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1. Introduction

The ISA bus may be considered the 'granddaddy' of the modern days buses - PCI, USB, 1394 etc. Developed originally by IBM and included in the first IBM PC computers in the early 1980s. It grew quickly in popularity and was included in all of the motherboards of the IBM compatible systems manufactured at that time.

Why did it become so popular? My guesses are because -
  • it is pretty simple bus
  • it allowed expanding the functionality of the computer system

    With as little as couple of 74xx chips put on a circuit board one hardware designer can make an ISA board, open the box and plug it in the motherboard of their system, and add a new functionality to the computer they use , or control something outside of the computer.

    Countless companies in the 1980s and 1990s made their own ISA boards , which brought new functions to the computer systems of the day. Some big examples developed initially as ISA boards are -

  • sound cards
  • modems
  • network cards

    2. Functionality

    ISA bus is a parallel bus with a separate (not multiplexed) address and data signals. It comes in 2 formats -

  • 8bit , 62 pins
  • 16bit , 98 pins

    The signals on the bus support -

  • physical memory area of up to 16MBytes
  • input/output (i/o) ports area of up to 64kBytes
  • up to 12 interrupt request (IRQ) channels
  • up to 6 direct memory access (DMA) channels

    A standard read/write cycle on the ISA bus is around 250ns , which can be extended with adding 'wait states'.

    The main voltage of the ISA bus is +5v , with also provided additionally - +12v, -12v, and -5v.

    3. Beginning of the end?

    In the 1990s as more powerful microprocessors and operating systems were coming to market , the ISA bus faced challengers.

    In the desktop computers area, there were - IBMs micro channel bus, VESA local bus , and EISA bus. Although faster than the ISA bus, the above choices can not gain more than a limited share of the market.

    In the notebook computers area, it was not possible to fit the ISA bus connector , and one or more ISA cards in the limited space of one notebook computer. The PCMCIA association was created and it adopted much of the signaling of the ISA bus in a much smaller form factor - the 16bit 'pc card' PCMCIA bus.

    Around mid 1990s a new parallel bus was created and started appearing on the PC motherboards - PCI . It promised and delivered much higher speed than the ISA bus.

    Several years later serial buses started appearing - 1394, USB.

    Slowly at first and then faster and faster, the ISA bus slots started disappearing from the PC motherboards.

    4. A new beginning

    One of the areas we , at ARS Technologies work in is to provide the technology and capabilities of using ISA cards outside of the main computer system - on desktop computers , as well as on notebook computers . We have a variety of products, which allow plugging and using of one of more ISA cards . You can find details on our products on - www.arstech.com.

    Who is our technology going to help?

    Case #1 - 10 years ago 'Big Co.' purchased Specific ISA cards and paid several thousand dollars for each one . Joe is a technician in 'Big Co.' with the current assignment to replace the computers at the company with the latest and greatest systems , and still keep working and using the old ISA cards.

    * Solution - Joe is relieved to find that he can still buy the best systems around and use the original ISA card outside of the system.

    Case #2 - Bill is an Engineer at 'Any Inc.' The company has been selling an industrial computer system at the heart of which there is an ISA card . The system was proved again and again during the years and the company do not want to modify much of the ISA hardware, however wants to reduce the total cost of the system. There is a reliable standard desktop system 'Any Inc.' has in mind , but it does not have ISA slots.

    * Solution - Bill can do the integration of the company's ISA card on the new desktop, using one of our hardware products and our software kit.

    Case #3 - Jim is the founder of 'Me Ltd.' , and has found a great chip which he wants to put in a product, which he can control from a notebook . Jim is a skilled designer, familiar with both software and hardware. He is presented with a choice of USB or PCI express, which will require a large portion of his time to get familiar first and then develop a product.

    * Solution - Jim is glad that he can put the chip he found on an ISA card, and control and use it from a notebook , using our hardware products.

    Note: The above cases are composite , and the names have been changed to protect the identity of anyone involved.

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