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ISA BUS
The Industry Standard Architecture or ISA
Pronounced (e-saah) This bus began along with IBM's revolutionary PC/XT released in 1981. However, it was officially recognized as "ISA" in 1987 when the IEEE (Institute of Electrical and Electronics Engineers) formally documented standards governing its 16-bit implementation.
The other bus schemes used in 386 systems were the EISA bus pronuced (eye-saah) bus and IBM’s Micro Channel Architecture or the MCA bus . This first XT bus was intended to allow the addition of system options which could not be fit onto the motherboard. This XT bus was completely under the microprocessor's direct control using the DMA controller, and its addressing width was limited to the 8-bit level of the processor. To make the bus useful, control signals were added to signal interrupts for input/output ports. Bus speed was also limited to match the processor. The PC/XT's 8088 was a one-byte wide 4.77 MHz processor. Thus the XT bus, which required two clock cycles for data transfer, was limited to an unbearably slow (by today's standards) 2.38 Mbps, that could be reduced even further if the system was busy with other tasks.
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ISA BUS
The Industry Standard Architecture or ISA
Pronounced (e-saah) This bus began along with IBM's revolutionary PC/XT released in 1981. However, it was officially recognized as "ISA" in 1987 when the IEEE (Institute of Electrical and Electronics Engineers) formally documented standards governing its 16-bit implementation.
The other bus schemes used in 386 systems were the EISA bus pronuced (eye-saah) bus and IBM’s Micro Channel Architecture or the MCA bus . This first XT bus was intended to allow the addition of system options which could not be fit onto the motherboard. This XT bus was completely under the microprocessor's direct control using the DMA controller, and its addressing width was limited to the 8-bit level of the processor. To make the bus useful, control signals were added to signal interrupts for input/output ports. Bus speed was also limited to match the processor. The PC/XT's 8088 was a one-byte wide 4.77 MHz processor. Thus the XT bus, which required two clock cycles for data transfer, was limited to an unbearably slow (by today's standards) 2.38 Mbps, that could be reduced even further if the system was busy with other tasks.
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