Computer maintenance & IT support service

Introduction
Bus
 Types of Bus
 Expansion Buses
Cards
 The Video Card
 The Sound Card
 Network card
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Computer systems generally consist of three main parts:
the central processing unit (CPU) that processes data,
memory that holds the programs and data to be processed,
and I/O (input/output) devices as peripherals that
communicate with the outside world.
 An early computer might contain a hand-wired CPU of
vacuum tubes, a magnetic drum for main memory, and a
punch tape and printer for reading and writing data
respectively.
 A modern system might have a multi-core CPU, DDR4
SDRAM for memory, a solid-state drive for secondary
storage, a graphics card and LCD as a display system, a
mouse and keyboard for interaction, and a Wi-Fi connection
for networking.
In both case, computer of one form or another move
data between all of these devices.
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A bus is a pathway on the motherboard that enables
the components to communicate with the CPU. The
common buses include ISA, EISA, VESA local bus,
PCI, AGP, and USB.
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Computers have two major types of buses:
1. System bus:- This is the bus that connects the CPU
to main memory on the motherboard.
The system bus is also called the front-side bus,
memory bus, local bus, or host bus.
2. A number of I/O Buses, (I/O is an acronym for input
/ output), connecting various peripheral devices to the
CPU. These devices connect to the system bus via a
‘bridge’ implemented in the processors chipset. Other
names for the I/O bus include “expansion bus",
"external bus” or “host bus”.
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In most traditional computer architectures, the
CPU and main memory tend to be tightly coupled.
A microprocessor conventionally is a single chip
which has a number of electrical connections on
its pins that can be used to select an "address" in
the main memory and another set of pins to read
and write the data stored at that location.
In most cases, the CPU and memory share
signaling characteristics and operate in synchrony.
The bus connecting the CPU and memory is one of
the defining characteristics of the system, and
often referred to simply as the system bus.
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The system bus is a little bit more complicated than a single train
track, but not too much. Think of it as three rails per track, kind
of like mass transit trains use. That's because each track has to
carry three different things: data, address, and control.
 The data are the actual digital pieces of information that need
to get somewhere or do something.
 The address information describes where the data is located
and where it needs to go during a particular operation.
 The control part is like the instructions because data doesn't
know what to do with itself (think 'Lego Movie'), so this
manages the flow of address and data information. That
includes which direction for the transfer of information and
exactly how data needs to be routed through the computer
system.
Because of these three different types of information, the system
bus actually consists of three buses.
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It is possible to allow peripherals to communicate with memory in
the same fashion, attaching adaptors in the form of expansion
cards directly to the system bus. This is commonly accomplished
through some sort of standardized electrical connector, several of
these forming the expansion bus or local bus.
Expansion Bus Types:- These are some of the common expansion
bus types that have ever been used in computers:
 ISA - Industry Standard Architecture
 EISA - Extended Industry Standard Architecture
 MCA - Micro Channel Architecture
 VESA - Video Electronics Standards Association
 PCI - Peripheral Component Interconnect
 PCMCIA - Personal Computer Memory Card Industry Association
(Also called PC bus)
 AGP - Accelerated Graphics Port
 SCSI - Small Computer Systems Interface.Aschalew S.(Msc) 9

However, as the performance differences between
the CPU and peripherals varies widely, some
solution is generally needed to ensure that
peripherals do not slow overall system
performance.
 Many CPUs feature a second set of pins similar
to those for communicating with memory, but able
to operate at very different speeds and using
different protocols. Others use smart controllers to
place the data directly in memory, a concept
known as direct memory access. Most modern
systems combine both solutions, where
appropriate.
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As the number of potential peripherals grew, using an
expansion card for every peripheral became increasingly
untenable. This has led to the introduction of bus systems
designed specifically to support multiple peripherals.
Common examples are the SATA ports in modern
computers, which allow a number of hard drives to be
connected without the need for a card. However, these
high-performance systems are generally too expensive to
implement in low-end devices, like a mouse. This has led
to the parallel development of a number of low-
performance bus systems for these solutions, the most
common example being the standardized Universal Serial
Bus (USB). All such examples may be referred to as
peripheral buses, although this terminology is not
universal.
