Archived posting to the Leica Users Group, 2006/10/10
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Brian, Thanks for the great explanation of the binary milestones. I recall encountering the hard drive limit some years ago. Jim Nichols Tullahoma, TN USA ----- Original Message ----- From: "Brian Reid" <reid@mejac.palo-alto.ca.us> To: "Leica Users Group" <lug@leica-users.org> Sent: Monday, October 09, 2006 11:45 PM Subject: Re: [Leica] Digital questions . . . . > 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. > > > _______________________________________________ > Leica Users Group. > See http://leica-users.org/mailman/listinfo/lug for more information >