BCA II Yr/ I Sem
Over view of computer systems:
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Introduction: A computer is an electronic data processing system which accepts the input data, stores the data
and performs the arithmetic and logical computations in rapid speed and outputs the required information in
the desired format. The following can be taken as the feature of a computer within itself that is the
expansion of the acronym “COMPUTER”
COMPUTER-Commonly Operated Machine Particularly Used for Technology, Education and Research
System Components: Before knowing the hardware concepts of a computer system in depth, it is
necessasary to know the main components of a computer system.
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Mother Board
Processors
Memory (RAM)
Case /Chassis
Power Supply
Floppy Disk Drive
Hard Disk Drive
CD ROM, DVD-ROM drive
Keyboard
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Mouse
Video card
Monitor (display)
Sound Card
Network Interface Controller (NIC)
Modems (internal and external)
Speakers
Printer
Scanner
Features of computer systems: All PC-Compatible system can be broken down into two basic system
types or class, of hardware:
1. 8-bit (PC, PC/XT- class) systems --it consists of only Floppy disk drive, Hard disk drive facility
2. 16/32/64-bit (PC/AT- class) systems-- these systems must have a processor that is compatible with Intel
286 or higher processors (including the 386, 486, Pentium, Pentium Pro, Pentium II, and Pentium III
Processors), and they must have a 16-bit or greater system bus.
The term PC stands for Personal Computer, XT stands for eXtended Technology (PC-XT),
AT stands for an Advanced Technology (PC-AT).
Difference between PC/XT and AT systems
System attributes
(8-bit) PC,XT Type
Supported processors
all x86 or x88
Processor modes
real
Software supported
16-bit only
Bus slot width
8-bit
Slot type
ISA only
Hardware Interrupts
8 (6 usable)
DMA channels
4(3 usable)
Maximum RAM
1MB
Floppy controller speed
250 kbps
Standard boot drive
360KB or 720KB
Keyboard interface
Unidirectional
CMOS memory /clock
None standard
Serial port UART
8250B
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(16/32/64-bit) AT type
286 or higher
real/protected/virtual real
16 or 32-bit
16/32/63-bit
ISA, EISA, MCA, PC-card, VL-bus, PCI &AGP
16(11 usable)
8(7 usable)
16MB/4GB or more
250/300/500/1,000 kbps
1.2MB/1.44MB/2.88MB
Bi-directional
MC146818 Compatible
16450/16550A
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The mother board components (Motherboard Selection Criteria):
The system unit is a box like unit filled with a no of useful components, each performing a discrete
function. These components work together to accomplish the main function of the computer. Which accepts
and process input and deliver output. Components of the system unit are the power supply with exhaust fan,
the speaker, the motherboard, the disk drives and the adaptor cards.
 Motherboard: The motherboard is the core of the system, A large board containing a number of tiny
electronic circuits and other components are visible termed as Motherboard. All peripheral devices is
connected to the motherboard and it controls everything in the system. , it is also known as main board,
system board and planer
 Processor: The processor is the “engine” or “brain” of the computer. It’s also called the CPU (central
processing unit).
 Memory (RAM): The system memory is often called RAM (for random access memory). This is the
primary working memory that holds all the programs and data, the processor is using at a given time
 Bus types: A Pentium, Pentium pro and Pentium II motherboards should have three or four ISA bus slots
and 3 or 4 PCI local bus slots.
 BIOS: The motherboard should use an industry standard BIOS such as those from AMI, Phoenix,
microid research or Award.
 Form factor: the physical dimensions and size of the board, and dictates what type of case the board will
fit into.
 Built in Interfaces: ideally, a motherboard should contain as many built in standard controllers and
interfaces as possible. A motherboard should have a built in floppy controller that supports 2.88m Drives.
Built in primary and secondnary local bus connectors, serial and parallel ports and built in ps/2 type
mouse port should be included.
 Plug and play (PnP): The motherboard should fully support the Intel PnP specification. This will allow
automatic configuration of PCI adaptor as well as PnP ISA adaptor.
 Power supply: The power supply feeds electrical power to the internal components of PC.
 Motherboard chipset: all Pentium and Pentium MMX motherboards should use a high performance
chipset preferably one that allows parity checking such as the Intel Triton II.
 Case/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
 Hard drive: The hard disk is the primary high-capacity storage media for the system
 Optical drive: CD (compact disc), DVD (digital versatile disc), and BD (Blu-ray disc) drives are
relatively high-capacity, removable-media, optical drives; most newer systems include drives featuring
write/rewrite capability.
