[Tfug] A/V drives

[Bexley Hall]

Hi, Harry,

--- On Wed, 12/24/08, Harry McGregor <micros at osef.org> wrote:

> You are missing two things.  One, A/V rated drives went out
> about 5 years ago, with the 120GB range drives.  I don't know
> of many, if any AV drives still made.

Actually, A/V drives are still being made.  Hitachi is a
big player -- though they are now geared to STB's, smaller
form factors, etc.  Note that this market has other
pressures that a "single desktop user" market doesn't;
notably, cost, size, power dissipation, etc.  I.e., you
want to *cut* the performance of the device to the point
where it just meets your needs, if possible.

But, whether they represent "current" technology or not is
not related to my question -- if I asked why RMW instructions
represent a boon to machines with *core*, would you feel
the need to tell me "no one uses core anymore"?  :>

(actually, core was in use in the 80's in the shuttle fleet;
I think there is at least one military project which still
relies on core...)

Rather, my question was an attempt to identify characteristics
of A/V drives that made them "different" from "regular" drives.
Having an account of someone who had gone through the regular
drive -> A/V drive transition and his/her observations along
the way would have been *ideal*.
 
> Secondly, A/V rated drives did not throw out thermal
> recalibration, the could delay it slight, hopefully until idle.

Exactly.  Note my reference to *defering* T-cal.

But, this presupposes there is a time when you *know* you
can safely do this without compromising performance!
So, it seems like A/V drives just kicked the can down the
road in the *hope* that there *might* be a more opportune
time to do this, "later".

I.e., this wasn't a "fix".  Rather, it is akin to buying a faster
computer to avoid "making coasters" with early CD writers (buffer
underrun).  There's no *guarantee* that the computer still
won't make coasters -- since it depends on what else the machine
is doing at the time, how much swapping, etc.

OTOH, adding track-size buffers and supporting track-at-a-time
burning was a *real* solution to the coaster problem.

The (original) A/V drive approach is similar to throwing
MIPS at a problem to try to make a non-RT system behave
deterministicly.

Or, doing away with dynamic object creation to try to make
GC-based languages behave deterministicly.

These are just work-arounds, not solutions.

My concern is there are some technologies (not related to
A/V drives at all) that will probably be commercially viable
in 2012 and I need to make an educated gamble as to which
"problems" in those technologies will be surmounted (with time)
vs. those that won't.  And, decide if I want to design with
support for them in mind or sidestep the issue.

This is relevant as many technologies are rushed to market
"crippled" and later refined ("fixed"?).  Witness the CD/DVD
writer issue, wear-leveling in MNOS devices, *new* A/V
drive technology, etc.  I.e., if the upcoming technologies
fall in with this crowd, their future looks promising...
if not, <shrug>

> This has nothing to do with a 24/7 i/o stream, or broadcast
> level A/V or anything to that effect.
> 
> It was more of a marketing ploy to get IDE drives in where
> enterprise class SCSI was the only option.

Understood.  As with the technologies I mentioned (above),
"get your foot in the door" (even if the technology isn't
"quite right", yet) and then fix it once/if it gains
traction in the marketplace.

Moral:  if the technology *can* be fixed, you (I) just
have to make a wager on how *likely* it is to take hold...

Thx,
--don