Repair and Maintenance PC System Components

7/23/2019 Repair and Maintenance PC System Components

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Computer repair and Maintenance Nkumba University

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LECTURE ONE

PC System Components


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The PC system Components

A modern PC is both simple and complicated. It is simple in the sense that over the years,

many of the components used to construct a system have become integrated with other

components into fewer and fewer actual parts. It is complicated in the sense that each part in

a modern system performs many more functions than did the same types of parts in oldersystems. The table below summarizes the basic components required to assemble a typical PCsystem

Table: Basic PC system components

Component Description

1 MotherboardThe motherboard is the core of the system. It really is the PC; everything else is

connected to it, and it controls everything in the system.

2 ProcessorThe processor is often thought of as the engine of the computer. Its also called

the CPU (central processing unit).

3 Memory

The system memory is often called RAM (for random access memory). This is the

primary memory, which

(RAM) holds all the programs and data the processor is using at a given time

4Case/chassis The case is the frame or chassis that houses the motherboard, power supply, disk

drives, adapter cards, and any other physical components in the system.

5 Power supply The power supply feeds electrical power to every single part in the PC.

6

Disk Drives (Floppy,

Hard disks, optical)

The floppy drive is a simple, inexpensive, low-capacity, removable-media,

magnetic-storage device. Many recent systems use other types of removable

magnetic or USB-based flash memory devices instead of floppy drives for

removable storage.

The hard disk is the primary archival storage memory for the system.

CD (compact disc) and DVD (digital versatile disc) drives are relatively high-

capacity, removable media, drive optical drives; many recent systems include arewriteable CD (CD-RW) along with or combined with a DVD-ROM drive.

7 KeyboardThe keyboard is the primary device on a PC that is used by a human to

communicate with and control a system.

8 MouseAlthough many types of pointing devices are on the market today, the first and

most popular device for this purpose is the mouse.

9 Video card* The video card controls the information you see on the monitor

10 Sound card* It enables the PC to generate complex sounds.

11 Cables (power & data)

Power cables help distribute power to the components

Data cables help transfer data from archival storage memory to the processor

and back


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The computer Motherboard

Without a doubt, the most important component in a PC system is the motherboard (which isalso known as main board or system board). The motherboard is the main board in your

computer that contains the BIOS chips, RAM, I/O ports, and CPU. This board maintains theelectrical pathways that enable all other components to communicate with each other

Motherboard Form Factor

The termform factor is used to refer to the physical size and shape of a device.

Motherboard form factor is the physical dimensions (size and shape) as well as I/Oconnection schemes, screw hole, and other positions that dictate into which type of case the

board will fit, as well as power-supply compatibility. Some are true standards (meaning thatall boards with that form factor are interchangeable), whereas others are not standardized

enough to allow for interchangeability. These factors must be considered when assembling a

new system from components and in repair and upgrade situations in which the motherboardmust be replaced

There are a number of motherboard form factors, for example AT, ATX, micro ATX, BTX, LPX,NLX, etc. the figure below shows a micro ATX motherboard form factor.

Figure: A typical micro-ATX motherboard

Expansion Bus Slots

RAM Memory Slots(DIMM)

Hard drive andfloppy drive

connectors

Processor(CPU) socket

Rear panelconnectors

Motherboard powerconnector

Battery

ROM BIOS chip

AGP Slot


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The figure below shows an ATX motherboard and rear panel connections from systems withonboard sound and video (top and middle), networking and IEEE 1394/FireWire (middle and

bottom), and a legacy-free system (bottom).

Figure: ATX motherboard and rear panel connections


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The standard form factor used for LPX and mini-LPX motherboards in many typical low-costsystems is shown in Figure below

.

Figure LPX motherboard back panelconnectors

Figure:Typical LPX system chassis and motherboard


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Motherboard Components

A modern motherboard has several components built in, including various sockets, slots,

connectors, chips, and so on. This section examines the components found on a typical

motherboard.

Most modern motherboards have at least the following major components on them:

a. Processor socket/slot

b. Chipset (North/South Bridge or memory and I/O controller hubs)c. Super I/O chipd. ROM BIOS (Flash ROM/firmware hub)

e. RAM memory slots /sockets (e.g. DIMM, RIMM, SIMM)

f. Expansion bus slots (e.g. PCI, AGP, ISA)g. CPU voltage regulator

h. Batteryi. Power socket

Some motherboards also include integrated video, audio, networking, SCSI, Audio ModemRiser (AMR), Communications and Networking Riser (CNR) connectors, or other optionalinterfaces, depending on the individual board.