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The internal bus, also known as internal data bus,
memory bus, system bus or Front-Side-Bus, connects
all the internal components of a computer, such as
CPU and memory, to the motherboard. Internal data
buses are also referred to as a local bus, because they
are intended to connect to local devices. This bus is
typically rather quick and is independent of the rest of
the computer operations.
The external bus, or expansion bus, is made up of the
electronic pathways that connect the different external
devices, such as printer etc., to the computer.
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parallel buses, which carry data words in parallel
on multiple wires, but serial buses, which carry
data in bit-serial form.
The addition of extra power and control
connections, differential drivers, and data
connections in each direction usually means that
most serial buses have more conductors than the
minimum of one used in 1-Wire and UNI/O.
As data rates increase, the problems of timing
slope, power consumption, electromagnetic
interference and crosstalk across parallel buses
become more and more difficult to avoid.
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One partial solution to this problem has been to
double pump the bus.
 Often, a serial bus can be operated at higher
overall data rates than a parallel bus, despite
having fewer electrical connections, because a
serial bus inherently has no timing angle or
crosstalk. USB, FireWire, and Serial ATA are
examples of this.
Multi drop connections do not work well for fast
serial buses, so most modern serial buses use daisy-
chain or hub designs.
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An address bus is a computer bus (a series of lines
connecting two or more devices) that is used to specify
a physical address.
 When a processor or DMA-enabled device needs to
read or write to a memory location, it specifies that
memory location on the address bus (the value to be
read or written is sent on the data bus).
The width of the address bus determines the amount
of memory a system can address. For example, a
system with a 32-bit address bus can address 232
(4,294,967,296) memory locations. If each memory
location holds one byte, the addressable memory space
is 4 GB.
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Non-existent address
Software instructs the CPU to read or write a specific
physical memory address.
Accordingly, the CPU sets this physical address on its
address bus and requests all other hardware connected to
the CPU to respond with the results, if they answer for this
specific address.
 If no other hardware responds, the CPU raises an
exception, stating that the requested physical address is
unrecognized by the whole computer system. Note that this
only covers physical memory addresses.
Trying to access an undefined virtual memory address is
generally considered to be a segmentation fault rather than
a bus error, though if the MMU is separate, the processor
can't tell the difference.
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Unaligned access
Most CPUs are byte-addressable, where each unique
memory address refers to an 8-bit byte.
Most CPUs can access individual bytes from each
memory address, but they generally cannot access
larger units (16 bits, 32 bits, 64 bits and so on) without
these units being "aligned" to a specific boundary (the
x86 platform being a notable exception).
For example, if multi-byte accesses must be 16 bit-
aligned, addresses (given in bytes) at 0, 2, 4, 6, and so
on would be considered aligned and therefore accessible,
while addresses 1, 3, 5, and so on would be considered
unaligned.
Similarly, if multi-byte accesses must be 32-bit aligned,
addresses 0, 4, 8, 12, and so on would be considered
aligned and therefore accessible, and all addresses in
between would be considered unaligned.Aschalew S.(Msc) 17

Some systems may have a hybrid of these depending on the
architecture being used. For example, for hardware based
on the IBM System/360 mainframe, including the IBM
System z, Fujitsu B8000, RCA Spectra, and UNIVAC Series
90, instructions must be on a 16-bit boundary, that is,
execution addresses must start on an even byte.
Attempts to branch to an odd address results in a
specification exception. Data, however, may be retrieved
from any address in memory, and may be one byte or longer
depending on the instruction.
CPUs generally access data at the full width of their data
bus at all times. T
o address bytes, they access memory at the full width of
their data bus, then mask and shift to address the
individual byte.
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Paging errors
FreeBSD, Linux and Solaris can signal a bus
error when virtual memory pages cannot be
paged in, e.g. because it has disappeared (e.g.
accessing a memory-mapped file or executing
a binary image which has been truncated
while the program was running), or because a
just-created memory-mapped file cannot be
physically allocated, because the disk is full.
