The important constituent components of an ATX Motherboard are given below:

1. Mouse & keyboard 2. USB

3. Parallel port 4. CPU Chip 5. RAM slots 6. Floppy controller 7. IDE controller 8. PCI slot 9. ISA slot 10. CMOS Battery 11. AGP slot 12. CPU slot 13. Power supply plug in

1. Mouse & keyboard: Keyboard Connectors are two types basically. All PCs have a Key

board port connected directly to the motherboard. The oldest, but still quite common type,

is a special DIN, and most PCs until recently retained this style connector. The AT-style

keyboard connector is quickly disappearing, being replaced by the smaller mini DIN PS/2-style keyboard connector.

You can use an AT-style keyboard with a PS/2-style socket (or the other way

around) by using a converter. Although the AT connector is unique in PCs, the PS/2-style

mini-DIN is also used in more modern PCs for the mouse. Fortunately , most PCs that use

the mini-DIN for both the keyboard and mouse clearly mark each mini-DIN socket as to its

correct use. Some keyboards have a USB connection, but these are fairly rare compared to

the PS/2 connection keyboards.

2. USB (Universal serial bus):

USB is the General-purpose connection for PC. You can find USB versions of many

different devices, such as mice, keyboards, scanners, cameras, and even printers. a USB connector's distinctive rectangular shape makes it easily recognizable.

USB has a number of features that makes it particularly popular on PCs. First, USB devices are hot swappable. You can insert or remove them without restarting your system.

3. Parallel port: Most printers use a special connector called a parallel port. Parallel port

carry data on more than one wire, as opposed to the serial port, which uses only one wire.

Parallel ports use a 25-pin female DB connector. Parallel ports are directly supported by the motherboard through a direct connection or through a dangle.

4. CPU Chip : The central processing unit, also called the microprocessor performs all the

calculations that take place inside a pc. CPUs come in Variety of shapes and sizes.

Modern CPUs generate a lot of heat and thus require a cooling fan or heat sink. The

cooling device (such as a cooling fan) is removable, although some CPU manufactures sell the CPU with a fan permanently attached.

5. RAM slots: Random-Access Memory (RAM) stores programs and data currently being

used by the CPU. RAM is measured in units called bytes. RAM has been packaged in many

different ways. The most current package is called a 168-pin DIMM (Dual Inline Memory module).

6. Floppy controller: The floppy drive connects to the computer via a 34-pin ribbon

cable, which in turn connects to the motherboard. Afloppy controller is one that is used to

control the floppy drive.

7. IDE controller: Industry standards define two common types of hard drives: EIDE and

SCSI. Majority of the PCs use EIDE drives. SCSI drives show up in high end PCs such as

network servers or graphical workstations. The EIDE drive connects to the hard drive via a

2-inch-wide, 40-pin ribbon cable, which in turn connects to the motherboard. IDE

controller is responsible for controlling the hard drive.

8. PCI slot: Intel introduced the Peripheral component interconnect bus protocol. The

PCI bus is used to connect I/O devices (such as NIC or RAID controllers) to the main logic of the computer. PCI bus has replaced the ISA bus.

9. ISA slot: (Industry Standard Architecture) It is the standard architecture of the Expansion bus. Motherboard may contain some slots to connect ISA compatible cards.

10. CMOS Battery: To provide CMOS with the power when the computer is turned off all

motherboards comes with a battery. These batteries mount on the motherboard in one of

three ways: the obsolete external battery, the most common onboard battery, and built-in

battery.

11. AGP slot: If you have a modern motherboard, you will almost certainly notice a

single connector that looks like a PCI slot, but is slightly shorter and usually brown. You

also probably have a video card inserted into this slot. This is an Advanced Graphics Port

(AGP)slot

12. CPU slot: To install the CPU, just slide it straight down into the slot. Special notches

in the slot make it impossible to install them incorrectly. So remember if it does not go

easily, it is probably not correct. Be sure to plug in the CPU fan's power.

13. Power supply plug in:

The Power supply, as its name implies, provides the necessary electrical power to make

the pc operate. the power supply takes standard 110-V AC power and converts into +/-

12-Volt, +/-5-Volt, and 3.3-Volt DC power.

The power supply connector has 20-pins, and the connector can go in only one direction.

BIOS Firmware

BIOS stands for Basic Input/Output System. It contains basic instructions to interact with various

hardware modules such as Motherboard controllers or that of interface cards. BIOS is the

software that is run by a computer when first powered on.

