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Comment by bambax | Hacker News Reader

I don't understand why mobile devices have so little "RAM" when they have fixed storage in the tens of Gos that is effectively made of memory chips...?

What is the difference between the two kinds of memory, and why isn't more RAM added? Is it a cost problem? a size problem? both? Or is the CPU not capable of addressing more RAM...?

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Price for performance and quality. RAM is higher performance memory that does not degrade over time and thus cost a lot more. Flash memory is slower and has a limited number of writes per bit. I think that has something to do with the decisions made.

Still, I find it hard to fathom why the iPad only has 256MB of RAM, for example -- the cost difference between 256 and 512 MB of RAM is very small. More RAM will consume marginally more power, but that doesn't seem a convincing reason either.

I hadn't considered that before. You would figure that it would be pretty easy to add virtual memory to ios.

But then it would have to swap, the user experience would suffer unpredictably, Steve Jobs would strangle the engineer responsible and the feature would never see the light of day.

"Virtual memory" does not imply "it would have to swap"; indeed, the iPhone does have virtual memory, and each application has its own virtual address space.

Indeed, all memory management in iOS is virtual, they just don't use a pagefile on any iOS devices. If the pager's not built in already and just turned off, I'm sure it'd be a very simple thing to add.

As others have pointed out iOS does have virtual memory. As to why it doesn't use a swap file probably the a reason is that flash memory has a limited number of read-write cycles, probably way more than you could ever use under normal usage but with paging stuff to and from flash all the time you might reach the limits much faster.

That may be a factor, but I think it's much more likely to be related to interface fluidity. People swap to SSDs on desktops/laptops without significant issue.

I believe Android uses a similar scheme: virtual memory but no pagefile. Is there a way to turn on paging on Android?

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