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Non-present segment (x86)
On x86 exists an older memory management
mechanism known as segmentation.
If the application loads segment register with the
selector of non-present segment (which under
POSIX-compliant OSs can only be done with an
assembly language), the exception is generated.
 Some OS used that for swapping, but under
Linux this generates SIGBUS.
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Summary of functions of buses in computers
Data sharing - All types of buses found in a computer
transfer data between the computer peripherals
connected to it.
The buses transfer or send data in either serial or
parallel method of data transfer.
This allows for the exchange of 1, 2, 4 or even 8 bytes
of data at a time. (A byte is a group of 8 bits).
Buses are classified depending on how many bits
they can move at the same time, which means that
we have 8-bit, 16-bit, 32-bit or even 64-bit buses.
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Addressing - A bus has address lines, which match
those of the processor.
This allows data to be sent to or from specific
memory locations.
Power - A bus supplies power to various peripherals
connected to it.
Timing - The bus provides a system clock signal to
synchronize the peripherals attached to it with the
rest of the system.
The expansion bus facilitates easy connection of
more or additional components and devices on a
computer such as a TV card or sound card.
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IBM introduced what became the Industry Standard
Architecture (ISA) I/O bus with its first mainstream
PC, the 8088.
The ISA bus ran at a clock speed of 4.77 MHz.
The initial ISA bus was 8-bits wide and offered IRQs 0-
7. The 16-bit ISA bus came out in 1984. This newer
ISA bus runs at 8.3 MHz and supports IRQs (interrupt
requests) 0-15. Although both ISA cards are different
sizes, both can be used in a 16-bit ISA slot. A moth-
erboard with both 8-bit and 16-bit ISA slots.
You can still see ISA slots in many computers today
that support both 8- and 16-bit cards.
Exam Tip:- The 16-bit ISA slots support the use of
either 8-bit or 16-bit ISA cards.
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For the 80286-based IBM PC-AT, an improved bus design,
which could transfer 16-bits of data at a time, was
announced. The 16-bit version of the ISA bus is sometimes
known as the AT bus. (AT-Advanced Technology)
The improved AT bus also provided a total of 24 address
lines, which allowed 16MB of memory to be addressed. The
AT bus was backward compatible with its 8-bit predecessor
and allowed 8-bit cards be used in 16-bit expansion slots.
When it first appeared the 8-bit ISA bus ran at a speed of
4.77MHZ – the same speed as the processor.
 Improvements done over the years eventually made the AT
bus ran at a clock speed of 8MHz.
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(
)
Compaq formed the committee that created the Extended Industry Standard
Architecture (EISA) as an open standard for bus architecture to compete with
IBM's proprietary micro channel architecture (MCA).
The EISA bus is 32-bits wide, has an 8.3-MHz bus speed, and supports bus
mastering. EISA slots look similar to ISA slots and in fact support ISA cards
as well as EISA cards.
 Back in EISA's heyday, techs loved working with pure EISA systems, because
EISA could automatically configure expansion cards when you ran the
configuration program. No manual configuration of IRQs or I/O addresses
made EISA a clever bus for its time.
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This is a bus technology developed by a group of
manufactures as an alternative to MCA. The bus
architecture was designed to use a 32-bit data path and
provided 32 address lines giving access to 4GB of memory.
Like the MCA, EISA offered a disk-based setup for the
cards, but it still ran at 8MHz in order for it to be
compatible with ISA.
The EISA expansion slots are twice as deep as an ISA
slot. If an ISA card is placed in an EISA slot it will use
only the top row of connectors, however, a full EISA card
uses both rows. It offered bus mastering.
EISA cards were relatively expensive and were normally
found on high-end workstations and network servers.
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The Video Electronics Standards Association created
the VESA local bus (VL-bus) technology in 1992 as an
enhancement of the ISA bus.
The 32-bit-wide VL-bus works with hard drive
controllers and increases video performance.