A computer motherboard inevitably contains a BIOS chip in the form of an onboard PROM,

EPROM or flash memory. When the computer is powered on, it performs diagnostic tests on the

computer hardware devices such as hard drive, FDD, and memory. It searches for other BIOS's

on the plug-in boards, and takes care of them. It then loads the operating system and passes

control to OS. The BIOS accepts requests from the drivers as well as the applications as shown

in the figure below.

BIOS is also known as PC firmware because it is an integral part of the motherboard.

Firmware on adapter cards: A computer can contain several BIOS firmware chips.

The motherboard BIOS is normally used to access basic hardware components such as

the keyboard, floppy drives, and hard disk controllers. Adapter cards such as SCSI,

RAID, and video boards may include their own BIOS software.

Firmware generally available in different forms:

1. EPROM (Erasable Programmable ROM), for updating a BIOS firm using EPROM,

you may need to get a new chip from the manufacturer.

2. EEPROM (Electrically Erasable Programmable ROM), you can update a BIOS

firmware using EEPROM using "boot to floppy", and running the Firmware update

program.

3. Flash ROM - faster at rewriting the chip

A typical BIOS chip used on motherboards is shown in the figure below. Though it is

a square-type PLCC package, BIOS chips come in different forms. Figure 2 shows the

BIOS after insertion into the socket.:

BIOS chip BIOS chip after insertion into a socket.

Memory:

PC memory stores data and programs currently being executed by the computer. It is important

that the information is fetched by the CPU quickly to further processing. There are several

memory types available. Important among there include the following:

Dynamic RAM (DRAM) Synchronous RAM (SRAM) Synchronous DRAM (SDRAM) Rambus DRAM (RDRAM) Video RAM (VRAM) Windows RAM (WRAM) EDO RAM

RAM stands for Ramdom Access Memory.

Dynamic RAM (DRAM): In dynamic RAM, the RAM gets refreshed continually by

the controller. DRAM has been introduced in the earlier stages, and RAM versions

available today are much bigger and faster than the earlier simple DRAMs.

DRAMs store data in the form of capacitive charges. Since any capacitor tends to be

leaky, a DRAM needs to be refreshed on a continual basis.

Synchronous RAM (SRAM): SRAM contains a clock built onto the memory module,

enabling the SRAM to be in synchronization with the motherboard cloak. SDRAM

doesn't require frequent recharge like DRAM. L-2 memory caches are usually made

of SRAM and exhibit very fast read and write operations.

Synchronous DRAM (SDRAM): SDRAM works in sync with the motherboard, and

hence works quite fast. SDRAMs have speeds of the order of 133MHz, 800MHz, etc.

Rambus DRAM (RDRAM): RDRAM technology was developed originally by

Rambus, Inc. Rambus memory is integrated onto Rambus Inline Memory Modules

(RIMMs). RDRAM chips are synchronized to the processor's memory bus.

Comparison Chart:

Memory

Type Synchronization

DRAM CPU synchronized to the motherboard. DRAM is neither synchronized to

the motherboard nor CPU.

SRAM CPU and memory module are synchronized to the motherboard.

RDRAM

Synchronizes to the memory bus clock. Memory bus clock is much faster

than the motherboard clock. Hence faster data transfer between the

CPU and the memory module occurs.

Video RAM (VRAM): VRAM is primarily used on video cards. It is dual ported, in

the sense that while one device write to VRAM, another device can simultaneously do

read operation. This is quite useful in animation and other speed sensitive video

applications. VRAMs are more expensive than DRAMs, but provide better graphic

display. Windows RAM (WRAM) is another type of memory used for graphics, and

is similar to VRAM in functionality. However, with the faster memory access

schemes like DDR, VRAM and WRAM are slowly becoming obsolete.

Double Data Rate SDRAM (DDR SDRAM):

DDR SDRAM is similar to SDRAM, but for the difference that DDR reads data on

both the rising and falling edges of the clock. SDRAM reads only on the rising edge

of a signal. This technique allows the DDR module to achieve speeds twice that of

SDRAM. For example, instead of a data rate of 133MHz, DDR memory transfers data

at 266MHz.

Memory Modules:

Memory modules are printed circuit cards made up of memory chips, and a few other

passive components. Normally, memory modules are the those that get installed on

the motherboard, and you don't handle individual memory chips. The following are

the prominently used memory modules (also called memory cards):

Dual In-line Package (DIP) Single In-line Memory Modules (SIMM) Dual In-line Memory Modules (DIMM) Rambus In-line Memory Modules (RIMM) DDR DDR II

Dual In-line Package (DIP): Initially, PC XT, and AT systems came with DIP sockets.

