> > Sure, there's always something faster, but that wasn't the point.
> >
> > In a lot of cases you could replace the hard drive in 
> laptops with flash
> > (USB or not) and I doubt most people would even notice.  
> They might notice
> > less noise, more battery life and sticker shock, but speed 
> isn't high on the
> > list these days.
> >
> > I've worked for companies where everyone used laptops & 
> WiFi, a USB 'hard
> > drive' will be faster than that.
> >
> > Tony
> >
>
> Has anyone addressed the problem of max number of writes, 
> though? 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.
> 
> 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). Am I wrong?
> 
> Sean


Max writes has gotten better, but nowhere near what a HDD can do.  For
longevity, I've seen anything from 'lunchtime on Wednesday' to '27 years'
for how long a cell will last.  A million writes shows up a lot, so 1 write
per second gives 11 days before failure.  So 'lunchtime NEXT Wednesday'
then.

Journaling will increase life, and many flash cards claim to do 'wear
levelling', where the controller evens out the writes across the card.
Presumably the controller handles bad blocks as well (like HDD SMART).

One solution is just to put in more RAM so you don't need any virtual
memory.  Flash would probably work ok without that burden.

Someone once mentioned to me that UDF (for rewritable CDs) does wear
levelling too.  I've never bothered to find out if this is actually true, or
was made up by someone in marketing after lunch.

I'm not sure how flash cards handle writes, but that would a limit of the
controller, not the memory itself.

Tony

-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist