# RE: HARI: Question regarding byte (column?) versus word striping

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> -----Original Message-----
> From: Devendra Tripathi [mailto:devendra.tripathi@xxxxxxxxx]
>
>
> I am getting somewhat confused on this isse. Could someone
> give a pointer
> to where the
> concept of "lane", "column" and "striping" are detailed ?

hi - I don't know where they detailed, but I'll
take a shot at it here...

(warning: the following metaphors seem natural to a Southern
California native - I hope they do to everyone else!-)

Lane
----
Think of a single lane road. Cars on this road pass any
point on the road one at a time - in a sort of serialized
fashion.

Now, widen the road to four lanes. Four times the number of
cars can now get from one point to another in the same time
period. Yet the cars still generally travel in a serialized
fashion to their destination.

Rather than call this four roads, we naturally refer to it as
a 'four lane road', since it is still a link between two
points - it is just wider.

Similarly, HARI proposes a four lane link, since it is just a
wider link between two devices. Seems more natural and less

Striping
--------
Think of a one lane road making a transition to a four lane
road. At this transition is a traffic cop directing the each
car as it passes into the correct lane. The cop could choose
to send one car to each lane in turn, or send a group of cars
to each lane in turn.

(I'm guessing the term 'striping' comes from the stripe that
delineates the lanes, but that's just a guess ;-)

In HARI, the question is whether we send one byte to each lane
in turn, or whether we send four bytes to each lane in turn -
byte striping or word striping.

Column
------
This one is a little counter-intuitive relative to our road
experience.... but think of four cars travelling abreast on
our four lane road. Across the four lanes, these four cars
represent a column.

In HARI, four bytes across the four lanes is considered a
column. This is why 'column-striping' is somewhat synonymous
with byte-striping - I think that some folks feel that 'column-
striping' is a better term because it is more descriptive
of the situation.

I hope this helps a little, and please do correct me if I
have stretched a metaphor a little too far!-)

- js

jeff stai, QLogic corp.
3545 harbor blvd, costa mesa, ca 92626
714-668-5425vm, 714-668-5095fx
j_stai@xxxxxxx  http://www.qlc.com/

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