Hi again,
Mark <[EMAIL PROTECTED]> wrote:
> (..)
> As far as I know,
> the only commercial type of memory that keeps its contains, even when the power
> supply is cut off, is FlashRAM. It is used for instance in chipcards etc.
> However, besides FlashRAM, there also other designs of non-volatile memory like
> (..)
Wrong! It's good this fella here did his homework a bit better.
This 'FlashRAM' you mention, IS no Flash-RAM. These chipcards used
as solid-state disk, are either DRAM (mostly temporary use), Flash
EPROM, or battery-backupped SRAM.
The defining difference here is that Flash memory needs to be erased
first, before it can be re-written, and that makes it EPROM memory.
You can't just toggle single bits, like with RAM. In practice, this
is done in 'sectors' (like in xx KB. parts). From the users point
of view, when writing a modified sector to such a solid-state Flash
disk, it might APPEAR as if such a sector was directly overwritten,
but in fact: -the sector might have been written to a different
physical place, erased earlier, or -the (entire!) sector was erased
first, then re-written.
Next to that, Flash (EPROM) memory can only be re-written a limited
number of times. This might as much as 100.000 times, and such
solid-state disks sometimes use sophisticated techniques to
re-arrange sectors, so that if the same area on such a solid-state
disk would be re-written a million times, this might be 'diverted' to
100 different sectors each being re-written 10.000 times. But such a
limit remains.
To overcome this, SRAM becomes the alternative, but needs battery
backup. DRAM might even be used for that, with some extra
refresh-circuitry (might be built in the IC's), and would probably
consume somewhat more power, but that's just practical matters.
All such different types of chipcards might be called differently.
For instance a 'SRAM' card may in fact be DRAM, with self-sustaining
refresh-circuitry, in some low-power arrangement, and...with battery
backup. Or a 'Flash' card might in fact be SRAM, with
very-long-lasting battery, it all comes down to the same thing: in
essence, there simply aren't that many different types of memory, and
as far as I know, Flash-RAM is not among these (prove me wrong).
If you don't agree with this, I suggest you do some reading on actual
existing devices, instead of confusing us all here.
But indeed there are more types of non-volatile memory. I know
another one, maybe 'related' to what you mentioned, called 'bubble
memory'. I don't know what the technical name would be, but that is
how it's called. The idea with this type of memory is this: in a
harddisk/floppy disks, the magnetic areas defining 1's & 0's, reside
on fixed places on a magnetic material, and this material itself is
moved around under some reading/writing circuit.
In 'bubble memory', the magnetic areas containing the 0's and 1's
(the 'bubbles'), are moved instead, so that the reading/writing
hardware can stay in one place, and no parts need to be moving
('solid state'). How this works exactly is a riddle to me, but the
disadvantage of this type of memory was, that the magnetic area's
signalling "1" and "0" needed to be far larger than in the
floppy/harddisk system, making 'bubble memory' large and difficult to
handle devices. That's why they're not, or barely used anymore, only
nice toys for scientists.
There are surely more of such exotic memory types out there, that
grey stuff in our heads would qualify as one...
Greetings,
Alwin Henseler ([EMAIL PROTECTED])
http://huizen.dds.nl/~alwinh/msx (MSX Tech Doc page)
http://www.twente.nl/~cce/index.htm (computerclub Enschede)
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