[Leica] Digital questions . . . .

[firkin at ncable.net.au (Alastair Firkin)]

Great explanation: should I therefore NOT buy 4 gb sd cards for the DMR? I
believe the firmware is updated to allow this, but has anyone had
experience?

> The major and meaningful size-problem barrier is at 2GB.
> This is because the computer chips inside cameras deal in
> 32-bit chunks of information. The 32 bits hold numbers in binary,
> and each binary bit doubles the size of the number that it can
> hold. 1,2,4,8,16,32,64,128,256,512, and so forth.
>
> If you start with a 1 and double it 31 times, you get the number
> 2,147,483,648 which is 2 giga.
>
> 2,147,483,647 is the largest number that you can represent in a
> 32-bit system without special tricks. The reason you can't double
> again to get 4 gig -- 4,294,967,296  -- is that that last bit is
> needed to indicate negative numbers. On a regular 32-bit computer
> if you take the number 2,147,483,647 and add 1 to it, the answer
> will be -2,147,483,648 instead of +2,147,483,648. Bad mojo.
>
> So if you're going to build a digital system that deals with
> /anything/ bigger than 2GB, it needs to be patiently constructed to
> use two 32-bit data items to stand for a single number. This is
> tedious, error-prone, and slow, so deadline-wracked engineers don't
> do it until they have to, and they usually get it wrong the first
> couple of times.
>
> The next size bomb lurking in digital systems is 140 gig, which
> is the limit with a 48-bit system. Most computers built before
> aboutg 2000 or 2001 can't use hard drives bigger than 140 gig.
>
> 64-bit systems can deal with numbers up to 9,223,372,036,854,775,807
> which is higher than I can count and certainly bigger than any
> storage device that's going to be made in my lifetime. So there's
> no need when building digital controllers to use more than two 32-bit
> items to store one number. This means there won't be a repeat of
> the 2GB problem at 4GB or 8GB or 16GB or whatever. If you can deal
> with something bigger than 2GB, then you can deal with pretty much
> anything.
>
>
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