[Pc_Support] Serial Attached SCSI (SAS) -- WAS: Vista EULA

[Bryan J. Smith]

> ahh got ya.  nice to know.  so in bigger environments and places
> with extremely heavy traffic going with the newer SCSI is the
> way to go.

First off, parallel has been _dead_ as a viable storage interconnect
for some time.

Secondly, the concept of 1 dedicated device per storage channel has
been taking over for years now.  Back when Integrated Drive
Electronics (IDE) and AT Attachment (ATA) were new, you still had
Programmed I/O (PIO), and early Single/Multiword (8/16-bit) Direct
Memory Access (DMA) did not do error checking.  But once the newer
ATA standards hit with UltraDMA modes and CRC, ATA started to show
how powerful it could be for burst transfers.  Which brings me to ...

Third, more and more intelligence in the OS and controller options. 
OSes started doing better buffering and caching, especially with
increased memory.  Intelligent controllers started off-loading
queuing and caching to their on-board ASIC/uCs.  In fact, when doing
raw block transfers with non-blocking I/O, including RAID-0, 1 and
10, an ASIC+SRAM with ATA drives just smacks everything silly.

Now the SCSI vendors were just smart and realized that they needed a
serialized version.  It actually solved a _lot_ of issues they had
with parallel SCSI in general.  That includes multitargetting with
SAS switches and storage subsystems.


-- 
Bryan J. Smith   Professional, Technical Annoyance
b.j.smith at ieee.org    http://thebs413.blogspot.com
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