11/05/99

80,000 foot view of common IBM PC expansion buses:

By David A. Ranch
http://www.ecst.csuchico.edu/~dranch

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This is a big question.  I recommend that you search on the
web and try to get the specs since I don't know all the 
details.  I can give a few hints though:

ISA	- originally 8bit and then 16bit running at 8Mhz

MCA	- A proprietary 32-bit bus from IBM.  After IBM
	  watched the industry accept the ISA bus for
	  no royalities, they made one that people had
	  to license and thus, the industry never
	  accepted it.  MCA was an excellent bus 
	  but it never caught on.

EISA	- downward compatible with ISA but supported 32
	  bit.  EISA cards are configured via their own
	  special EISA diskette and the data was stored
	  in a private section of the CMOS setup.  
	  It was a pain.

VLB	- New extention to the 16bit ISA bus to give
	  32bit at < 50Mhz.  This was the first 
	  "LocalBus" setup for video, etc and was 
	  very fast in comparison of ISA, MCA, EISA.

PCI	- Whole new "local bus" from Intel that could 
	  allow more than VLB's 3 slot maximum.  Usually is
	  32bit though there is a newer 64bit extention.
	  It also runs at 33Mhz but is overclockable
	  if the PCI cards allow it.

AGP	- A new local bus from Intel for video.  Comes
	  in 1x, 2x, and 4x speeds.  It believe it runs 
	  at 1/2 the processor speed.  Its considerably
	  faster than PCI but can't be shared like PCI.
	  Thats why its ONLY video (the heaviest I/O
	  user there is).