In the section below, I discuss only the most important of these components

a. Processor Sockets/Slots

The CPU is installed in either a socket or a slot, depending on the type of chip.

Starting with the 486 processors, Intel designed the processor to be a user-installable andreplaceable part and developed standards for CPU sockets and slots that would allow differentmodels of the same basic processor to plug in. One key was to use a zero insertion force (ZIF)

Figure:NLX motherboard and riser combination


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socket design, which meant that the processor could be easily installed or removed with notools. ZIF sockets use a lever to engage or release the grip on the chip, and with the leverreleased, the chip can be easily inserted or removed.

The ZIF sockets are usually designated with imprint or emboss on the socket indicating what

type it is. Different socket types accepted different families of processors. Therefore knowingthe type of processor socket or slot on a motherboard essentially means knowing which types

of processors are designed to plug in. ( More information about processors is covered in thelecture about processors)

b. Chipsets

This usually is a set of one to five chips that contains all motherboard circuits except theprocessor and memory (in most systems). Because it contains all the main circuits, the chipset

is considered the motherboard. The chipset contains the processor bus interface (called front-side bus, or FSB), memory controllers, bus controllers, I/O controllers, and more. All thecircuits of the motherboard are contained within the chipset.

To understand how important chipsets are, we liken it to a car!The chipset is the frame, suspension, steering, wheels and tires, transmission, drive shaft,

differential, and brakes. The chassis in a car is what gets the power to the ground, allowing thevehicle to start, stop, and corner. Likewise, in the PC, the chipset represents the connection

between the processor and everything else. The processor cant talk to the memory, adapterboards, devices, and so on without going through the chipset. The chipset is the main hub andcentral nervous system of the PC. Therefore if the processor is the brain, the chipset is thespine and central nervous system

Because the chipset controls the interface or connections between the processor andeverything else, the chipset thus dictates which type of processor a motherboard should have;

how fast it will run; how fast the buses will run; the speed, type, and amount of memory that

can be used, and more. In fact, the chipset might be the single most important component in acomputer system, possibly even more important than the processor because it dictates all the

performance parameter and limitations of the board.

Figure:Socket 478 (Pentium 4) showing pin 1 location


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North/South Bridge Architecture

Most of the desktop Pentium chipsets designs, feature a three-chip chipset that supports a

combination PCI/ISA bus architecture. This architecture incorporating what are referred to as

Northand South Bridgecomponents, as well as a Super I/O chip:

.

The North Bridge;So named because it is the connection between the high-speed processor

bus and the slower AGP and PCI buses.

The North Bridge is sometimes referred to as the PAC (PCI/AGP Controller). It is essentiallythe main component of the motherboard and is the only motherboard circuit besides the

processor that normally runs at full motherboard (processor bus) speed. Most modernchipsets use a single-chip North Bridge; however, some of the older ones actually consisted

of up to three individual chips to make up the complete North Bridge circuit.

The South Bridge; So named because it is the bridge between the PCI bus and the evenslower ISA bus(if present). It also typically contains dual ATA/IDE hard disk controller

interfaces; one or more USB interfaces, and in later designs even the CMOS RAM and real-time clock functions. In older designs, the South Bridge contained all the components thatmake up the ISA bus, including the interrupt and DMA controllers.

The Super I/O chip;is connected to the ISA bus or the low pin count (LPC) bus and contains

all the standard peripherals that are built in to a motherboard. For example, most Super

I/O chips contain the serial ports, parallel port, floppy controller, and keyboard/mouseinterface. Optionally, they might contain the CMOS RAM/Clock, IDE controllers, and gameport interface as well. Note however that systems that integrate IEEE 1394 and SCSI ports

use separate chips for these port types.

Figure:A generic chipset arrangement for the North/South bridge architecture system board

Processor

DIMM 1

DIMM 2

PCISlots IDE

SlotsISA Slot

M I/O


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Hub Architecture

The newer 800 series chips from Intel use hub architectures in which the former NorthBridge chip is now called a Memory Controller Hub (MCH) and the former South Bridge is

called an I/O Controller Hub (ICH). Rather than connect them through the PCI bus as in astandard North/South Bridge design, they are connected via a dedicated hub interface that

is twice as fast as PCI.

