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Subject: Re: text viewer patch, RAM & battery life
From: for_spam_at_gmx.de
Date: 2003-05-25


hi!

>One thing that puzzles me: doesn't a hard drive have its own built-in
cache?
>Why does it need to spin up every time I read a couple sectors? The
built-in
>cache is for write only?
most hdds have just 2mb cache - and that is (~) the size of memory, your
jukebox
uses for storing mp3 data. i think the cache of the original archos hdd has
this size.
there is no real benefit with this cache regarding "spinups" - if your mp3
buffer is empty,
archos/rockbox firmware requests "another block of ~2mb mp3 data" - so this
is somewhat
just a "read through"

if we want less spinups, i think we would need a hdd with a bigger cache.
I just recognized, that there are toshiba hdds out there which have 16mb
cache (MK-6022GAX/MK-4019GAX).
IMHO, this COULD be interesting - can someone give some comments, if we
would have
"8 times (16mb/2mb)" less spinups with such drive and some "intelligent"
caching with rockbox ?
e.g. when playing an album, rockbox could request 16mb from disk, buffer
just 2mb ( MINUS 200k and other buffers) of them, then disk will spin down and
rockbox could get the "rest" from the remaining hdd-cache. !?!?

STOP - while thinking about this - there is a "problem" left:
HDD is switched to standby mode very soon - this saves a lot of power, but
this invalidates the disk-cache,too. if we want to use the disk-cache, we just
only can switch to idle mode - so, regarding hdd-lifetime this would be good
- but i`m shure this gives WORSE runtime.
(a permanently idle hdd with a disk spinup every 16mb may still need more
average power than a permanently "standby" hdd with a spinup every 2mb - and
this may depend on the hdd model, too...)

regards
roland

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