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Industry standard architecture (ISA), Peripheral component Interconnect (PCI) Accelerated Graphics port (AGP) Plug-and-Play devices – SCSI concepts USB architecture


l Buses evolved around data path and speed

l Local bus (system) and expansion bus (ISA)

l Buses carry electrical power, control signals, memory addresses, and data

l On-board ports, connectors, and riser slots

These are “slots” on the motherboard


ISA – Industry Standard Architecture

PCI – Personal Component Interconnect

EISA – Extended ISA

SIMM – Single Inline Memory Module

DIMM – Dual Inline Memory Module

MCA – Micro-Channel Architecture

AGP – Accelerated Graphics Port

VESA – Video Electronics Standards Association

PCMCIA – Personal Computer Memory Card International Association (not just memory!)



AGP slot

PCI slot

ISA slot

Industry Standard Architecture(ISA)

pronounced “eye-es-eh”


Originally introduced in the IBM PC (1981) as an 8 bit expansion slot

Runs at 8.3 MHz with data rate of 7.9 Mbytes/s

16-bit version introduced with the IBM PC/AT

Runs at 15.9 MHz with data rate of 15.9 Mbytes/s (?)

Sometimes just called the “AT bus”

Today, all ISA slots are 16 bit


Parallel, multi-drop

Used for…

Just about any peripheral (sound cards, disk drives, etc.)


In 1993, Intel and Microsoft introduced “PnP ISA”, for plug-and-play ISA

Allows the operating system to configure expansion boards automatically

Form factor

Large connector in two segments

Smaller segment is the 8-bit interface (36 signals)

Larger segment is for the 16-bit expansion (62 signals)

8-bit cards only use the smaller segment



Extended ISA

Design by nine IBM competitors (AST, Compaq, Epson, HP, NEC, Olivetti, Tandy, WYSE, Zenith)

Intended to compete with IBM’s MCA

EISA is hardware compatible with ISA


Micro Channel Architecture

Introduced by IBM in 1987 as a replacement for the AT/ISA bus

EISA and MCA have not been successful!

Configuration is not automated

ISA bus does not manage system resources, as do USB and PCI bus controllers

ISA device must request system resources at startup

Peripheral Component Interconnect (PCI)

Also called “Local Bus”


Developed by Intel (1993)

Very successful, widely used

Much faster than ISA

Gradually replacing ISA


Parallel, multi-drop

Used for…

Just about any peripheral

Can support multiple high-performance devices

Graphics, full-motion video, SCSI, local area networks, etc.


64-bit bus capability

Usually implemented as a 32-bit bus

Runs at 33 MHz or 66 MHz

At 33 MHz and a 32-bit bus, data rate is 133 Mbytes/s

PCI bus

Currently the standard I/O bus

Uses an interim interrupt between PCI card and IRQ line to the CPU

PCI bus controller

Manages the PCI bus and expansion slots

Assigns IRQ and I/O addresses to PCI expansion cards

Use Device Manager to see which IRQ has been assigned to a PCI device

Accelerated Graphics Port (AGP)

For AGP Diagram refer your text Book


First appeared on Pentium II boards

Developed just for graphics (especially 3D graphics)


Parallel, point-to-point (only one AGP port / system)


Data rates up to 532 Mbytes/s (that’s 4x PCI!)

The Accelerated Graphics Port (also called Advanced Graphics Port) is a high-speed point-to-point channel for attaching a graphics card to a computer’s motherboard, primarily to assist in the acceleration of 3D computer graphics.

· Some motherboards have been built with multiple independent AGP slots. AGP is currently being phased out in favor of PCI Express.

· Type of video card that has its own processor to boost performance

· Features reduce burden on motherboard CPU, (eg, MPEG decoding, 3-D graphics, dual porting, color space conversion, interpolated scaling, EPA Green PC support, digital output to flat panel display monitors, application support for high-intensity graphics software)

Advantages over PCI

Texturing: Also called Direct Memory Execute mode, allows textures to be stored in main memory.

