Why don't thumb drive makers compensate for formatting?

They do; look for asterisks and fine print. Some of them simply say that the advertised capacity is without formatting, but some also give the formatted capacity.

As for why they don’t add the extra size, that has to do with addressing. It’s easy to address a 16GB or 32GB drive, but a bit trickier to address a 27GB drive or other weird number, so they make the raw drive an easy-to-address size and then put in fine print formatted capacity is…

Marketing. XKCD elaborates.

Business 101. (Fool the customer) In this case, it’s not that harsh. I agree though, if advertising for 500gb HD. Why not just add the extra amount of memory it takes for storing whatever automatic software there is on the HD.

If it makes you feel better you could count the gigabyte’s in binary instead.

I’m sure the marketing dweebs use the raw capacity because it sounds larger.

But a long time ago, in a galaxy far, far away, it was customary to state the raw capacity rather than the formatted capacity of such things as hard drives because formatted capacity varied depending on the method of formatting, and wasn’t a function of the design of the drive itself. For example, DOS, CP/M, Unix, Mac, etc. all used different formatting methods which yielded different amounts of usable capacity.

@HungryGuy There is that. HFS != FAT12, so a 1000KB raw disk would get you 720kb on a DOS-based PC or 800kb on a Mac. In that case, what is the capacity of the disk?

@jerv – The raw capacity of any mechanical drive is the number of cylinders, times the number of tracks per cylinder, times the number of bits per track. But if you want to be able to separate that space into chunks to store files, you have to “format” it into sectors. The more sectors per track, the more space is wasted in overhead. But if you use large sectors, even tiny files need at least one sector and waste that space.

Think of it in terms of real estate. Your unformatted drive is an open unimproved field…

You can build a gazillion cookie cutter development homes. A lot of space will be wasted on roads, but you can house a gazillion people.

Or you can build a few dozen McMansions. Less wasted space on roads, and your “formatted capacity” will be higher, but in most cases you’ll end up with one or two people per McMansion, so your utilization will be pretty poor. So even though your total capacity is higher this way, it’s inefficient.

@HungryGuy .Yes, block size matters, which is why you don’t want to use 64kb blocks if most of your files are 1—2kb text files; each file will take up a whole block, so some files may take up 50 times more space than they need to.