 Keyboard: The keyboard is the primary input device on a PC that is used by a human to communicate
and control a system
 Mouse: Many types of pointing devices are available today, the first and most popular device for this
purpose is the mouse
 Video card: The video card controls the information you see on the monitor and this card. It may be
integrated into the motherboard.
 Monitor: The monitor or display shows information and is controlled by the video card
 Sound card: A sound card enables the PC to generate complex sounds.
 Network/modem: Most PCs ship with a wired or wireless network interface and possibly a modem.
 Documentation: Good technical documentation is requirement information include all jumpers,
switches, connector pin outs for all connectors, cache RAMS chips, SIMMs and other technical
information.
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Mother Board Form Factors: the most important component in a PC system is the main board or
motherboard. Several common form factors are used for PC motherboards. The form factor refers to the
physical dimensions (size and shape) as well as certain connector, screw hole, and other positions that dictate
into which type of case the board will fit. The more commonly known PC motherboard form factors include
the following:
Obsolete Form Factors
■ PC and XT
■ Full-size AT
■ Baby AT
■ LPX (semi proprietary)
■ NLX
■ WTX
■ BTX, microBTX, picoBTX
Modern Form Factors
■ ATX and variants; microATX, FlexATX, DTX/Mini-DTX, and ITX/Mini-ITX
Obsolete Form Factors
The following sections examine industry-standard motherboard form factors no longer in use, but which can
be commonly found on older systems.
1. PC XT form factor:
The first original IBM PC motherboard was released in August 1981. IBM followed the PC with the
XT motherboard in March 1983, which had the same size and shape as the PC board but had eight slots
instead of five. Both the IBM PC and XT motherboards were 9 inch×13 inch, Baby-AT with modifications
in screw hole positions to fit an AT style case.
The XT motherboard design became popular, and many other PC motherboard manufacturers of the
day copied IBM’s XT design and produced similar boards.
2. Full-size AT: The full size AT motherboard form factor matches the original IBM AT motherboard
design. first debuted in August 1984, This allows for a very large board up to 12 inches wide by 13.8 inches
deep. The keyboard connector and slot connector must conform to specific placement requirement to fit the
holes in the case.
The important thing to note about the full-size AT systems is that you can always replace a full-size
AT motherboard with a Baby-AT (or XT-size) board.
3. Baby- AT form factor:
The Baby-AT form factor size is 8.57 inches wide by 13.05 inches deep, released in mid-1996. This
form factor is essentially the same form factor as the original IBM XT motherboard. The only difference is a
slight modification in one of the screw hole positions to fit into an AT-style case. These motherboards also
have specific placement of the keyboard and slot connectors to match the holes in the case.
4. LPX form factor:
The LPX and mini-LPX form factor boards were a semi proprietary design that Western Digital
originally developed in 1987 for some of its motherboards. This board up to 13 inches by 9.0 inches. The LP
in LPX stands for Low Profile, which is so named because these boards incorporate slots that are parallel to
the main board, enabling the expansion cards to install sideways. This allows for a slim or low-profile case
design and overall a smaller system than the Baby-AT.
An LPX board has a row of connectors for video (VGA-15 pin), parallel port(25-pin), two serial
ports(9-pin each), and mini-DIN PS/2 style mouse and keyboard connector.
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5. NLX form factor: the NLX is the latest development in the desktop motherboard technology similar in
appearance to LPX, but with improvements designed to allow full integration of the latest technologies.
NLX is a low-profile form factor designed to replace the LPX design used in previous low-profile
systems. Introduced in November 1996 by Intel, NLX was a popular form factor in the late 1990s for
Slimline corporate desktop systems from vendors such as Compaq, HP, and Toshiba.
The main characteristic of an NLX system is that the motherboard plugs into the riser, unlike LPX
where the riser plugs into the motherboard. Therefore, the motherboard can be removed from the system
without disturbing the riser or any of the expansion cards plugged into it. All devices that normally plug into
the motherboard—such as drive cables, the power supply, the front panel light, switch connectors, and so
on—plug into the riser instead
6. WTX form factor: The WTX was a board and system form factor developed for the mid-range workstation
market; however, most vendors making workstations and servers have used the ATX form factor. WTX went
beyond ATX and defined the size and shape of the board and the interface between the board and chassis, as
well as required chassis features.
WTX was released in September 1998 (1.0) and updated in February 1999 (1.1). Since then, however, WTX
has been officially discontinued, and there will be no further updates.
6. BTX form factor: Balanced Technology Extended (BTX) is a motherboard form factor specification that
Intel released in September 2003, with 1.0a and 1.0b updates released in February 2004 and July 2005,
respectively.
