PC Fundamentals
Presentation 17 – Buses
Copyright © 2007 Heathkit Company, Inc. All Rights Reserved
Objectives
At the end of this presentation,
you will be able to:
2

Define computer bus and explain its
purpose.
 Define the following terms: ISA, MCA,
EISA, VL-Bus, PCI, PCI Express, and AGP.
 Discuss the characteristics of the PCI, PCI
Express, and AGP buses.
 Recognize the connector (or slot) of an ISA,
PCI, PCI Express, and VGA bus.
3
CPU
Parallel Port
Memory
Keyboard Controller
Video
Adapter
The Data Bus
System Controller
4
CPU
Memory
Keyboard Controller
Video
Adapter
System Controller
5
CPU
Memory
Video
Adapter
6
7
What is a Bus?

Signal Pathways

A way of passing information between
components inside and outside the
computer.

A modular way of expanding the functions
or capabilities of the computer.
8
PC Bus Architectures

ISA
 MCA
 EISA
 VL-Bus
 PCI
 AGP
 PCI Express
9
The Original IBM PC Bus

Introduced on the original IBM PC

8-bit data path

4.77-MHz clock

8 Interrupts – Only one of which was
available for expansion boards.

4 DMA Channels – Only one of which was
available for expansion boards.
10
The Original IBM PC Bus
8-Bit Card
8-Bit Slot
11
Industry Standard Architecture
(ISA) Bus
 Introduced
on the IBM AT Computer
 16-bit data path
 Backward compatible with IBM-PC Bus
 8-MHz clock
 15 Interrupts
 7 DMA Channels
12
Industry Standard Architecture
(ISA) Bus
16-Bit Card
16-Bit Slot
8-Bit Section
Added Pins
13
Industry Standard Architecture
(ISA) Bus
8-Bit Card
16-Bit Slot
14
Micro-Channel Architecture (MCA)
Bus

Introduced on the IBM PS/2
 16-bit or 32-bit data path
 10-MHz clock
 Configured by software rather than by
jumpers or switches
 Not compatible with the ISA bus
 Bus Mastering
15
Bus Mastering
 Allows
data to be passed from one
device to another without CPU
intervention.
 Allows
a controller card to take control
of the bus, leaving the CPU free to
concentrate on other tasks.
16
Bus Mastering vs. DMA

DMA can send data from peripheral to
RAM or from RAM to peripheral, without
the intervention of the CPU.

Bus Mastering can send data from
peripheral to peripheral, without the
intervention of the CPU.
17
Extended ISA Bus (EISA)

The industry’s answer to the MCA bus

Backward compatible with ISA

16-bit or 32-bit data path

8-MHz Clock

Configured by software, not jumpers or
switches

Bus Mastering
18
CPU
High Speed
CPU Bus
BUS
Controller
Low Speed
I/O Bus
ISA Bus
Slots
19
CPU
Local Bus
Slots
High Speed
CPU Bus
BUS
Controller
Low Speed
I/O Bus
ISA Bus
Slots
20
VESA Local Bus (VL-Bus)
 Clock
speed same as the processor
 32-bit
data path
 Regular
ISA slot with local bus
connector added
 Bus
Mastering
21
Peripheral Component Interconnect
(PCI)
 Developed
for Pentium-class
processors
 32-bit
and 64-bit data path versions
 33-MHz
Clock
 Processor
 Plug
Independent
and Play with Bus Mastering
22
Peripheral Component Interconnect
(PCI) Bus
23
PCI Evolution

32-bit, 33 MHz
 64-bit, 33 MHz
 32-bit, 66 MHz
 64-bit, 66 MHz
24
PCI-X

PCI-X 66
 PCI-X 133
 PCI-X 266
 PCI-X 533
64-bit
64-bit
64-bit
64-bit
66 MHz
133 MHz
266 MHz
533 MHz
25
PCI Express
 The
next generation of PCI.
 Serial data paths.
 Very high speed (2500 MHz)
 Scales easily as additional serial data
paths are added.
 X1 has one serial path, X4 four serial
paths, etc.
26
PCI-Express @ 2500 MHz

PCI Express x1
 PCI Express x4
 PCI Express x8
 PCI Express x16
 PCI Express x32
Lanes
Bandwidth
1
4
8
16
32
250 Mbps
1000 Mbps
2000 Mbps
4000 Mbps
8000 Mbps
27
PCI and PCI Express Slots
PCI Express X 16
PCI Express X 1
Conventional PCI
Conventional PCI
28
Accelerated Graphics Port (AGP)

Developed for high speed graphics cards

Frees the PCI bus from making video
transfers

Used only for video cards

Considered a port rather than a bus

66 MHz, 32-Bit
29
Accelerated Graphics Port
(AGP)
30
AGP Modes
32-bits @ 66 MHz
Data Cycles
Per Clock

AGP
 AGP 2X
 AGP 4X
 AGP 8X
1
2
4
8
Bandwidth
266 Mbps
533 Mbps
1066 Mbps
2133 Mbps
31
PC Fundamentals
End
Copyright © 2007 Heathkit Company, Inc. All Rights Reserved