System Buses

Val Grinblat

Dan Hummell

Ryan McKenica

Introduction

• 1980s

• More power

• Better performance

• Enhance operation

PC/XT

• Released in 1981

• Extension of the motherboard

• Processor and complete control

• 62 pins

AT Bus

• Limited memory handling

• Therefore AT was developed

• Two separate oscillators

Physical Differences

• A second connector

• Backwards compatible

• Smooth bridge to the 16-bit data bus

ISA Bus

• Industry Standard Architecture

• 16-bit addressing limit

• Twice as many interrupts and DMA channels

Problems with ISA

• Complete access to system resources

• No central registry

• Limited number of interrupts

• Limited number of available ports

• Quatech

Micro Channel Architecture (MCA) Bus

History

• IBM developed MCA bus in 1987• Design began around 1983

– AT bus shows hint of MCA bus design

• First 32-bit bus for the personal computer• Revolutionized design and standard of the bus• Replaced the PC/AT standard for PCs• Inspired by the best ideas from mainframe

computers• IBM patents design to corner the market

Features

• Programmable Option Select– No longer need dip switches, jumpers, and headers

• Small Architecture– Many grounds close to the high frequency digital

signals– Smaller PCs

• Multitasking• 32-bit bus width• First plug & play board

Advantages

• Microprocessor Speed vs. Bus Speed– 8 Mhz Bus Clock Signal lock– 10 Mhz Capability

• Higher speed than ISA• Extra data lines:16 more data lines for 32 bits total• More address lines:4 gigabytes address memory• Channels for improved audio and video• Smaller mount components and expansion boards• FCC Certification easy to attain

– Every fourth pin had electrical ground

Disadvantages

• Obsolete• Costly for manufactures and users to

upgrade from PC/AT-based PCs• Not backward compatible with ISA-based

boards• IBM had total control over architecture• Bus speed not fast enough for modern

processors and PCs

Extended Industry Standard Architecture (EISA) Bus

History

• Introduced in 1998• “Gang of Nine”

– Nine companies united to develop a design to match IBM’s MCA bus

• Improvements based on MCA– Compatible with ISA-based systems– Not patent to one company

• Molded from the AT bus design

Features

• Plug & Play feature

• ISA cards work on EISA slots

• Addressing Enhancement– 32-bit address bus

• Bus width signaling

• New transfer modes– Burst mode

Advantages

• Backward compatible with ISA

• Supports bus mastering for greater efficiency

• 32-bit bus width

• Interrupt Sharing

• Design was open to all manufactures

Disadvantages

• More expensive than other systems

• Few EISA-based cards available

• Performance is lower than more modern, popular buses such as the VESA local bus and PCI

• Not widely used

VESA or VL Bus

Video Electronics Standards Association Bus

Or

Video Local Bus

Brief History

• Developed by the Video Electronics Standards Association

• To replace slow ISA bus for video components and high-speed devices

• Can be used a local video bus or an expansion bus

Technical Details

• Data width 32 bits

• Bus speed 33MHz

• Throughput 250 MB/sec

• Transfer rate 8 times faster then the ISA bus

• Bus connector original ISA slot plus additional VESA slot (see figure)

Technical Details Cont

• VESA bus connector

• Two devices on one expansion card

• Limited number of VESA devices connected to system board at one time

What happen to the VESA bus?

• It had a good design and good features

• Plans from VESA for a 64-bit version of the bus for the Pentium processor

• However, the PCI bus become more popular when the Pentium processor became the standard processor

PCI Bus

Peripheral Component Interconnect Bus

Brief History

• Developed in 1993 by the Intel Corporation

• Originally design for better graphics capabilities on Intel computers

• Has become the standard general-purpose bus

• Used in PCs and Macintosh computers

Technical Details

• Data width 32 bits

• Bus speed 33 MHz

• Throughput 265 MB/sec

• Can run at speeds different then the CPU

• Short slot length then the both the ISA and VESA bus (see figure)

Technical Details Cont

• PCI bus connector

• Plug and Play compatible

• IRQ sharing

• PCI Bridge

Where is the PCI bus today?

• Standard in most all PCs sold today

• Still the standard general-purpose bus

• Not often used for video adapters since development of the AGP bus