The MCH interfaces between the high-speed processor bus and the hub interface, and AGPbus whereas the ICH interfaces between the hub interface and the ATA (IDE) ports, theSATA ports on the ICH5, and the PCI bus.

The hub design offers several advantages over the conventional North/South Bridgedesign:

i.

Reduced PCI loading: This hub interface design allows for a much greater throughputfor PCI devices because there is no South Bridge chip (also carrying traffic from theSuper I/O chip) hogging the PCI bus. Due to bypassing PCI, hub architecture also

enables greater throughput for devices directly connected to the I/O Controller Hub(formerly the South Bridge), such as the higher-speed ATA-100, Serial ATA, and USB

2.0 interfaces.

ii. Reduced board wiring: The hub interface design is also very economical, being only 8bits wide. Although this seems too narrow to be useful, there is a reason for the design.

By making the interface only 8 bits wide, it uses only 15 signals, compared to the 64

signals required by the 32-bit-wide PCI bus interface used by North/South Bridge chipdesigns. The lower pin count means less circuit routing exists on the board, less signal

noise and jitter occur, and the chips themselves have many fewer pins, making themsmaller and more economical to produce.

iii. It is faster: Although it transfers only 8 bits at a time, the hub interface executes fourtransfers per cycle and cycles at 66MHz. This gives it an effective throughput of466MHz1 byte = 266MB per second (MBps). This is twice the bandwidth of PCI,

which is 32 bits wide but runs only one transfer per 33MHz cycles for a totalbandwidth of 133MBps. So, by virtue of a very narrowbut very fast design, the hubinterface achieves high performance with less cost and more signal integrity than with

the previous North/South Bridge design.

c. Motherboard BIOS (ROM-BIOS chip)

All motherboards must have a special chip containing software called ROM-BIOS chip. This

ROM chip contains the startup programs and drivers used to get the system running and actas the interface to the basic hardware in the system. When you turn on a system, the power on

self test (POST) in the BIOS also tests the major components in the system. Additionally, youcan run a setup program to store system configuration data in the CMOS memory, which is

powered by a battery on the motherboard. This CMOS RAM is often called NVRAM

(nonvolatile RAM) because it runs on about 1 millionth of an amp of electrical current and canstore data for years when powered by a tiny lithium battery.


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The BIOS is a collection of programs embedded in one or more chips, depending on the designof your computer. That collection of programs is the first thing loaded when you start your

computer, even before the operating system. Simply put, the BIOS in most PCs has four mainfunctions:

i. POST (power on self test). The POST tests your computers processor, memory, chipset,

video adapter, disk controllers, disk drives, keyboard, and other crucial components.

ii. Setup. The system configuration and setup program is usually a menu-driven programactivated by pressing a special key during the POST, and it enables you to configure themotherboard and chipset settings along with the date and time, passwords, disk drives,

and other basic system settings. You also can control the power-management settings andboot-drive sequence from the BIOS Setup, and on some systems, you can also configureCPU timing and clock-multiplier settings. Some older 286 and 386 systems did not have

the Setup program in ROM and required that you boot from a special setup disk, and some

newer systems use a Windows-based application to access BIOS Setup settings.

iii. Bootstrap loader. A routine that reads the first physical sector of various disk driveslooking for a valid master boot record (MBR). If one meeting certain minimum criteria

(ending in the signature bytes 55AAh) is found, the code within is executed. The MBR

program code then continues the boot process by reading the first physical sector of thebootable volume, which is the start of the volume boot record (VBR). The VBR then loads

the first operating system startup file, which is usually IO.SYS (DOS/Windows 9x/Me) or

NTLDR (Windows NT/2000/XP), upon which the operating system is then in control andcontinues the boot process.

iv.

Basic device drivers. BIOS acts as a collection of actual device drivers used to act as a basicinterface between the operating system and the hardware when the system is booted and

running. When the computer is running DOS or Windows in safe mode, it is basicallyrunning almost solely on ROM based BIOS drivers because at this time, none are loadedfrom disk.

Upgrading the BIOS

The ROM BIOS provides the crude brains that get the computers components workingtogether. A simple BIOS upgrade can often give the computer better performance and more

features.