Individual memory chips were inserted into the sockets.

DIP chip DIP socket

A typical DIP socket, and chip are shown in the figure above. As can be seen, there is

only one chip per DIP package. This arrangement resulted in several DIP sockets

being present on the motherboard. If you need to enhance the memory, buy additional

chips and insert into any existing DIP sockets. There are several disadvantages

because of this method:

1. Due to size, these chips used to take lot of space, 2. The chips used to dislodge from respective sockets, and give raise to errors 3. It is cumbersome to insert individual chips 4. Used to take more power

Because of the above problems, memory chips were integrated into SIMM (Single In-

line Memory Modules) that overcome several of the said problems.

Single In-line Memory Modules (SIMM):

SIMM modules have several memory chips soldered in-line on its own circuit board.

A typical SIMM is shown in the figure below. There are two types of SIMM modules:

30-pin SIMM modules, and 72-pin SIMM modules. Typically, a 72-pin SIMM has

32-bit wide memory bus, whereas a DIMM has 64-bit wide memory bus. On a SIMM,

the edge connector pins on either side of a SIMM are shorted, representing only one

signal pin.

Typical SIMM package:

Memory Size:64MB

Memory Speed: 60nS

Pins: 72

Dual In-Line Memory Modules (DIMM):

DIMMs are very similar to SIMMs. The major difference is that a DIMM has two

different signal pins on each side of the module as shown in the figure. One big

advantage of DIMM is that only one module can be inserted into the motherboard,

whereas you need two SIMMs (paired) when working with 64-bit microprocessors

like Pentium II and above. Since SIMM provides only 32-bit bus, you need to use 2-

SIMMs paired together with any modern 64-bit processor.

Typical DIMM package

(using DDRAM):

Memory size: 256MB

Pins:168 pin

SIMMs typically have 72 pins, whereas DIMM have 168 pins.

Rambus In-Line Memory Module (RIMM):

Rambus inline memory modules (RIMMs) use Rambus Dyamic RAM (RDRAM)

chips.

A RIMM package using RDRAM

Double Data Rate:

DDR modules are also called DIMMs (Dual-In-Line-Memory Module). A typical

DDR module (DIMM) is shown above. The DIMM package using DDR is twice as

fast as the one using SDRAM.

Memory Size: 2X512MB

Memory Speed: 400MHzPC3200

Memory Type: Dual Channel DDR

Pins: 184

Socket 478:

Socket 478 is a PGA socket used by Intel Pentium 4 microprocessor family (not all P

IV family processors support Socket 478)..

Socket type: Socket 478 (mPGA478B)

Front Bus Frequencies: 400 MHz - 800 MHz (100 MHz - 200 MHz QDR)

Socket size: 1.38" x 1.38" (3.5 x 3.5 cm)

Number of contacts: 478

Compatible package types:

478-pin micro FC-PGA

478-pin micro FC-PGA2

Compatible processors:

Processors Intel Pentium 4 (1.4 - 3.4 GHz)

Intel Celeron (1.7 - 3.2 GHz)

Celeron D (to 3.2 GHz)

Intel Pentium 4 Extreme Edition (3.2, 3.4 GHz)

This socket has currently been replaced with socket 775.

Socket 423:

The socket was used for low-end Pentium IV processors below 2000MHz frequencies.

It became obsolete with the advent of Socket 478.

Number of Contacts: 423

Compatible package type: Organic Land Grid Array (OLGA)

Front Bus Speed: 100 MHz FSB

Compatible Processors: Intel Pentium 4 (1300 MHz - 2000 MHz)

Socket 370:

Socket 370 (PGA370) is a PGA socket compatible with Intel Celeron and Pentium III

processors in Pin Grid Array (PGA) package.

Socket 370 Processor package

Salient Features:

Compatible package types:

370-pin Plastic Pin Grid Array (PPGA); 370-pin Flip-Chip Pin Grid Array (FC-PGA)

370-pin Flip-Chip Pin Grid Array (FC-PGA2)

Number of contacts: 370

Front Bus Frequencies: 66, 100 and 133 MHz

Supported Processors include the following:

Intel Celeron (PPGA, 300–533 MHz)

Intel Celeron (FC-PGA, 533–1100 MHz)

Intel Celeron (FC-PGA2, 900–1400 MHz)

Intel Pentium III (FC-PGA, 500–1133 MHz)

Intel Pentium III Tualatin (FC-PGA2)

Celeron Tualatin (FC-PGA2)

VIA C3 (FC-PGA)

Socket 8:

Socket 8 was used for a very limited number of processor types. The socket is being

no more used by newer processors.

Number of Contacts: 387

Front Bus Speed : 66-75 MHz

Supported Processors include the following:

Pentium Pro 150~200, Pentium II OverDrive 300~333

Socket 7:

Socket 7 was introduced by Intel for Pentium 133 - 200 MHz processors. It is also

used in Pentium MMX processor family.

Socket 7 Compatible Processor

Salient Features:

Compatible package types:

296-pin staggered Plastic Pin Grid Array (PPGA)

296-pin staggered Ceramic Pin Grid Array (CPGA or SPGA)

296-pin Flip-Chip staggered Ceramic Pin Grid Array

321-pin ceramic Ping Grid Array (CPGA)

Number of contacts: 321

Front Bus Frequencies: 66 - 83 Mhz System Clock

Supported Processors include the following:

AMD K5 (75 MHz - 200 MHz); AMD K6 (166 MHz - 300 MHz)

AMD K6-2 (200 MHz - 570 MHz)

AMD K6-III (333 MHz - 550 MHz)

Cyrix 6x86, 6x86L and 6x86MX (90 MHz - 266 MHz)

Cyrix MII (233 MHz - 433 MHz)

Intel Pentium (non-MMX) (75 MHz - 200 MHz)

Intel Pentium MMX (166 MHz - 233 MHz)

Socket A (Socket 462):

Socket A (also called Socket 462) is a PGA socket compatible with AMD K7 family

of processors.

Socket A Processor for Socket A

Bus Frequencies: 100 MHz, 133 MHz, 166 MHz and 200 MHz

Number of contact pins: 462 pin holes

Compatible Processors include the following:

AMD Athlon (650 MHz - 1400 MHz)

AMD Athlon XP (1500+ - 3300+)

AMD Duron (600 MHz - 1800 MHz)

AMD Sempron (2000+ - 3300+)

AMD Athlon MP (1000 MHz - 3000+)

Compatible package types:

462-pin ceramic Pin Grid Array (PGA) package, 462-pin organic PGA.

Slot A:

Slot A is used by AMD's Athlon family of processors. It has 242 contacts, physically

similar to that of Intel's Slot 1. But Slot A is electrically different from that of Slot 1.

Slot 2:

Slot 2 is a 330 contact version of Slot 1. Intel's Xeon processor uses Slot 2. The Slot 2

cartridge may house as many as four processors and an L2 cache.

Slot 1:

Slot 1 is a Slot-type connector. This connector is compatible with Pentium II family of

processors, and some of low-end Celeron processors. Pentium III was the last

microprocessor family that used the Slot 1.

Pentium IV family of processors do not use Slot 1.

Number of Contacts: 242

Processors types supported include the following:

Intel Celeron (SECC, 233-466 MHz)

Processors Intel Pentium II (SECC, 233-450 MHz)

Intel Pentium III (SECC2, 450-1133 MHz)

Compatible package types:

Single Edge Processor Package (SEPP)

Single Edge Connector Cartridge (SECC)

Single Edge Connector Cartridge 2 (SECC 2)

1. Floppy Disk Drive (FDD):

A Floppy Disk Drive is a disk drive that enables a user to save data to removable

disk. Initially, FDDs used the 5 1/4" floppy disks, which were later replaced with 3

1/2" disks. However, with the advent of removable hard disks, and flash drives, many

computers no longer use floppy disk drives.

The Pentium motherboard provides a standard 34-pin connector for interfacing with

FDD. A 34-pin flat ribbon cable is used to connect the motherboard to FDD. This

cable connects the motherboard's FDD interface with one or two floppy disk drives.

Floppy Disk Controller (FDC) uses I/O address range 370 to 37Fh. FDD divides the

floppy disk into 80 tracks per side, with 9 or 18 512-byte sectors per side. This

provides the system with 720KB ( 737,280 bytes) or 1.44MB (1,474,560 bytes) of

storage. For power supply, FDD uses a Berg connector as illustrated in the figure

below.

The FDD controller is assigned the IRQ-6 in PC-compatible systems. The FDD

controller generates an interrupt signal each time it receives a Read, Write, or Format

command from the system.