Throughput: Various levels of throughput are offered: 1X is 266 MBps, 2X is 533 MBps; and 4X provides 1.07 GBps.

Sideband Addressing: Speeds up data transfers by sending command instructions in a separate, parallel channel.

Pipelining: Enables the graphics card to send several instructions together instead of sending one at a time

Versions of AGP

AGP 1x

A 32-bit channel operating at 66 MHz resulting in a maximum data rate of 266 megabytes per second (MB/s), doubled from the 133 MB/s transfer rate of PCI bus 33 MHz / 32-bit; 3.3 V signaling.

AGP 2x

A 32-bit channel operating at 66 MHz double pumped to an effective 133 MHz resulting in a maximum data rate of 533 MB/s; signaling voltages the same as AGP 1x;

AGP 4x

A 32-bit channel operating at 66 MHz quad pumped to an effective 266 MHz resulting in a maximum data rate of 1066 MB/s (1 GB/s); 1.5 V signaling;

AGP 8x

A 32-bit channel operating at 66 MHz, strobing eight times per clock, delivering an effective 533 MHz resulting in a maximum data rate of 2133 MB/s (2 GB/s); 0.8 V signaling.


AGP Pro is a extention to the standard AGP connector and slot on both sides to provide additional power to an AGP card.
It comes in two flavors, AGP Pro110 provides for 50-110W of power and requires two adjacent PCI slots for cooling. AGP Pro50 provides for 20-50W of power and requires a single adjacent PCI slot for cooling.

64 bit AGP: A 64-bit channel. Used in high end professional graphic cards.

Small Computer Systems Interface (SCSI)

pronounced “scuzzy”


Developed by Shugart Associates (1981)

Originally called Shugart Associates Systems Interface (SASI, pronounced “sassi”)

Scaled down version of IBM’s System 360 Selector Channel

Became an ANSI standard in 1986

Used for…

Disk drives, CD-ROM drives, tape drives, scanners, printers, etc.


Parallel, daisy chain

Requires terminator at end of chain

Versions (data width, data rate)

SCSI-1, Narrow SCSI (8 bits, 5 MBps)

SCSI-2 (8, bits 10 MBps)

SCSI-3 (8, bits, 20 MBps)

UltraWide SCSI (16 bits, 40 MBps)

Ultra2 SCSI (8 bits 40 MBps)

Wide Ultra2 SCSI (16 bits, 80 MBps)


Connection of the PC to Telephone

The USB provides a ubiquitous link that can be used across a wide range of PC-to-telephone interconnects.

Ease of use

Hot plug

Port expansion

The lack of a bi-directional, low-cost, low-to-mid speed peripheral bus has held back the creative proliferation of peripherals such as telephone/fax/modem adapters, answering machines, scanners, PDA’s, keyboards, mice, etc.





dynamically attachable serial interface

consistent with the requirements of the PC platform of today and tomorrow

Wide range of workloads and applications

Suitable for device bandwidths ranging from a few kb/s to several Mb/s

Supports isochronous as well as asynchronous transfer types over the same set of wires

Supports concurrent operation of many devices (multiple connections)

Supports up to 127 physical devices

Supports transfer of multiple data and message streams between the host and devices

Allows compound devices (i.e., peripherals composed of many functions)

Lower protocol overhead, resulting in high bus utilization

Universal Serial Bus (USB) is a serial bus standard to interface devices to a host computer. USB was designed to allow many peripherals to be connected using a single standardized interface socket and to improve the plug-and-play capabilities by allowing hot swapping, that is, by allowing devices to be connected and disconnected without rebooting the computer or turning off the device. Other convenient features include providing power to low-consumption devices without the need for an external power supply and allowing many devices to be used without requiring manufacturer specific, individual device drivers to be installed.

