

Tim Bray on the iPad: Memory Matters - scw
http://www.tbray.org/ongoing/When/201x/2010/04/05/Memory-Matters

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anotherjesse
Does anyone know why apple only included 256MB memory?

The lack of ram means that in-memory cache for the browser is limited (to
zero?), which limits performance.

The cost of ram seems so small (a few dollars per GB in bulk) to a software
developer - is the cost energy consumption or ???

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derefr
It's not RAM in the form of SIMMs or DIMMs, though, it's RAM embedded into the
chip (like everything else; the A4 is a System-on-a-Chip), meaning that it's
basically an L3 cache: it suffers from heat dissipation and placement issues
just like the L1 and L2 caches do.

The real question is whether Apple has designed the A4 with an external memory
bus that's currently not being put to use, and which would allow for future
expansion in the "iPad 4G·S" or somesuch equivalent. It would actually be a
very clever game-theoretic strategy to constrain the memory at first.

If Apple had instead released this first iPad _without_ multitasking but
_with_ 2GB of RAM (or even more; it could certainly all fit in the case, and
RAM doesn't really impact battery life) developers would be sloppy and use as
much of it as they wanted, disallowing their apps from ever being multitasked
in the future.

However, constraining memory to 256MB at first forces developers to write apps
that only use that much. Later, Apple can release the 2GB model, and it would
suddenly be possible to multitask 8 or more of the 256MB-model apps at once.
(Of course, also making provisions for new "fat" 2GB apps.)

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mikepurvis
"A4 with an external memory bus"

I'm really completely out of my depth here, but if that were the case, I
wonder if you could mostly eliminate the Flash memory, except for the OS.
Would there be cost or performance advantages in doing so? I mean, it would
suck to lose 64GB worth of stuff if the battery ever died, but the battery's
locked in there, and you could put in some kind of backup button-battery...
maybe that added complexity would negate any cost or performance advantages.

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rbranson
Besides being cheaper, flash memory is significantly more compact.

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mikepurvis
Oh... yeah, I guess that's right. I'm still thinking in terms of the old Palm
devices that used RAM rather than flash. But that was a different time.