The introduction of Windows created the need for more
advanced graphics, and running at incredible speeds of
33 MHz, the VL-bus is up to the challenge.
VL-bus slots are similar in size to 16-bit ISA slots and
have an extra brown slot at the end.
ISA cards are compatible with the VL-bus technology
and can be placed in the ISA portion of VL-bus slots
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It was also known as the Local bus or the VESA-Local bus.
VESA (Video Electronics Standards Association) was
invented to help standardize PCs video specifications, thus
solving the problem of proprietary technology where
different manufacturers were attempting to develop their
own buses.
The VL Bus provided 32-bit data path and ran at 25 or 33
MHZ.
It ran at the same clock frequency as the host CPU.
But this became a problem as processor speeds increased
because, the faster the peripherals are required to run, the
more expensive they are to manufacture.
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It was difficult to implement the VL-Bus on newer chips such as
the 486s and the new Pentiums and so eventually the VL-Bus
was superseded by PCI.
VESA slots had extra set of connectors and thus the cards were
larger. The VESA design was backward compatible with the
older ISA cards.
Features of the VESA local bus card:-
32-bit interface
62/36-pin connector
90+20 pin VESA local bus extension
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Peripheral Component Interconnect (PCI) was introduced
in 1993 and quickly made its way into the hearts of techs.
The 32-bit-wide PCI bus runs at half the speed of the
processor (up to 33 MHz), which at the time of its
creation made this bus an excellent choice for graphics
and video.
 Manufacturers began creating peripherals that could
take advantage of these increased speeds. Better still, the
PCI bus automatically configures PCI cards, which
means the end of messing with manual configuration of
IRQs and other resources.
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It is one of the latest developments in bus architecture and
is the current standard for PC expansion cards.
It is a local bus like VESA, that is, it connects the CPU,
memory and peripherals to wider, faster data pathway.
PCI supports both 32-bit and 64-bit data width; it is
compatible with 486s and Pentiums. The bus data width is
equal to the processor, such as, a 32 bit processor would
have a 32 bit PCI bus, and operates at 33MHz.
PCI was used in developing Plug and Play (PnP) and all
PCI cards support PnP. This means a user can plug a new
card into the computer, power it on and it will “self-
identify” and “self-specify” and start working without
manual configuration using jumpers.
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Unlike VESA, PCI supports bus mastering that is, the
bus has some processing capability and thus the CPU
spends less time processing data.
Most PCI cards are designed for 5v, but there are also 3v
and dual-voltage cards.
 Keying slots used help to differentiate 3v and 5v cards
and also to make sure that a 3v card is not slotted into a
5v socket and vice versa.
Nowadays, 3-D graphics and video require even more
than the 32-bit PCI bus can offer; manufacturers
introduced 64-bit PCI bus to handle the load. Today, pri-
marily only modern server network interface cards
(NICs) use the 64-bit PCI bus, because for mainstream
video, the bus has been eclipsed by a new bus technology
called AGP
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Accelerated Graphics Port (AGP) was designed specifically for
video. The need for high quality and very fast performance of
video on computers led to development of the Accelerated
Graphics Port (AGP).
A subset of PCI and thus completely plug and play, AGP
provides a direct connection between processor and the video
card.
 AGP connects directly to the North Bridge of the Intel 800
series chipset. The bus comes in 32-bit- and 64-bit-wide bus
widths.
The 32-bit-wide AGP bus operates at the speed of the
processor's memory bus (up to 66 MHz) making it perfect for
3-D graphics.
The 64-bit AGP 4x bus operates at the speed of the system bus
up to 133 MHz AGP 4x can move data at a rate of 1.07 GB per
second using the maximum transfer rate formula.
AGP slots are brown and similar in size to PCI slots. But AGP
and PCI cards cannot use the same slots.
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The AGP Port connects to the CPU and operates at the speed of
the processor bus. This means that video information is sent more
quickly to the card for processing.
The AGP uses the main PC memory to hold 3D images. In effect,
this gives the AGP video card an unlimited amount of video
memory. To speed up the data transfer, Intel designed the port as
a direct path to the PC’s main memory.
