On 6/3/07, Gerhard Fiedler <lists@connectionbrazil.com> wrote:
> 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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But once you add more ram windows, just wants even more virtual
memory... have 1 gb of ram? windows wants a 1.5 gig page file. Have 2
gigs? windows wants 3 gigs of virtual memory...  Granted you can turn
it off, like on my desktop with 4 gigs of ram, (3.25 recognized) I
turned off virtual memory, and windows complained for a while. Though
I have yet to have anything that wont run.
-- 
Jonathan Hallameyer
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