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From: gerardka@hobbes.ism.isc.com (Gerard Kam)
Newsgroups: comp.sys.ibm.pc.hardware
Subject: Re: SCSI confusions, help please!
Message-ID: <1991May22.021133.24448@ism.isc.com>
Date: 22 May 91 02:11:33 GMT
References: <TIMS.91May16115641@infidel.infidel.lanl.gov>
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In article <TIMS.91May16115641@infidel.infidel.lanl.gov> tims@infidel.lanl.gov (Tim Sullivan) writes:
	<deleted>
>So what is wrong here? What is it about SCSI controllers that can
>support price differences so large? What does a $1600 controller do
>that a $100 controller doesn't do? There must be something I don't
>understand. 
>
	The "SCSI controller" is more correctly called a SCSI host
	adapter.  Its function is to provide an interface between the
	CPU system bus (ISA, EISA, Microchannel) and the SCSI bus.

	The host adapter can be so simple as to require complete CPU
	operation for control and I/O (programmed I/O).  A step up
	would have direct memory access (DMA) data transfers.
	The fancy ones have on-board processors and large buffers.
	These are very common on VME and Multibus SCSI adapters.
	Since EISA and Microchannel are also multi-processor buses,
	there are a few intelligent SCSI adapters for those also.

	Gerard