Confirming all of the above...there was even a class-action lawsuit against HD manufacturers for using a different measurement of "MB" than everyone else did. It stems from the use of metric/SI prefixes like "kilo-", "mega-", etc, which are meant to be powers of 10 (i.e. kilo- means 10^3), vs. a computer's closest equivalent, which was in powers of 2 (where kilo- was 2^10, or 1024). As disks got bigger, the "error" difference was far more noticeable.
In 2000, the IEC proposed a new set of prefixes which are based on 2^10, like "kibi-", "mebi-" and "gibi-", but they've been widely "accepted" but still little used.
When an OS tells you how big a "disk" is, there are a couple factors:
- Formatted vs. unformatted: A "formatted" disk (remember formatting floppies?!) simply means that the structures used for storing information for individual files, directory/folder structures, etc. hav already been created, and they take space themselves. A formatted disk has already used some space - but depending on the OS and the format (NTFS, FAT, etc.) it will tell you its using little if any space. You'll see that the the formatted capacity is less than the "raw" or advertised unformatted capacity. And the different filesystem formats available make a difference.
- A partition vs. a physical disk. As mentioned, a disk can be partitioned - that is, divided into several logical units that the OS sees as separate physical disks. If we are talking windows, you may see these as addition drives along with C:, like D:, E:, etc., along with your CD/DVD drive which is usually the last of the letters in sequence. However, this is only of they are formatted in a way the OS recognizes.
Some vendors provide a "maintenance" or "recovery" partition.They are usually relatively small compared to the whole disk. 32GB is the largest I remember offhand. My Dell Vista box has 10GB. This contains a copy of the OS that was originally installed, and if I boot a certain way, the OS will be completely reinstalled just as if it was new. Of course, I hopefully have a really good backup of my important data...(note to self, run backup after posting...
). I actually see this as my D: drive.
I also have a "hidden" partition, which contains the program that gets run to rebuild the system, but its only 55MB.
Here is how you can see it in Windows, although it can be different on different versions. Find "Administrative Tools", then go to Computer Management > Storage > Disk Management. You should see a Disk 0, and some blocks that represent the different partitions. Add those up, and that's the size of the disk according to the OS. Mine is a "320GB" drive, but I get 298GB of raw storage. Windows generally reports about the same from the OS point of view as well.
