[Wine] Portable Wine

Martin Gregorie martin at gregorie.org
Sun Sep 25 05:55:27 CDT 2011

On Sat, 2011-09-24 at 18:49 -0500, SpawnHappyJake wrote:

> Also, constantly reading and writing to a thumb drive is hard on the
> flash cells and will kill your thumb drive. I recommend copying it off
> the thumb drive to a temporary location on your friend's computer, and
> then copying it back on when you are done, and delete the temp folder.
I used to think that until I read up on wear levelling.

All flash cards have a lifetime that's determined by two parameters:
chip design life expressed as write cycles
the design life of the package expressed as insert/remove cycles

Cheap cards may be designed for as few as 10,000 write cycles while
premium cards are typically designed for 100,000. Most card contacts are
designed for 20,000 insertions and removals. The lifetime of an SD card
is unaffected by the number of times it is read. Writing involves a
chemical change to the chip: each time a bit in the chip is written it
is degraded slightly. The material its made of is specified to last at
least the design life before it degrades sufficiently to become
unreliable. Calculations show that a good quality card is likely to be
lost or trodden on before either the chip or the contacts wear out. 

This calculation assumed that the card was a 2GB SD card organised into
4K blocks and that it has a design life is 100,000 write cycles per
memory cell and 20,000 insertion cycles for the contacts. These are
typical figures for a premium quality card. 

The application, a real one involving logging GPS data as it is
received, writes a 40 byte line to a log file once a second. If a
premium SD card is used, it will take 303 thousand years before the
cells in a memory block wears out. 

I also assumed that the card would be removed from the recording device
and read into a PC every day (2 insertion/removal cycles per day). The
card should withstand this for 27 years.

As I said: unless the card is mistreated or faulty, you're likely to
lose or damage it before it wears out. 

Don't believe me? The specs of a decent SD card, e.g. Crucial or
SanDisk, are on the 'net, so download them, read up on how the cards are
organised and how wear levelling works (both are well described in
Wikipedia) and do the calculations for yourself.


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