3.5" Floppy Disk Drive. Connector side of the FDD

Yellow wire: +12V

Red wire: +5V

Black wires: Ground.

Berg Connector

Floppy Drive Interface Cable:

The FDD interface cable is used to connect the FDD to the motherboard.

Figure: A Five connector Floppy Interface Cable

The FDD cable in the figure shows traditional five connectors configuration. It has

connectors for 5.25" drives, as well as 3.5" drives, and 34-pin wide. However, 5.25"

drives are rarely used now-a-days. "Cable Twist" in the floppy cable is located

between the two pairs of connectors intended "A" and "B" floppy drives. This twist

causes the drive at the end of the cable to appear as A: to the system and the one in the

middle to be as B:.

Cathode Ray Tube (CRT):

CRT display is the most commonly used form of visual displays, through it is getting

gradually replaced with LCD and Plasma displays.

A computer monitor using CRT display.

In a CRT, an electron beam sweeps the display screen horizontally, one line at a time,

gradually down the screen. A synchronization (sync) signal brings the beam back to

the top row of the display. This type of scanning (line-by-line) is known as raster

scan.

Figure: CRT cross sectional diagram showing important components of a CRT.

There are two types of cathode ray displays. One is non-interlaced, and the other is

interlaced. Normally, all the displays are interlaced to reduce flicker.

As shown in the figure, for non-interlaced display, the scanning is done continuously

from top to bottom. For non-interlaced display, alternate rows are scanned.

A black and white monitor contains only one electron gun, whereas a color display

monitor will have three electron guns, each of which represent red, green, and blue.

The horizontal and vertical deflection takes place by applying appropriate voltages to

the horizontal, and vertical deflection plates. Usually, the screen is refreshed between

60-100 times per second.

The grid shown in the figure controls the speed with with the electrons hit the screen.

If a positive voltage is applied to the screen grid, because of which the electrons are

accelerated and hit the screen, making the screen brighter. If a negative voltage is

applied to the grip, the electrons are decelerated and the screen will not glow. The

microscopic control of electron beam flow, produces images on the screen.

One basic unit of measurement is "pixel". A pixel is the smallest area in a graphics

display that can be manipulated.

Given below are the commonly used screen resolutions:

Display Type Number of pixels

Video Graphics Array

(VGA) 640 * 480 pixels

Super Video Graphics

Array(SVGA) 800 * 600 pixels

eXtended Graphics

Array (XGA) 1024 * 768 pixels

Super eXtended

graphics Array (SXGA) 1280 * 1024 pixels

Screen resolution is always stated as the horizontal number of pixels by the vertical

number of pixels. A screen displaying 800 x 600 pixels has 600 rows, each 800 pixels

wide.

Graphics Cards: The graphics card resides in the CPU box, and drives the video

display. A typical graphics card is shown below:

The graphics card shown includes DVI connector, TV/Video connector, and a VGA

connector. The card has an on-board graphics processor with cooling fan. Usually, for

graphic intensive applications, you need a higher end graphic adapter card. For normal

desktop usage, a video adapter will be sufficient.

PCM CIA Interface Cards (PC Cards)

PCMCIA stands for Personal Computer Memory Card International Association. PCMCIA

standards were developed for small, credit card-sized devices, called PC Cards. Though

PCMCIA cards (PC Cards) were originally developed for use with Notebook computers, the

same are being extensively used in other devices also.

Types of PC Cards:

There are 3 types of PC Cards.

1. Type-I

2. Type-II

3. Type-III

1. Type-I PC Cards are typically used for memory devices such as RAM, Flash, and SRAM

cards.

2. Type II PC Cards are typically used for I/O devices such as modems, and LAN cards.

3. Type III PC Cards are used for devices that consist of thicker components, such as rotating

mass storage devices.

Important characteristics of PC Cards:

Property Value

Physical Interface

Connector 68 pins

Length 85.6 mm

Width 54.0 mm

Thickness

Type-I 3.3 mm

Type-II 5.0 mm

Type-III 10.5 mm

Back-end I/O Connector Depends on the functionality of the PC

Card

PCMCIA Card (PC Card) slots:

Just like PC Cards, PCMCIA slots also come in three sizes:

Type I slot: Holds up to one Type I card

Type II slot: Holds up to one Type II card or two Type I cards

Type III slot: Holds up to one Type III card or a Type I and Type II card.

Advantages of PC Cards:

Several advantages offered by PC cards are as given below:

1. CardBus: CardBus allows PC Cards and hosts to use 32-bit bus mastering.

2. DMA: The Standard allows cards to utilize Direct Memory Access technology

directly in the hardware when matched with a corresponding host system.