BTX was designed to address the ever-increasing component power and cooling requirements, as
well as enabling improved circuit routing and more flexible chassis designs.
Each board has the same basic screw hole and connector placement requirements. So, if you have a
case that fits a full-size BTX board, you can also mount a microBTX or picoBTX board in that same case.
BTX uses the same power connectors as in the latest power supply form factor specifications,
including a 24-pin main connector for the board and a 4-pin ATX12V connector for the CPU voltage
regulator module.
ATX and Other Modern Form Factors
The following sections cover the industry-standard form factors, including ATX, that are popular on modern
systems.
1. ATX from factor: the ATX form factor is recently evolution in motherboard form factor. ATX is a
combination of the bet features of the Baby AT and LPX motherboard design with many new enhancements
and feature thrown in. This board up to 9.6 inches by 12 inches.
ATX is the most popular motherboard form factor for new systems and will continue to be popular in
the future.
ATX improved on the Baby-AT and LPX motherboard designs in several major areas:
■ Built-in double high external I/O connector panel—The rear portion of the motherboard includes a
stacked I/O connector area that is 6 1/4 inches wide by 1 3/4 inches tall. This enables external I/O connectors
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to be located directly on the board and minimizes the need for cables running from internal connectors to the
back of the case as with Baby-AT designs.
■ Single main keyed internal power supply connector—The ATX specification includes a keyed and
main power connector that is easy to plug in and install. This connector also features pins for supplying 3.3V
to the motherboard, helping to minimize the use of builtin voltage regulators that are susceptible to failure.
■ Relocated CPU and memory—The CPU and memory modules are relocated so they can’t interfere with
bus expansion cards and can easily be accessed for upgrade without removing any of the installed bus
adapters
■ Relocated internal I/O connectors—The internal I/O connectors for the floppy and hard disk drives are
relocated to be near the drive bays and out from under the expansion board slot and drive bay areas.
■ Improved cooling—The CPU and main memory are designed and positioned to improve overall system
cooling compared to Baby-AT and older designs.
■ Lower cost to manufacture—The ATX specification eliminates the need for the rat’s nest of cables to
external I/O port connectors found on Baby-AT motherboards.
Mini-ATX form factor: it is simply referenced as a slightly smaller version of ATX. which is a fully
compatible subset of ATX that fits into the same case, The Mini-ATX board is 11.2 inches×8.2 inches
(284mm×208mm).
MicroATX form factor:
The microATX motherboard maximum size is only 9.6 inches×9.6 inches as compared to the fullsize ATX size of 12 inches×9.6 inches.
MicroATX is a motherboard form factor Intel introduced in December 1997 as an evolution of the
ATX form factor for smaller and lower-cost systems. The reduced size compared to standard ATX allows for
a smaller chassis, motherboard, and power supply, thereby reducing the cost of the entire system. The
microATX form factor is also backward-compatible with the ATX form factor and can be used in full-size
ATX cases.
The sound and video are usually integrated on the motherboard and therefore don’t require separate
slots. This higher integration reduces motherboard and system costs.
The microATX form factor is similar to ATX for compatibility. The similarities include the following:
■ Standard ATX power connectors
■ Standard ATX I/O panel
■ Mounting holes and dimensions are a subset of ATX
FlexATX form factor:
In March 1999 Intel released the FlexATX. FlexATX defines a board that is up to 9 inches×7.5
inches, which is the smallest of the ATX family boards. In all other ways, FlexATX is the same as ATX and
microATX, making FlexATX fully backward compatible with ATX or microATX by using a subset of the
mounting holes and the same I/O and power supply connector specifications.
DTX and Mini-DTX form factor:
The DTX (and Mini-DTX) specification was released in February 2007 by AMD as smaller
variations of the microATX and FlexATX specifications, respectively. DTX boards are up to 8 inches×9.6
inches, whereas Mini-DTX boards are a shorter version at only 8 inches×6.7 inches.
The narrow 8-inch width for both DTX and Mini-DTX boards allows for only two expansion slots.
Motherboards produced in these form factors can be installed in microATX, FlexATX cases, or Mini-ITX
cases.
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ITX and Mini-ITX form factor:
In April 2002, VIA created an even smaller board that featured the absolute minimum width and
depth dimensions allowed by FlexATX. The company called it Mini-ITX. A Mini-ITX board fits in any
chassis that accepts a FlexATX board.
The Mini-ITX form factor was designed by VIA especially to support VIA’s low-power embedded
Eden ESP and C3 E-Series processors.
