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List:       opensolaris-discuss
Subject:    Re: [osol-discuss] eSATA works fine?
From:       Erik Trimble <erik.trimble () oracle ! com>
Date:       2011-03-06 22:18:09
Message-ID: 4D740821.9080902 () oracle ! com
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On 3/6/2011 1:51 PM, Orvar Korvar wrote:
> And 6Gbit SATA card needs a driver?


Yes.

You are confusing physical layer (connections and cables) with 
chip-level processing.  Physical layer simply describes how the 
electrical signals are sent, and has nothing to do with the actual 
*content* of those signals.

Each of the following requires some sort of chipset  -  this chipset 
interprets the information it gets from the computer, and converts it 
into the appropriate protocol.  In general, a new PROTOCOL will require 
a new chipset. Certain chipsets will provide backwards compatibility 
(i.e. something handling a 3.0 protocol will likely also understand 2.0 
and 1.0 of that particular protocol), but there is no forwards 
compatibility (i.e. a 2.0 chipset can't understand 3.0 protocol).

SATA
IDE
SCSI
FibreChannel
USB

(and many others).

Chipsets require drivers. Physical layer changes do not.

When determining what protocol is spoken over a physical connection 
between a host controller and a drive (or other peripheral), you look 
for the highest common denominator - thus, a 2.0 controller will speak 
2.0 when talking to a 3.0 peripheral, but will speak 1.0 when talking to 
a 1.0 peripheral.


When wondering whether a device is a chipset or a physical layer change, 
consider this:  does the device actually change the information being 
transported through it, or does it merely change the electrical form of 
the message?

Thus, the following would only change the electrical form:

SAS/SATA port multiplexer/replicators -  they don't change the 
information, merely create a 1-to-many electical signal.
eSATA - it changes the physical connector and cable, but doesn't make 
any other information change
SCSI Ultra2 -> Ultra320 cables - once again, merely the electrical 
signal is changed, not the information format
FC multimode vs singlemode connectors - defines what type of laser 
signal is used to send the FC packets, and thus is just a electrical format


To be perfectly honest, there is one category that is slightly 
confusing: protocol translators, often called "bridges".  You most often 
see this in the "SAS to SATA bridge", though many Host Bus Adapters also 
contain a chip on them that does PCI-E to <something> translation.  
These items are "magic black boxes" - they take an input signal, and 
"magically" convert it to some other.  They do this independent of any 
OS or outside control, and thus, don't need a driver.  Bridges don't 
alter the information content of the signal, but do alter the protocol 
being used - they act as super-translators.



-- 
Erik Trimble
Java System Support
Mailstop:  usca22-123
Phone:  x17195
Santa Clara, CA

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