3. eXecute In Place (XIP): XIP allows operating system and application software to

run directly from the PC Card. This in turn improves performance, and eliminates the

need for large amounts of system RAM.

4. Low Voltage Operation: The Standard enables 3.3V as well as 5V operation.

6. Plug and Play: PC Cards can be inserted or removed while the system is powered-

on.

7. Power Management: The Standard provides a means to interface to APM

(Advanced Power Management).

PC Card Uses:

Some of the frequently used PC Card types include the following:

LAN card Wireless LAN card Modem card ATA flash disk card IEEE 1394/Firewire USB

A wireless LAN serves the same functionality of a traditional LAN card, but operates

without being physically wired to a network device. It enables a mobile user to

connect to a local area network (LAN) through a wireless connection. IEEE 802.11a,

802.11b, and 802.11g specify the technologies for wireless LANs.

Linksys 802.11b/g Wireless PC Card

A wireless LAN card is shown in the figure above. Typical specifications for the same

are given below:

Connection Type: Wireless

Connector: PCMCIA

Supported Wireless Standards: 802.11b, 802.11g

Supported Operating Systems: Windows, 98, ME, 2000, XP

IRQs, and I/O Addresses:

IRQ ( Short for Interrupt ReQuest):

An IRQ allows a device to request certain system resources on priority. Normally, the system allowcates the different non-competing IRQ numbers

to different devices. The system allocated IRQs may some times be manually changed. However, it may lead to serious IRQ conflicts resulting in a

hung operating system.

The table below gives normally assigned IRQ numbers in Pentium compatible systems

:IRQ Usage Comments

0 System Timer This IRQ is used within the system board for system timing.

1 Keyboard Controller This IRQ is assigned to the keyboard. Not available to any other

add-in cards.

2 Tied to IRQs 8-15 This IRQ was assigned to older EGA video cards.

3 COM2 This IRQ is assigned to the serial ports COM 2, and COM 4.

Avoid setting this IRQ to other devices.

4 COM1 This IRQ is assigned to the serial ports COM 1, and COM 3.

Avoid setting this IRQ to other devices.

5 LPT2 or Sound Card This IRQ is assigned to a secondary printer port LPT2. If LPT2 is

not available, it is used for sound card.

6 Floppy Diskette Controller

This IRQ is assigned to the Floppy Diskette Controller. Since

most systems use FDC, do not use this IRQ for other

requirements.

7 LPT1

This IRQ is assigned to the parallel port LPT1. It can also be

made available to other add-in cards, but avoid using it for any

other cards. It may lead to conflicts at a future time, when you

least anticipate it.

8 Real Time Clock This IRQ is reserved for the internal real-time clock. This line is

NOT available to other add-on cards.

9 Substitutes for IRQ 2 This IRQ uses IRQ 2 to talk to the CPU. Normally used for

network cards.

10 Not Assigned Can be used for network card, or others

11 Not Assigned Left open for use with any other device

12 PS/2 Mouse Port

This IRQ is used for the PS/2 style mouse port normally

available on many motherboards. If you are using PS/2 Mouse

port on system, do not use this IRQ for anything else.

13 Numerical Processing Unit

(NPU)

Used for math co-processor, and not available for other

devices.

14 Primary Hard Disk

Controller This IRQ is assigned to the primary hard drive interface

15 Secondary Hard Disk

Controller This IRQ is assigned to the secondary hard drive interface.

Memory Mapped Input/Output Addresses:

Input/output addresses ( I/O addresses for short) are resources used by almpst every device in the computer. The I/O addresses represent the location

in memory for a given device to exchange information between itself, and the rest of the system. These address spaces are permanently allocated to

the system devices. If an address space allocated to one device (say, LPT) is assigned to another device (say, IDE controller) than I/O address

conflict will arise, and the system may hang or not function normally.

Given below is the list of commonly used I/O address spaces allocated to various system devices:

I/O

Address Common Device using the Address Space

060h and

064h Used by keyboard controller

130 and

140 Used by SCSI host adapters

170h Secondary IDE Interface

1F0h Primary IDE Interface

220 Default address for Sound cards

240 Optional address for sound cards and network cards

260 and

270 Optional address for sound cards and network cards.

278h Assigned to LPT2 or LPT3

280 Optional address for sound cards and network cards

300 Default for many network cards

2E8h Assigned to COM 4 and used with IRQ 3

2F8h Assigned to COM 2 and used with IRQ 3

300h nother Network Interface Card choice

320h

Used for a SCSI host adapter or MIDI device. You can

use this for a Network card when not assigned to any

SCSI or MIDI device.

