[sf-lug] Rick's explanation of his internet setup.

Adrien Lamothe alamozzz at yahoo.com
Tue Jan 3 19:51:59 PST 2006

>I sort of threw into "I/O" just about everything else other than the
>aspects I mentioned:  disk access, various actual I/O ports, memory
>access.  But I meant primarily disk (mass storage subsystem) 
>performance -- given that gamers _are_ smart enough to ensure adequate amounts of
>fast RAM on a fast memory bus.

The computer industry has been going the way of the 
automotive industry - do things "good enough", but "cheap".
Hardly anyone uses SCSI anymore, many people think SATA is
just as fast, because of certain specs the vendors flaunt
to encourage such mis-perception. However, what they fail
to mention is that SCSI devices have a SCSI controller, and
that a SCSI controller is a separate slave microprocessor
that handles the bulk of data I/O. When the CPU/operating
system wants data from a SCSI device, the SCSI controller
is given some basic instructions:  1. where to find the data I want. 
2. a location to put that data.
The SCSI controller goes about doing its work and transfers
the data directly to memory, using a DMA channel to do so.
When the data transfer is complete, the SCSI controller
signals the CPU that "hey, I'm done, the data you wanted
is now where you wanted it." What does this mean to system
performance? It means the CPU is free for other activity
during a large portion of the data transfer. Under IDE,
the CPU is occupied for the entire period of data transfer.
While this is a slightly simplified description, it does
describe the architecture and salient differences.
For most people's computer usage, this performance gain
is not enough to justify spending more for SCSI, so people
settle for "good enough."

By the way, SCSI is still expensive. So, how much are you
willing to pay for a "smoking" system? Depends on your
requirements and the economic costs vs. benefits.

- Adrien

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