and a discharged capacitor represents a value of 0. A capacitor works like a battery it holds a charge and then releases it. The tiny capacitors in DRAM hold their charges for only fractions of a second. DRAM needs an entire set of circuitry just to keep the capacitors charged. The process of recharging these capacitors is called refreshing. Without refreshing, the data would be lost. This is another reason DRAM is called volatile memory. Each transaction between the CPU and memory is called a bus cycle. The amount of memory that a CPU can address in a single bus cycle has a major effect on overall system performance and determines the design of memory that the system can use. EPROM (Erasable PROM) All the information in this memory can be erased by exposing the chip to ultra violet Fundamentals of Computer Hardware 35

37 light through a quartz window. This chip can be reprogrammed later. Because the chip can be revised many times this memory is suited for product development, Experimental projects and college labs. The disadvantage of EPROM is It must be taken out of the circuit to erase it The entire chip must be erased The erasing process takes 15 to 20 minutes. EEPROM (Electrically Erasable PROM) The memory is functionally similar to EPROM Except that information can be altered by using electrical signals at the register level rather than erasing all the information. Error Detection Techniques All computers have some form of memory controller, Which handles the movement of data to and from the CPU and the system memory banks The memory controller is also responsible for the integrity of the data as it is swapped in and out. There are two primary methods of ensuring that the data received is the same as the data sent: 1. parity 2. error-correction coding (ECC). Parity Parity is a method of ensuring data integrity that adds an extra bit (the parity bit) along with each 8-bit bus cycle. There are two kinds of parity: even and odd. Both use a three-step process to validate a bus transaction; however, they do it in opposite ways. In Step 1, both methods set the value of the parity bit based on the even or odd number that represents the sum of the data bits as the first step. Fundamentals of Computer Hardware 36

38 In Step 2, the string goes into DRAM. In Step 3, the parity circuit checks the math. If the parity bit matches the parity bit of the number that represents the sum of the binary string sent, the data is passed on. If it fails the test, an error is reported. Just how that error is handled and reported to the user varies with each operating system. ECC A more robust technology, ECC can detect errors beyond the limits of the simpler parity method. It adds extra information about the bits, which is then evaluated to determine if there are problems with individual bits in the data string. Access Speed Access speed, denoted in nanoseconds (ns), Is the amount of time it takes for the RAM to provide requested data to the memory controller. Here, smaller is better. Be sure to buy RAM that is at least as fast as that listed as standard for the computer in question. A typical total response time for a 70-ns DRAM chip is between 90 and 120 ns. This includes the time required to access the address bus and data bus. Most 486- and Pentium-based machines use either 70-ns or 60-ns DRAM chips, although 50-ns chips are now available. The access speed of a chip is usually printed on the chip (often as part of the identification number). Here are a few important things to remember about access speed when adding memory: Any add-on memory should be the same speed as or faster (lower number) than any existing memory. You cannot mix memory modules with different speeds in the same bank (a bank is a set of several memory modules). You should check the motherboard specifications for the recommended memory chip speed. Fundamentals of Computer Hardware 37

39 Cache Memory To cache is to set something aside, or to store for anticipated use. o Caching, in PC terms, is the holding of a recently or frequently used code or data in a special memory location for rapid retrieval. o Speed is everything when it comes to computers. o Mass storage is much slower than RAM, o and RAM is much slower than the CPU. o The high-speed memory chip generally used for caching is called static RAM (SRAM). Universal Serial Bus(USB) The newest addition to the general PC bus collection, the USB connects external peripherals such as mouse devices, printers, modems, keyboards, joysticks, scanners, and digital cameras to the computer. The USB port is a thin slot; most new motherboards offer two, located near the keyboard. They can also be provided through an expansion card. I/O Address The bus system establishes a connection between the CPU and expansion devices and provides a path for the flow of data. The computer needs a way to track and control which device is sending data and which device is receiving; without such a means the bus system there would be complete chaos. The first step to establishing orderly communication is to assign a unique I/O address to each device. I/O addresses are patterns of 1s and 0s transmitted across the address bus by the CPU. The CPU must identify the device before any data is placed on the bus. Direct Memory Access The CPU runs the BIOS, operating system, and applications, and it also handles interrupts and accesses I/O addresses. This requires the CPU to move a lot of data, using considerable CPU power and time for what is essentially a simple task. Therefore, moving data is a waste of the CPU's resources. To reduce this waste, another chip is installed to work with the system CPU called a DMA chip. The only function of the DMA chip is to move data. It handles all the data Fundamentals of Computer Hardware 38

40 passing from peripherals to RAM and vice versa. COM and Ports IBM created preset combinations I/O addresses for serial and parallel devices. These preset combinations are called ports. The word port simply means a portal or two-way access. The preset combinations are called COM ports for serial devices and LPT (line printer) ports for parallel devices. The purpose of a port is to make installation easier. Parallel Printer Cables Parallel printer ports and cables are used to connect printers and other add-on items such as CD-ROM drives, tape drives, and scanners. Null Modem Cables Null modem cables are used to directly connect two computers together without the need for a modem. SCSI Cables SCSI cables come in a variety of sizes depending on the type of SCSI used and the manufacturer of the device. Typically, internal cables are flat ribbon types and external cables are shielded bundles. Keyboard Cables Another peripheral device with a cable that we encounter and yet never think about is the keyboard. There are different types of keyboard cables (and connectors). Fundamentals of Computer Hardware 39