330h Used for the SCSI host adapters

340h Could be used for a SCSI host adapter

360h Could be used for a Network card, provided there are

no conflicks.

378h This is assigned to the first parallel printer port (LPT 1)

in color systems. Normally used with IRQ 7.

3BCh This is assigned to the first parallel printer port (LPT1)

in monochrome systems.

3E8h Assigned to COM 3 and used with IRQ 4

3F8h Assigned to COM 1 and used with IRQ 4

A rule of thumb for IEQ, and IO address conflicts is that the PC is unable to boot or giving error codes during boot process. If you have installed any

device recently, remove or disable it and see if the PC boots properly.

Cables and Connectors

Serial Ports:

The serial port is an Asynchronous port which transmits data one bit of data at a time. Serial

port hardware usually consists of a UART (Universal Asynchronous Receiver/Transmitter).

Most commonly used serial ports are given below:

1. DB9:

DB9 adheres to the RS-232c interface standard. It has 9 pins as shown in the figure. The

connector is "D" shaped, and easy to recognize. The function of each pin is described below.

Outline Diagram of DB-9 DB-9 Female Connector

Pin description:

Pin # Pin Description

Pin 1 Data Carrier Detect DCD

Pin 2 Received Data RxData

Pin 3 Transmitted Data TxData

Pin 4 Data Terminal Ready DTR

Pin 5 Signal Ground Gnd

Pin 6 Data Set Ready DSR

Pin 7 Request To Send RTS

Pin 8 Clear To Send CTS

Pin 9 Ring Indicator RI

2. DB25:

DB25 adheres to the RS-232C interface standard. It has 25 pins as shown in the figure. The

connector is "D" shaped, and easy to recognize. DB-25 is normally used in older computers, and

not much used in modern day computers.

DB-25 Male Connector

3. RJ-11:

RJ-11 is a 4-wire connector, commonly used with a modem. It should not be confused with

bigger RJ-45 cable and connector. RJ-45 is commonly used for Ethernet network interface card

(NIC).

Schematic of RJ-11 Connector An RJ-11 Cable with Connector

Pin # Function

A1 Ground

A2 Rx (Data Input)

A3 Tx (Data Output)

A4 Vc (Power)

4. RJ-45:

An RJ-45 connector has 4 pairs of wires as shown in the schematic diagram below. Note that an

RJ-11 is a 4-wire connector, where as RJ-45 is an 8-wire connector.

RJ-45 connector schematic RJ-45 connector crimped to a

cable.

RJ-45 connector is commonly used for Ethernet Networking ports. Devices that

normally use RJ-45 ports include NICs, Hubs, Switches, and Routers.

There are basically two types of cables. One is Straight-through cable, and the other is

Cross-over cable. Straight-through cables are used for connecting a network device to

a work station. Cross-over cables are used for connecting a hub to a switch or a hub to

another hub.

Parallel Ports:

1. DB-25

DB-25 connector is most commonly used in conjunction with a parallel printer. It has

an 8 bit data bus as shown in the figure below.

Pin # Function

Pin 1 Strobe

Pin 2 Data Bit 0

Pin 3 Data Bit 1

Pin 4 Data Bit 2

Pin 5 Data Bit 3

Pin 6 Data Bit 4

Pin 7 Data Bit 5

Pin 8 Data Bit 6

Pin 9 Data Bit 7

Pin 10 Acknowledge

Pin 11 Busy

Pin 12 Paper End

Pin 13 Select

Pin 14 Auto Feed

Pin 15 Error

Pin 16 Initialize Printer

Pin 17 Select Input

Pin 18 - Pin 25 Ground (return for pins 0-7)

The length of Parallel Printer cable usually limited to a maximum of 15 feet

Other Type of Parallel Ports:

Enhanced Parallel Port (EPP): The Enhanced Parallel Port (EPP) operates close to

ISA bus speed and can achieve transfer rates up to 1 to 2MB/sec of data.

Enhanced Capabilities Port (ECP): The Enhanced Capabilities Port (ECP), is an

additional enhanced Parallel port.

Connectors and Cables -ii

1. USB

USB stands for Universal Serial Bus. The most important features of USB bus include the

following:

Plug'n'Play: USB is a truly plug-n-play port. The port is automatically detected by the

system, and its ready to use.

