X86 Computer Bus Subsystems IBM PC/XT Architecture ('82, '83)
X86 Computer Bus Subsystems IBM PC/XT Architecture ('82, '83)
X86 Computer Bus Subsystems IBM PC/XT Architecture ('82, '83)
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Plug and Play<br />
– Each New Adapter May Require:<br />
• DMA Channels<br />
• IRQ Lines<br />
• Parallel I/O Addresses<br />
– Adding New Adapter to ISA <strong>Bus</strong> Can Cause Conflicts<br />
1) User Must MANUALLY Change DIP Switch<br />
2) Automatic Configuration<br />
– “Plug and Play”<br />
• “Standard” Developed by Intel/Microsoft<br />
• Adapters Contain Special Registers for OS Query<br />
• Adapters Accept Commands to Change Values or Deselect<br />
• Need a PnP Aware ROM-BIOS (sequence during boot-time)<br />
Microchannel <strong>Architecture</strong> (MCA)<br />
Proprietary <strong>IBM</strong> Adapter <strong>Bus</strong> - 1987<br />
• 8.33 MHz, 16-bit AT <strong>Bus</strong> Causes Sever I/O Bottleneck<br />
– Lots’ of Graphics versus Character Mode Data<br />
– 25 MHz 80386DX Available – CPU BW Far Exceeds <strong>Bus</strong> BW<br />
• MCA – 10 MHz at Selectable 8, 16, 32 bits<br />
• Totally Incompatible with ISA<br />
• <strong>IBM</strong> Proprietary – Must License to Use<br />
– Pay <strong>IBM</strong> $$$$ to Make Adapters<br />
• 9 Popular <strong>Computer</strong> Manufacturers Form Consortium<br />
– “Gang of Nine” – EISA is Born!<br />
• MCA is no longer popularly used<br />
4
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