I just purchased a Samsung Galaxy S3 32GB, when I check the storage I have only 25.5GB. Where is the other 6.5GB?
Usually this space is taken up by various things that come with the device, like resources for the OS, built-in apps, and just disk information. Even formatting an 8 GB SD card will only get you 7.49 GB. That same logic would leave you with 30 GB, the rest is most likely the OS, and various system resources.
The 32GB are in 1000Byte = 1KB Logic, and the 25GB should be in Binary Logic, so 1024Byte = 1KB. which gives at first a "loss" of about 2GB: 32GB = 29,8023GiB
the rest of the space is mostly the android system, reserved space for cache etc... one small part will be the journal of the ext file sytstem which is used instead of yaffs. So arround 200-400MB i think will be covered by the ext journal.
you have the same problem with harddisks too. The firms write it in decimal logic but the operating system does it in binary. Some Operating Systems nowadays also write the correct GiB or MiB or KiB but not all...