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Evolution of Computer Buses: From AT to PCI

Explore the history and advancements of computer buses from AT to PCI, detailing features, advantages, and disadvantages of each, including ISA, EISA, VESA, and the widely used PCI bus.

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Evolution of Computer Buses: From AT to PCI

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  1. System Buses Val Grinblat Dan Hummell Ryan McKenica

  2. Introduction • 1980s • More power • Better performance • Enhance operation

  3. PC/XT • Released in 1981 • Extension of the motherboard • Processor and complete control • 62 pins

  4. AT Bus • Limited memory handling • Therefore AT was developed • Two separate oscillators

  5. Physical Differences • A second connector • Backwards compatible • Smooth bridge to the 16-bit data bus

  6. ISA Bus • Industry Standard Architecture • 16-bit addressing limit • Twice as many interrupts and DMA channels

  7. Problems with ISA • Complete access to system resources • No central registry • Limited number of interrupts • Limited number of available ports • Quatech

  8. Micro Channel Architecture (MCA) Bus

  9. 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

  10. 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

  11. 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

  12. 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

  13. Extended Industry Standard Architecture (EISA) Bus

  14. 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

  15. Features • Plug & Play feature • ISA cards work on EISA slots • Addressing Enhancement • 32-bit address bus • Bus width signaling • New transfer modes • Burst mode

  16. Advantages • Backward compatible with ISA • Supports bus mastering for greater efficiency • 32-bit bus width • Interrupt Sharing • Design was open to all manufactures

  17. 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

  18. VESA or VL Bus Video Electronics Standards Association Bus Or Video Local Bus

  19. 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

  20. 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)

  21. Technical Details Cont • VESA bus connector • Two devices on one expansion card • Limited number of VESA devices connected to system board at one time

  22. 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

  23. PCI Bus Peripheral Component Interconnect Bus

  24. 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

  25. 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)

  26. Technical Details Cont • PCI bus connector • Plug and Play compatible • IRQ sharing • PCI Bridge

  27. 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

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