Hot plug and unplug: It is possible to insert an USB device and and unplug without

affecting the functioning of a computer. You dont need to power-off the computer to

remove or insert a USB device.

127 physical devices: A USB can support up to 127 devices. This is much more than

what is normally required.

Low cost cables and connectors

USB connectros can be broadly divided into USB A, and USB B. The difference

between the two is in the physical layout of pins in the connector. Both are shown in

the figure below.

Pin # Function

Pin 1 +5V DC

Pin 2 Data-

Pin 3 Data+

Pin 4 Ground

USB"A" plugs are used towards the host system and USB "B" plugs are used towards

the USB device.

2. FireWire/IEEE1394

FireWire/IEEE1394 port provides data rates up to 400 Mb/sec. The standard is most suitable for

transferring high volumes of information including video, and voice data.

Given below are some of the important features of IEEE 1394 standard:

Based on open licensing system. Digital transmission with data rates of 100, 200, or 400 mega bits per second

(Mb/sec). Plug and play: Automatically detected by the operating system during start-up

or during usage. Hot pluggable: Cables can be connected and disconnected without turning off

power to the computer. Flexible: You can connect FireWire cables in a daisy-chain or in branching cable

configurations. Peer-to-peer functionality Compatibility, lower speed USB devices can be connected with higher speed

devices. Supports both asynchronous (Based on request-and-acknowledge form of

computer communication, used typically with dial-up modems). and isochronous data transfer.( Continuous, guaranteed data transmission at a pre-determined speed. Useful for video and audio).

4 PIN IEEE1394 (without Power)

A IEEE 1394 Connector schematic

Pin Function

Pin #1 Twisted-pair B, differential signals, TPB-

Pin #2 Twisted-pair B, differential signals, TPB+

Pin #3 Twisted-pair A, differential signals, TPA-

Pin #4 Twisted-pair A, differential signals, TPA+

6 PIN IEEE1394 (with Power):

IEEE1394 6-pin connector schematic.

Pin # Function

1 Power, 18-28v no load.

2 Ground

3 Twisted-pair B, differential signals, TPB-

4 Twisted-pair B, differential signals, TPB+

5 Twisted-pair A, differential signals, TPA-

6 Twisted-pair A, differential signals, TPA+

PC Power Supplies

PC power supplies deliver required DC power to the computer electronic sub-

systems including Motherboard, Hard drive, CDROM drive, Keyboard, Mouse, and

others. Usually, regular CRT monitors derive power separately from the mains. PC

power supplies work by converting the AC mains power supply to required DC

power supplies.

There are mainly two types of power supplies used in computers:

ATX Power Supply

ATX12V Power Supply

ATX12V power supplies are intended to be downward compatible with ATX power

supplies.

As the PC components take more and more power, to enable the delivery of more +12

VDC current to the motherboard, additional 4-pins are provided for taking care

of +12 V power supply. Thus, ATX12V will have a +12 V power connector, and a

simple ATX power supply with not have the +12V power connector.

An ATX power supply, typically found in all Pentium class computers is shown

below:

The voltages produced by ATX/ATX12V power supplies are:

1. +3.3 Volts DC 2. +5 Volts DC 3. -5 Volts DC 4. +5 Volts DC Standby 5. +12 Volts DC 6. -12 Volts DC

ATX and ATX12V power supply connectors pin configuration is shown below:

ATX12V Connector (it has 24 pins) ATX Connector (it has 20 pins)

In addition to the Motherboard power connector, a power supply may have a CPU

power connector, and an Auxiliary power connector.

Following are the most commonly used power supply connectors:

4 Pin Berg Connector: Used to connect the PSU to small form factor devices, such as 3.5" floppy drives. Available in: ATX & ATX12V

4 Pin Molex Connector 4 Pin Molex Connector: This is used to power various components, including hard drives and optical drives. Available in: ATX and ATX12V

20 Pin Molex ATX Power Connector: This is used to power the motherboard in ATX systems.available in: ATX (ATX12V have 24 pins)

4 Pin Molex P4 12V Power Connector: Used specifically for Pentium 4 Processor Motherboards. available in: ATX (integrated into the power connector in ATX12V)

6 Pin AUX Connector 6 Pin AUX Connector: Provides +5V DC, and two connections of +3.3V.available in: ATX/ATX12V

To power up an ATX or ATX12V PSU for testing, short pin 14 (PS_ON) with any of

the ground pins.