[Gllug] SCSI Cards.

[Bruce Richardson]

>>>>>>>>>>>>>>>>>> Original Message <<<<<<<<<<<<<<<<<<

On 1/9/02, 4:27:22 PM, "Paul Brazier" <pbrazier at cosmos-uk.co.uk> wrote 
regarding RE: [Gllug] SCSI Cards. :


> > Well, I'm a SCSI bigot; in particular, IDE doesn't support
> > disconnect-reconnect, which is a pain for non-hard disc devices.

> Why is IDE cheaper and more popular then?
> I guess they're popular because they're cheaper :) but why are they
> cheaper?

SCSI has an intelligent hardware interface, requiring a more complex 
controller on the mobo and more expensive hardware on the hardware 
(iyswim). SCSI presents a comprehensive and standard interface to the 
connected devices.  On a SCSI system the device drivers can simply use a 
standard call (there's a whole SCSI communication protocol) to ask for 
the capabilities of the devices and this is reported back.  There are 
other advantages, such as being able to do concurrent accesses of 
different devices with little or no (perceived) performance penalty.

IDE otoh is little more than a bunch of wires connecting the device to 
the mobo.  The cpu and driver have to do most of the work.  That's a 
simplification and things have improved but it's an ad hoc standard onto 
which things have been crudely grafted.

> Is it purely historical accident and economies of scale (think VHS/Beta)
> or are SCSI systems inherently more expensive to manufacture?

Inherently.

-- 

Bruce

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