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>2. Physical devices</H1
><P
> Flash memory devices come mainly in the form of small, portable
devices often referred to as <EM
>memory sticks</EM
> or
<EM
>keychains</EM
>, and as part of digital
cameras. They are <EM
>non-volatile devices</EM
> which
operate on the principle that electric charges are used to
represent data in binary format. These charges can remain
unchanged almost indefinitely, but changes (such as writing to the
device) limit the life span of the device (100000 writes of 8MB
each).
</P
><P
>
Memory sticks plug directly into a USB-port at the back of your
computer. The power it needs is supplied by the USB-port. It is
sometimes convenient to use a USB-extension cable to bring the
device within easy reach.
</P
><P
> Memory sticks usually have <EM
>write protect
switches</EM
> which should be turned off if you want to use
it as read-write device. If the switch is in the <SPAN
CLASS="QUOTE"
>"on"</SPAN
> position,
the device is <EM
>read-only</EM
>. The devices are
usually equipped with a led (light emitting diode), which
indicates that the device is operational. The led also flickers
while data is being transferred to or from the device.
</P
><P
> Digital cameras use flash memory for image storage. These are
powered by the camera and connected to the computer's USB-port via
an electronic interface. To be able to connect to the computer,
the camera's power must be turned on for the duration of the
interfacing, and should only be turned off after the device had
been unmounted from the computer. It is important to remember that
the device takes power from the camera's battery. The operation
should therefore be terminated as soon as possible.
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