The BIOS is the reason various operating systems can operate on virtually any PC-compatiblesystem despite hardware differences. Because the drivers in the BIOS communicate with the

hardware, the BIOS must be specific to the hardware and match it completely. In other words,always get BIOS upgrades from motherboard manufacturer or from a BIOS upgrade companythat supports the motherboard you have, rather than directly from the BIOS developer.

It should be noted that instead of creating their own BIOS, many computer makers buy a BIOS from

specialists such as American Megatrends, Inc. (AMI) or Phoenix Technologies Ltd. A motherboard

manufacturer that wants to license BIOS must tailor the BIOS code to the hardware. This is what makes

upgrading BIOS somewhat problematic; BIOS usually resides on ROM chips on the motherboard and is

specific to that motherboard model or revision.


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To install some of the larger and faster Integrated Drive Electronics (IDE) hard drives and LS-

120 (120MB) floppy drives in older machines, for example, you might need a BIOS upgrade.Some of the machines you have might be equipped with older BIOSs that do not support hard

drives larger than 8GB, for example.

The following list shows some of the primary functions of a ROM BIOS upgrade; the exactfeatures and benefits of a particular BIOS upgrade depend on a particular system:

Added support for newer-type and faster-speed processors

Support for bootable ATAPI CD-ROM drives (called the El Torito specification)

Support for bootable LS-120 (120MB) SuperDisk floppy or Iomega Zip drive support

Support for bootable USB drives

Fast POST for decreasing boot times

Support for Ultra-DMA/100 or Ultra-DMA/133 ATA drives

Support for ATA hard drives greater than 8.4GB or 137GB (48-bit LBA)

Support for Serial ATA (SATA) drives

Support for a preboot environment and recovery software in the host protected area

(HPA)

Plug and Play (PnP) support and compatibility

Correction of calendar-related and leap-year bugs

Correction of known bugs or compatibility problems with certain hardware and

application or operating system software

Support for ACPI power management

Support for temperature monitoring and fan speed monitoring and control

Support for legacy USB devices (keyboards and mice) Support for chassis intrusion detection

Part of the PC 2001 standard published by Intel and Microsoft requires something called FastPOST to be supported. Fast POST means that the time it takes from turning on the power untilthe system starts booting from disk must be 12 seconds or less (for systems not using SCSI as

the primary storage connection). This time limit includes the initialization of the keyboard,video card, and ATA bus. For systems containing adapters with onboard ROMs, an additional 4seconds are allowed per ROM. Intel calls the Fast POST feature Rapid BIOS Boot (RBB), and it

is supported in all its motherboards from 2001 and beyondsome of which can begin booting

from power-on in as little as 6 seconds or less.

If you install newer hardware or software and follow all the instructions properly, but youcant get it to work, specific problems might exist with the BIOS that an upgrade can fix. This is

especially true for newer operating systems. Many systems need to have a BIOS update to

properly work with the Plug and Play features of Windows 9x, Me, XP, and 2000. Becausethese problems are random and vary from board to board, it pays to periodically check theboard manufacturers Web site to see

whether any updates are posted and what problems they fix. Because new hardware andsoftware that are not compatible with your system could cause it to fail, I recommend youcheck the BIOS upgrades available for your system before you install new hardware or

software, particularly processors.


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Determining a computers BIOS Version

When seeking a BIOS upgrade for a particular motherboard (or system), you need to know thefollowing information:

The make and model of the motherboard (or system)

The version of the existing BIOS

The type of CPU (for example, Pentium MMX, AMD K6, Cyrix/IBM 6x86MX, MII,

Pentium II, Pentium III and later, AMD Athlon, Athlon XP, and so on)

You usually can identify the BIOS you have by watching the screen when the system is firstpowered up. It helps to turn on the monitor first because some take a few seconds to warm up

and the BIOS information is often displayed for only a few seconds.

Factors to consider when choosing a motherboard for your computer

i. Form factor

The first consideration when installing or replacing a system board is whether it willphysically fit and work with the other system components. Hence, the motherboards form

factor, its case style, and its power-supply connection type are important considerations.