The table shows various mother board form factors are as follows:
Form
Width
Length
Design Type
Case Type
IBM PC
8.5
13
Motherboard
IBM PC
IBM PC-XT
8.5
13
Motherboard
IBM PC-XT
Baby AT
8.57
13.05
Motherboard
Baby AT Desktop or
Tower
Full-size AT
12
13.8
Motherboard
AT Desktop or Tower
LPX
9
11-13
Backplane
Low Profile
NLX
8-9
10-13.6
Backplane
Low Profile
WTX
12
9.6
Motherboard
ATX Desktop or
Tower
12.8
10.5
BTX
Motherboard
Desktop or Tower
ATX
12
9.6
Motherboard
ATX Desktop or
Tower
Mini-ATX
11.2
8.2
Motherboard
Smaller ATX Desktop
Micro-ATX
9.6
9.6
Motherboard
Low Profile
Flex-ATX
9
7.5
Motherboard
Flexible design
DTX
8
9.6
Motherboard
Low Profile
Mini DTX
8
6.7
Motherboard
FLEX ATX
ITX
8.5
7.5
Motherboard
FLEX ATX
Mini ITX
6.7
6.7
Motherboard
FLEX ATX
Year
March 1983
March 1983
mid-1996,
August 1984,
in 1987
November 1996
September 199
September 2003
July 1995.
December 1997
In March 1999,
February 2007
April 2002
Motherboard interface connectors and connections:
There are a variety of different connectors on a modern motherboards. The pin values of some of the connectors
are as follows
PIN
SIGNAL NAME
PIN
1
2
3
+3.3 V
+3.3 V
Ground
11
12
13
4
5
6
7
8
9
10
+5 V
Ground
+5 V
Ground
PWGRD(Power Good)
+5 VSB(Standby)
+12 V
14
15
16
17
18
19
20
SIGNAL NAME
+3.3 V
-12 V
Ground
PS-ON(Power Supply Remote On-Off Control)
Ground
Ground
Ground
-5 V
+5 V
+5 V
Table 1: ATX Motherboard Power Connectors (20-pins)
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PIN
1
2
3
4
5
6
SIGNAL NAME
PWGRD(Power Good)
+5 V
+12 V
-12 V
Ground
Ground
PIN
7
8
9
10
11
12
SIGNAL NAME
Ground
Ground
-5 V
+5 V
+5 V
+5 V
Table 2: Baby - AT Motherboard Power Connectors (12-pins)
PIN
1
2
3
4
5
SIGNAL NAME
DCD(Data Carrier Detect)
DSR(Data Set Ready)
SIN(Serial - In)
RTS(Request to Send)
SOUT(Serial -Out)
PIN
6
7
8
9
10
SIGNAL NAME
CTS(Clear to Send
DTR(Data Terminal Ready)
RI(Ring Indicator)
GND(Ground)
N/C(Not Connected)
Table 3: Serial Port Pin-Header Connectors (10-pins)
PIN
1
2
3
4
SIGNAL NAME
PIN
GND
Data
N/C
Vcc
5
6
7
8
SIGNAL NAME
CLK(Clock)
KEY
KEY
N/C
Table 4: Motherboard Mouse Pin-Header Connectors
Signal name
Pin
Pin
Signal name
STROBE
1
2
AUTO FEED
Data Bit 0
3
4
ERROR
Data Bit 1
5
6
Init
Data Bit 2
7
8
SLCT IN
Data Bit 3
9
10
Ground
Data Bit 4
11
12
Ground
Data Bit 5
13
14
Ground
Data Bit 6
15
16
Ground
Data Bit 7
17
18
Ground
ACJ
19
20
Ground
BUSY
21
22
Ground
PE(Paper End)
23
24
Ground
SLCT
25
26
Not Connector
Table 5 : parallel port Pin Header connector
Pin
1
2
BCA II/I
Signal name
Ground
Unused
Table 6 : Battery Connector
I.T HARDWARE
Pin
3
4
Signal name
Key
+4 to 6v
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Pin
1
2
Signal name
Ground
Key
Table 7 : Speaker Connector
Pin
3
4
Signal name
Board mounted speaker
Speaker output
Pin
Signal name
1
Ground
2
+12 v
3
Sense tachometer
Table 8 : Microprocessor fan power Connector
The USB Pinout:
Pin Name
Cable color
BCA II/I
Description
1
VCC
Red
+5 VDC
2
D-
White
Data -
3
D+
Green
Data +
4
GND
Black
Ground
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