Data transfer rate ranges from 264 Mbps to 528mbps, 800 Mbps
up to 1.5 GB/sec. AGP connector is identified by its brown color.
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Short for Small Computer System Interface, a
parallel interface standard used by Apple
Macintosh computers, PC's and Unix systems
for attaching peripheral devices to a computer.
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USB differs from the buses discussed so far; it is an
external bus that works with the PCI internal bus. Most
ATX motherboards have built-in USB ports, or you can
install a PCI card that offers the ports.
USB (specification 1.0) transfers data at rates of 12 Mbps
and enables you to daisy chain up to 127 USB devices
together. The newer USB 2.0 specification is even faster.
USB is hot-swappable and supports the Plug and Play
technology. You can add and remove USB devices on the
fly without opening the case-you simply plug them in and
you can use them right away.
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It is external bus standard that supports data transfer rates of
12 Mbps. A single USB port connects up to 127 peripheral
devices, such as mice, modems, and keyboards. The USB also
supports hot plugging or insertion (ability to connect a device
without turning the PC of) and plug and play (You connect a
device and start using it without configuration).
We have two versions of USB:-
 USB 1x:- followed with two data rates: 12 Mbps for
devices such as disk drives that need high-speed
throughput and 1.5 Mbps for devices such as joysticks
that need much less bandwidth.
 USB 2x:-It increased the data transfer rate for PC to
USB device to 480 Mbps, which is 40 times faster than
the USB 1.1 specification. With the increased
bandwidth, high throughput peripherals such as digital
cameras, CD burners and video equipment could now
be connected with USB.
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Modems connect to your telephone line using RJ-11
connectors. RJ-11 connectors use two wires and are
identical to telephone connectors.
The locking clips on the RJ-11 connectors help
secure the cable into the jack, or port. RJ-11 ports
look identical to phone jacks and are found on your
modem.
All modems have at least one RJ-11 port, and many
modems have two RJ-11 ports -one for the modem
and the other for a telephone, so you can use the
telephone line for voice when the modem is not in
use.
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Plugs into expansion slot
Provides physical interface between computer and
network medium
Most computers use parallel data lines, called a bus, to
send data between CPU and adapter cards
Most networking media transmits data in single line,
called serial transmission
NIC translates parallel into serial for outgoing
messages and serial into parallel for incoming messages
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For any computer, a network interface card (NIC)
performs two crucial tasks
Establishes and manages the computer’s network
connection
Translates digital computer data into signals
(appropriate for the networking medium) for outgoing
messages, and translates signals into digital
computer data for incoming messages
NIC establishes a link between a computer and a
network, and then manages that link
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Installing a Network Interface Card (NIC) into any
version of Windows is usually a easy, as most NICs today
are completely plug and play. For the most part, this is
simply a matter of turning off the PC, installing the card,
and turning the system back on.
The only trick is remembering to use the disk that comes
with the NIC, even if Windows offers to use its own
drivers. All the issues discussed with respect to installing
devices also hold true for NICs-just because they're
network cards doesn't mean anything else special needs to
happen,
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The Video Card
The Sound Card
TV card
Network card
Aschalew S.(Msc) 43
Types of computer
adapter card

Aschalew S.(Msc) 44
Table-1Expansion Slot and Card Compatibility(shows you which
expansion cards go with which I/O busses.)
8-bit
ISA
16-bit
ISA
EISA VL-bus PCI AGP USB
8-bit ISA cards yes yes yes yes no no no
16-bit ISA cards no yes yes yes no no no
EISA cards yes yes yes no no no no
VL-bus cards no no no yes no no no
PCI cards no no no no yes no no
AGP cards no no no no no yes no
USB devices no no no no no no yes

1. What is the main difference and similarities
among available adapter card?
2. Why need to install computer adapter card on a
motherboard?
3. Is there any interrelation among adapter card,
expansion slot and buses? If yes describe it.
Aschalew S.(Msc) 45

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