Standard PC, PC-XT, and Baby AT boards share the same mounting- hole patterns and can be

exchanged freely with each other. However, the original PC-AT and ATX motherboards have

different mounting-hole pattern specifications. In addition to the mounting hole alignmentissue, the case openings for expansion slots and port connections must be compatible with

those of the motherboard. Various types of keyboard connectors have been used in differenttypes of systems. The most common connectors used with PC keyboards are 6-pin PS/2 mini

DINs, 5-pin DINs, and RJ-11 jacks.Historically, PC-XT- and AT-compatible systems use the 5-pin

DIN connector, whereas the 6-pin mini DIN is used with ATX systems

ii. Processor support

iii. Chipsets

Aside from the processor, the main component on a motherboard is called the chipset. The

chipset contains all the motherboard circuitry except the processor and memory in most

systems and therefore has a profound effect on the performance of the board by dictating allthe performance parameters and limitations of the board, such as memory size and speed,processor types and speeds, supported buses and their speeds, and more.

Although, however, the selection of a chipset must be based largely on the processor and theadditional components intended to be install in the computer, when choosing a chipset, one

should check for the following supported features to ensure they match his/her needs and

desires:


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CPU bus speed support

The type of main memory supported

AGP4X/8X or PCI Express video support

Parallel or Serial ATA interfaces

USB 2.0 (high-speed USB) or FireWire support Support for the fastest available processor in the processor family you choose, even if

you are installing a slower model

iv. BIOS

Another important feature on the motherboard is the basic input/output system (BIOS).

BIOS with support for the Plug and Play (PnP) specification makes installing new cards,

especially PnP cards, much easier. PnP automates the installation and uses special softwarebuilt into the BIOS and the operating system (such as Windows 9x/Me and Windows2000/XP) to automatically configure adapter cards and resolve adapter resource conflicts.

Several import things to consider here are.

i. BIOS support; both the processor to install initially and the processor that might beupgraded to in the future. If the motherboard and chipset can handle a new processor

but the BIOS cannot, a BIOS upgrade can be used to provide proper support.

ii. BIOS is supplied by one of the major BIOS manufacturers, such as AMI (AmericanMegatrends International), Phoenix, or Award (owned by Phoenix).

iii. BIOS is contained in a special type of reprogrammable chip called a Flash ROM or

EEPROM (electrically erasable programmable read-only memory). This enablesdownloading BIOS updates from the manufacturer and, using a program it supplies,

easily updates the code in your BIOS. If the motherboard does not have the Flash ROMor EEPROM type, then the chip must physically be replaced if an update is required

v. Memory

Main memory for modern PCs typically is installed in the form of dual inline memory modules(DIMMs). These models are of several variationsThings to consider here are

i. Number of DIMMs required to make a single bank of memory, and the slots/sockest

your motherboard have.

ii.

Error correction code (ECC). Memory modules can include an extra bit for each 8 forparity checking or ECC use. If ECC is important to you, be sure your chipset (andmotherboard) supports ECC before purchasing the more expensive ECC modules.

iii. The type of metal on the memory module contacts, especially on motherboards using

SIMMs. SIMMs were widely available with either tin- or gold-plated contacts. The typeof plating on the module contact should always match the type to what is also used onthe socket contacts. In other words, if the motherboard sockets have tin-plated

contacts, then modules with tin-plated contacts must be used and likewise must matchgold to gold. If you mix dissimilar metals (tin with gold), corrosion on the tin side israpidly accelerated and tiny electrical currents are generated. The combination of the

corrosion and tiny currents causes havoc, and several types of memory problems anderrors can occur


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vi. I/O Ports

Although most motherboards today have built-in I/O ports, all ports needed may not be

included. Therefore, a motherboard should include at least the following I/O ports:

i.

PS/2 Keyboard connector (mini-DIN type)ii. PS/2 Mouse port (mini-DIN type)

iii. One or two serial portsiv. Parallel port

v. Four or more USB portsvi. Two or more FireWire ports

vii. Analog VGA or DVI video connector (integrated video)

viii. RJ-45 port for 10/100 or 10/100/1000 Ethernetix. Audio/game connectors (speaker, microphone, and MIDI/joystick)x. Two or more parallel ATA ports

xi. Two or more serial ATA ports

xii.

Floppy controller connector

vii. Power supply

Power-supply size, orientation, and connectors present another compatibility consideration.For example, an AT power supply cannot be installed in an ATX case. Because the AT boltpattern is different from the ATX bolt pattern, it cannot be properly secured and grounded in

the ATX case. Also, the single power connector from the ATX power supply will not connect toan AT system boards dual (P8/P9) power connector. Finally, true ATX fans are designed toblow air into the case from the rearAT power supplies pull it through the case from the

front

End of this Lecture

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Repair and Maintenance PC System Components