Bus & Interface

1. Bus Architecture & Interface
Imranul Hasan
Greenwich University, UK

2. Bus
 A collection of wires and electronic
components through which data is
transmitted from one part of a computer to
another, even from one computer to another
computer. When used in reference to
personal computers, the term bus usually
refers to internal bus.
 All buses consist of three parts -- an address
bus, control bus and a data bus.

4. North/South Bridgearchitectures

7. Internal Bus/ Internal Data Bus
 Internal Bus/ Internal Data Bus: A bus that operates only
within the internal circuitry of the CPU, communicating among
the internal caches of memory that are part of the CPU chip’s
design.
 Microprocessors communicate with its internal and external
components through the bus, are mainly divided into two
categories:
1. Front-side Bus: Another name for the system bus. The bus
that connects the CPU to main memory on the motherboard.
The system bus is also called the memory bus, local bus, or
host bus.
2. Backside bus: A microprocessor bus that connects the CPU to
a Level 2 cache. Typically, a backside bus runs at a faster clock
speed than the frontside bus that connects the CPU to main
memory.

8. Expansion Bus
 A collection of wires and protocols that allows the expansion of a
computer by inserting printed circuit boards (expansion boards).
 AT Bus: The AT bus, which runs at 8 megahertz and has a 16-
bit data path. The AT bus is sometimes referred to as the ISA
bus.
 ISA Bus: Short for Industry Standard Architecture bus. 16 bit
bus. ISA began to be replaced by the PCI local bus architecture.
 MCA: IBM introduced the Micro Channel Architecture (MCA) in
1987. 32-bit bus.
 EISA Bus: A more successful alternative to the MCA bus is the
Extended Industry Standard Architecture (EISA ), a high-speed
32-bit bus architecture developed by a group of IBM's
competitors.

9. Expansion Bus
 VL-bus: Short for VESA Local-Bus, a local bus architecture
created by the Video Electronics Standards Association
(VESA ). Although it was quite popular in PCs made in 1993
and 1994, it has been overshadowed by a competing local
bus architecture called PCI.
 PCI Bus: Short for Peripheral Component Interconnect, a
local bus standard developed by Intel Corporation. PCI is a
64-bit bus, though it is usually implemented as a 32-bit bus. It
can run at clock speeds of 33 or 66 MHz. At 32 bits and 33
MHz, it yields a throughput rate of 133 MBps.
 PCI-X Bus: Short for PCI extended, an enhanced PCI bus.
PCI-X is backward-compatible with existing PCI cards. It
improves upon the speed of PCI from 133 MBps to as much
as 1 GBps.

10. Expansion Bus
 PCI Express: An I/O interconnect bus standard that
doubles the data transfer rates of original PCI. PCI
Express was designed to replace the general-purpose
PCI expansion bus, the high-end PCI-X bus and the AGP
graphics card interface.
 Data transfer rates of approximately 200MB/s.
 PCI Express, also known as 3GIO (for third-generation
Input/Output) is compatible with existing PCI systems.
 NuBus: The expansion bus for versions of the Macintosh
computers starting with the Macintosh II and ending with
the Performa. Current Macs use the PCI bus.
 SMBus: The System Management Bus (SMBus) is a
two-wire interface through which simple power-related
chips can communicate with rest of the system. With the
SMBus, a device can provide manufacturer information,
tell the system what its model or part number is, save its
state for a suspend event, report different types of errors,
accept control parameters and return its status.