USB 1.0

  • USB 1.0: Released in January 1996.
    Specified data rates of 1.5 Mbit/s (Low-Speed) and 12 Mbit/s (Full-Speed). Did not anticipate or pass-through monitors. Few such devices actually made it to market.
  • USB 1.1: Released in September 1998.
    Fixed problems identified in 1.0, mostly relating to hubs. Earliest revision to be widely adopted.

USB 2.0

  • USB 2.0: Released in April 2000.
    Added higher maximum speed of 480 Mbit/s (now called Hi-Speed). Further modifications to the USB specification have been done via Engineering Change Notices (ECN). The most important of these ECNs are included into the USB 2.0 specification package available from


    • Mini-B Connector ECN: Released in October 2000.
      Specifications for Mini-B plug and receptacle. These should not be confused with Micro-B plug and receptacle.
    • Errata as of December 2000: Released in December 2000.
    • Pull-up/Pull-down Resistors ECN: Released in May 2002.
    • Errata as of May 2002: Released in May 2002.
    • Interface Associations ECN: Released in May 2003.
      New standard descriptor was added that allows multiple interfaces to be associated with a single device function.
    • Rounded Chamfer ECN: Released in October 2003.
      A recommended, compatible change to Mini-B plugs that results in longer lasting connectors.
    • Unicode ECN: Released in February 2005.
      This ECN specifies that strings are encoded using
      UTF-16LE. USB 2.0 did specify that Unicode is to be used but it did not specify the encoding.
    • Inter-Chip USB Supplement: Released in March 2006.
    • On-The-Go Supplement 1.3: Released in December 2006.
      USB On-The-Go makes it possible for two USB devices to communicate with each other without requiring a separate USB host. In practice, one of the USB devices acts as a host for the other device.
    • Battery Charging Specification 1.0: Released in March 2007.
      Adds support for dedicated chargers (power supplies with USB connectors), host chargers (USB hosts that can act as chargers) and the No Dead Battery provision which allows devices to temporarily draw 100 mA current after they have been attached. If a USB device is connected to dedicated charger or host charger, maximum current drawn by the device may be as high as 1.5 A. (Note that this document is not distributed with USB 2.0 specification package.)
    • Micro-USB Cables and Connectors Specification 1.01: Released in April 2007.
    • Link Power Management Addendum ECN: Released in July 2007.
      This adds a new power state between enabled and suspended states. Device in this state is not required to reduce its power consumption. However, switching between enabled and sleep states is much faster than switching between enabled and suspended states, which allows devices to sleep while idle.
    • High-Speed Inter-Chip USB Electrical Specification Revision 1.0: Released in September 2007.

USB 3.0

On September 18, 2007, Pat Gelsinger demonstrated USB 3.0 at the Intel Developer Forum. USB 3.0 is targeted at ten times the current bitrate, reaching roughly 4.8 Gbit/s (600MB/s) by utilizing two additional high-speed differential pairs for “Superspeed” mode, and with the possibility for optical interconnect.[28][29] The two new differential pairs make the cable about as thick as an ethernet cable and provide full-duplex transfers.[30] The USB 3.0 specification was 90% complete as of August 13, 2008[31] and commercial products are expected to arrive in 2009 or 2010.[32] USB 3.0 is designed to be backwards-compatible with USB 2.0 and USB 1.1 and employs more efficient protocols to conserve power[28] while increasing the maximum power available for connected devices.[30]

Access Time

w Seek Time

n Time required to move the read/write head to the proper track

w Latency Time

n Rotational delay

n Time until head is over correct track

w Times measured in ms

Categories: EC1003 UNIT V
  1. mohan
    December 25, 2008 at 4:25 PM

    sir, can you give me the answers for the unit test question papers…

  2. Rinks
    December 26, 2008 at 5:34 AM

    sir could yu pls get me sum of d imp ques in al d units whic would b enough for d modals as wel as semesters?? do mail me d same at “rinkeshbafna@rocketmail.com”

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