Sean Breheny wrote:

> Has anyone addressed the problem of max number of writes, though? 

Yes. Windows XPe:
<http://msdn2.microsoft.com/en-us/embedded/aa731409.aspx>. I've also seen
distros for Linux that offer solutions for this; just don't have any links
handy.

> Most modern OSes use virtual memory extensively. Having to cache the
> flash drive to prevent memory cell wear-out due to writes defeats the
> purpose of virtual memory, since you would need almost as much cache
> memory (I think) as the virtual memory size.

Right. So you just need to work without virtual memory and do most of the
temp stuff in RAM, which means that you need enough RAM. But once you spend
the money on a Flash disk of the necessary size for a typical PC, the
additional money for the necessary RAM is little more than pocket change :)

There is also a tradeoff between having more RAM and using up more Flash
write cycles for temp stuff. This tradeoff depends on what you want or
need.

> Also, I thought that flash achieved its relatively high write speed by
> requiring block writes. So, in order to write 10 bytes you have to write
> a whole block, which may take milliseconds, but yields a high throughput
> because of the size of a block (EEPROM took milliseconds to write 1
> byte, flash takes milliseconds to write several kilobytes, but neither
> can complete any size write operation in less than milliseconds). 

Correct, but with suitable caching, I don't think that any of this is
noticeable unless you're really needing high throughput writes. Harddisk
head positioning is also not instantaneous, and just as you need to write a
whole block if you want to write 10 bytes, you need to move the head to the
target location even if you only want to write 10 bytes. I didn't test it,
but I'd say for writing 10 bytes, a typical Flash is way faster than a
typical harddisk on average. 

Gerhard

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