In simple terms, an SRAM card has its own battery in the card and uses a type
of chip that requires constant refreshing in order to retain the data. The
battery in the card usually lasts about two years, so the manufacturers
recommend replacing it once every year. If the battery goes, so does the
data. The chips will retain the data for a few minutes, though, time enough
to replace the battery when need be. An SRAM card never wears out and
theoretically could last forever, needing only a new battery every year or
two.
A Flash card does not have its own battery and relies on the device you use
it with to provide the power. The chips in a Flash card are physically
modified whenever you write data to the card. Eventually, the chips get "used
up" and you can no longer write new data to the card. The number of disk
writes that can take place before this happens is in the hundreds of
thousands, so for most normal use a Flash card has a life of several years.
Flash cards are generally less expensive than SRAM cards.
The reason why Flash cards are not recommended for the OmniGo 100 is that
they demand a significant electrical charge to initialize. There's actually a
driver on the OmniGo that supports many Flash cards, and if your batteries
are brand new, you might successfully insert and use a Flash card -- for a
while. However, when the batteries in the OmniGo are down by even one third
or so, they might not have enough power to initialize the card, and that
could result in data loss both on the card and on the OmniGo itself.
There are some new low-power Flash cards being introduced to the marketplace
now that may work around the power issue. That's what you're seeing
advertised as Flash for the OmniGo. As of this writing, HP has not certified
those cards for the OmniGo, so your warranty for their use resides with the
card manufacturer.
Steve