11. PCI Express
 An I/O interconnect bus standard (which includes a protocol and a layered
architecture) that expands on and doubles the data transfer rates of original
PCI.
 Each lane of a PCI Express connection contains two pairs of wires -- one to
send and one to receive. Packets of data move across the lane at a rate of one
bit per cycle. A x1 connection, the smallest PCIe connection, has one lane
made up of four wires. It carries one bit per cycle in each direction. A x2 link
contains eight wires and transmits two bits at once, a x4 link transmits four
bits, and so on. Other configurations are x12, x16 and x32.
 The "x" in an "x16" connection stands for "by." PCIe connections are
scalable by one, by two, by four, and so on.
 PCI Express is available for desktop and laptop PCs. Its use may lead to
lower cost of motherboard production, since its connections contain fewer
pins than PCI connections do. It also has the potential to support many
devices, including Ethernet cards, USB 2 and video cards.
 PCI Express is a two-way, serial connection that carries data in packets
along two pairs of point-to-point data lanes, compared to the single parallel
data bus of traditional PCI that routes data at a set rate.
 Initial bit rates for PCI Express reach 2.5Gb/s per lane direction, which equate
to data transfer rates of approximately 200MB/s.
 PCI Express, also known as 3GIO (for third-generation Input/Output) is
compatible with existing PCI systems.

12. Expansion Bus
 PCI Express:
Each lane of a PCI Express
connection contains two pairs of
wires -- one to send and one to
receive. Packets of data move
across the lane at a rate of one bit
per cycle. A x1 connection, the
smallest PCIe connection, has one
lane made up of four wires. It
carries one bit per cycle in each
direction. A x2 link contains eight
wires and transmits two bits at
once, a x4 link transmits four bits,
and so on. Other configurations
are x12, x16 and x32.

13. Expansion Bus
 PCI Express:

14. Expansion Bus
 Make Sure you have a PCI-E PCI Express
Slot on your MotherBoard

15. External Bus
 Another name for external data bus. A bus that connects a
computer to peripheral devices. Two examples are the
Universal Serial Bus (USB) and IEEE 1394.
 USB 1.1: Short for Universal Serial Bus, an external bus
standard that supports data transfer rates of 1.5 MBps. A single
USB port can be used to connect up to 127 peripheral devices.
 USB 2.0: Also referred to as Hi-Speed USB, USB 2.0 is an
external bus that supports data rates up to 60MBps.
 USB OTG: Short for USB On-The-Go, an extension of the USB
2.0 specification for connecting peripheral devices to each other.
USB OTG products can communicate with each other without the
need to be connected to a PC.
 IEEE 1394: A very fast external bus standard that supports data
transfer rates of up to 50MBps (in 1394a) and 100MBps (in
1394b). Products supporting the 1394 standard go under
different names, depending on the company. Apple, which
originally developed the technology, uses the trademarked name
FireWire. Other companies use other names, such as i.link and
Lynx, to describe their 1394 products.
 A single 1394 port can be used to connect up 63 external
devices.

16. Physical parts of Buses
 Data Bus: The data bus carries digital information. A data bus is
usually a group of parallel wires connecting different parts of a
circuit. The data bus is connected to the inputs of several gates
and to the outputs of several gates. In general, information may
flow on the bus wires in both directions. This type of bus is
referred to as a bidirectional data bus.
 Control Bus: The physical connections that carry control
information between the CPU and other devices within the
computer. Whereas the data bus carries actual data that is being
processed, the control bus carries signals that report the status
of various devices.
 Address Bus: An address bus is a collection of wires
connecting the CPU with main memory that is used to identify
particular locations (addresses) in main memory. Address bus is
a part of a computer bus.

17. Bus Interconnection Scheme
memory I/O

18. Introduction to Interface
 A boundary across which two independent systems
meet and act on or communicate with each other. In
computer technology, there are several types of
interfaces.
 User interface - the keyboard, mouse, menus of a
computer system. The user interface allows the user to
communicate with the operating system.
 Software interface - the languages and codes that the
applications use to communicate with each other and with
the hardware.
 Hardware interface - the wires, plugs and sockets that
hardware devices use to communicate with each other.

19. Hardware Interface
 Hardware Interface
1. Special-purpose: The keyboard, sound card, mouse,
etc. connectors represent the special-purpose
interfaces. They cannot be used for any other device.
2. Multi-purpose: The parallel port (printer port), serial port,
universal serial bus (USB), and IEEE 1394 FireWire
represent multi-purpose interfaces since they can be
used for various peripheral devices, including data storage
devices.
3. General-purpose interfaces: The slots on the
motherboard, such as PCI and ISA slots, can be used to
connect various devices (via the plug-in cards) and
represent truly general-purpose interfaces

20. Some of the interface commonly
found with recent PCs
 Parallel: The parallel port was originally
created for communicating with the
printer and thus is called a "printer port".
A PC may have at most 3 parallel
ports, which are named LPT1, LPT2, and
LPT3. A parallel port (printer port) female
connector has 25 pins. This 'standard'
parallel port interface can sustain data
rates up to 0.15 MB/s. There are four
more newly created modes, which
enhances parallel port performance.
1. Nibble-mode reverse operation
2. Byte-reverse operation
3. EPP (Enhanced Parallel Port) : 2MB/s
4. ECP (Extended Capability Port)

21. Some of the interface commonly
found with recent PCs
Serial Interface
 If you send bits one at a time, you are
using serial communication. If you send
one extra bit for each 8 bits to make sure
your data got there intact, it is called a
parity bit.
 Two common connector type are used for
serial communication: the 9-pin
connector DB9 and (less often) 25-pin
DB25 connector
 Modern PCs can exchange data over the
serial port at rates up to 115 KB/s, but
this will translate into a maximum
data rate of about only 11.5 KB/s without
parity and 10.5 KB/s with parity

22. Some of the interface commonly
found with recent PCs
USB:
 Set up is very easy. Good
performer. Hot swappable.
Requires Windows 98 and higher.
 Windows 98 supports USB and
there was a limited support for USB
in Windows 95.
 USB is still a serial-type interface
and sends bits one after another...
 In theory, a USB interface can
support up to 127 individual USB
peripherals at one time.
 For practical connection of multiple
devices to the host (root), special
hubs are required. Hubs can have
up to seven connectors to nodes or
other hubs.

23. Some of the interface commonly
found with recent PCs
 IDE/ATA: Set up is moderately difficult. Requires
opening your PC and connecting some cables
inside. Performance is much better than parallel or
USB-devices. The cable has 40 wire connectors in it.
 IEEE 1394 FireWire: Set up is easy. Excellent
performer. Costly. Requires Windows 98 and higher.
The IEEE 1394 standard for the High Performance
Serial Bus, also called Firewire, is a serial data
transfer protocol and interconnection system.

24. Firewire interface
The advantages of the Firewire
interface are:
 High data transfer rate - up to
100 MB/s (800 Mbps), which is
about 60 times faster than USB.
 Supports up to 63 devices (16 -
daisy chained) with cable length
up to about 4.5 m (14 feet).
 Hot-pluggable (like USB).
 Firewire is a plug-and-play bus.
 Firewire cables are very easy to
connect (Like USB).

25. USB vs. IEEE 1394 "FireWire"
Description IEEE 1394 Firewire USB
Maximum number of connected
devices
63 127
Hot-swap? Yes Yes
Plug-and-Play? Yes Yes
Cable length between devices 4.5 m 5 m
Data transfer rate (MB/s) 50/100 1.5/60
PC / Mac Yes / Yes Yes / iMac only
Embedded power line Yes Yes
Peripheral devices
D-Camcorders, D-Cameras,
Set-Top Boxes, HDTV, DVD-
ROM, RAM, Hard Disk drives,
Printers, Scanners
Keyboards, Mice, PC Monitors, Joysticks,
DVD-ROM, RAM, Low-resolution D-
Cameras, Low-speed CD-ROM, RW,
Modems, Printers, Scanners
Relative cost Higher Lower

26. Data Transfer Rates in Serial,
Parallel, ATA, SCSI, Fireware

27. Few Questions
What are the main performance parameters to look for?
 Data transfer rate (DTR) may be the most important
parameter. The data transfer rate is, in general, a function
of the drive's RPM (i.e., 3600, 4200, 5400, 7200, 10000, or
15000) for a given type of drive interface.
 Another important parameter is the total drive's capacity.
How many drives I can install on my computer?
 IDE controllers are limited to 4 devices on a chain (2 on
older ones).
 SCSI controllers are designed for multitasking and can
support from 7 to 15 devices.