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From: crouse@eng.umd.edu (Gil Crouse)
Newsgroups: comp.sys.ibm.pc.hardware
Subject: Re: EISA vs. ISA
Message-ID: <1990Dec14.024322.3967@eng.umd.edu>
Date: 14 Dec 90 02:43:22 GMT
References: <51097@eerie.acsu.Buffalo.EDU> <obO0GSq00UzxA3Q64_@andrew.cmu.edu>
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In article <obO0GSq00UzxA3Q64_@andrew.cmu.edu> jc58+@andrew.cmu.edu (Johnny J.
Chin) writes:
>Excerpts From Captions of netnews.comp.sys.ibm.pc.hardware:
>13-Dec-90  Re: EISA vs. ISA               Robert J Miskines@ubvmsd (1877)   
>>ISA is the 16-bit bus those of us with AT/Compatibles are familiar with. 
>>EISA is a 32-bit bus, where the first part of the bus is ISA-compatible
>>if im not mistaken... But, it has an additional set of 'fingers' for an 
>>additional 16 bits to go through.. I believe this is similar to the 8/16 bit 
>>slots in an AT/Compatible - the first section of the 16-bit bus is
>>8-bit compatible.. you can plug 8-bit cards into it. If your card has the    
>>additional 'finger set' for 16-bit work, even better.. EISA is the same way. 
>>It will take already existing 8 and 16 bit cards, as well as 32-bit. 
>
>Sorry, but I think that you are wrong.  EISA is not physically similar to ISA.
>EISA looks like ISA, but the 32-bit section (pins) run in between the ISA pins
>and are connected below the ISA pins.  EISA pin connections are also narrower
>than ISA.  From my last comparison, ISA pins are twice as wide as EISA.  Don't
>ask me how, but the connections work.  EISA slots are the same length as the
>16-bit ISA slots.
>
>*** SOMEBODY PLEASE CORRECT ME IF MY MEMORY FAILS ME NOW. ***
>
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Sorry, Mr. Chin but the original poster is correct.  An EISA bus is downward
compatible with ISA cards.  The EISA connectors are narrower than ISA
connectors and run between them as you describe, but both will function.


Gil Crouse
crouse@eng.umd.edu
(301) 405-1140