Hard disk label vs. actual capacity difference seems excessive...

I just purchased the Western Digital WD6400AAKS drive which is listed/sold as a 640GB hard drive. I installed it, then when in the Windows setup part where you create the partition, its shows a value of 618,xxx,xxxMB. Now in the past I've seen the number showing much lower that what appears in Windows so I thought it was a little strange but then remembered that much. Then, when I start Windows, when I right click the drive to format it, the formatting window shows 596GB I know in the past that the advertised/labeled capacity is slightly higher than what you actually get, but a loss of 40+GB?? That seems a bit excessive... This is the largest drive I have had yet since installing my '80GB' which broke down to 74.5GB total in Windows (XP), and I thought that was bad. Is this normal with drives this large? With ANY drives? Is there a way to maximize capacity? This could make a difference in my future plans

Yep, after formating a 1TB drive actually turns out to be 931MB.

The file system (format of the hard drive; NTFS, Fat32) itself takes up space too.

Yeah, so it would be 931 gigabytes, but only .904 terabytes....

Whatever, it's weird.

It's actually pretty simple stuff. Computers use a binary number system! Basically everything is 2 to the power of some number:
2, 4, 8, 16, 32, 64, 128, 256, 512 1024, 2048... and so on. If you look through that list you'll notice a few common computer numbers. (e.g. 512 mb of ram, ever wondered why its 512 not 500? or why 2Gb of ram is actually 2048 megabytes?).

So basically there are 1024 bytes in a kilobyte, 1024 kilobytes in a megabyte and 1024 megabytes in a gigabyte. So 500 gigabytes is actually 500 x 1024 megabytes which equals 512000 megabytes or 512000 x 1024 kilobytes which equals 524288000 kilobytes.

Now in the normal decimal system kilo means 1000, mega means a million etc.
So what the manufacturers sell is 640 gigabytes using the "decimal" giga, not the "binary" giga:

640 x 1000 = 640 000 "megabytes"
640000 x 1000 = 640 000 000 "kilobytes"
640 000 000 x 1000 = 640 000 000 000 "bytes"

BUT the computer reads this number in binary! So 640 000 000 000 bytes divided by 1024 = 625 000 000 kilobytes, not 640 000 000!
625 000 000 divided by 1024 = 610 351.56 megabytes
610 351.5625 divided by 1024 = 596.04 gigabytes.

So there you go! To summarize, when selling they use decimal, but the computer uses binary.

I guess you're right, it isn't the hard drive manufacturers at all, it's actually windows. Because there really are technically 640 billion bytes, or 640 gigabytes. So yeah... it's just that windows doesn't tell you the correct units.

Be aware that you are not losing space. The confusion happens only if you try to mix different measurement tools. Draw the analogy of measuring a board with a ruler marked off in inches, then again in centimeters. You get VERY different numbers. If you cut the board into 4 pieces and measured each with a ruler, then added them up, it would come out OK as long as you use ONLY the inch ruler, or only the cm one, but never mix them.

HDD makers define "GB" or "Gigabyte" as 1,000,000,000 bytes. Microsoft (in Windows) defines it as 1,024 x 1,024 x 1,024 bytes, or 1,073,741,824 bytes. A "Megabyte" is 1,048,576 bytes, and it takes 1,024 of them to make a Gigabyte. As long as you stick with Windows' measurement system, the file sizes and disk capacity numbers all use the same definition. The root of the problem is that two groups are using the same term, "Gigabyte", for slightly different units, unlike the "Inch" vs "Centimeter" situation where it is clearer.

Make the tranlation once at the start. 640,000,000,000 bytes, measured in Windows' units, is 596.046 "Gigabytes" with NONE of it missing. From then on, think in Windows' definitions of the terms and it's all good.

Chookman, it's not that bad. Each of your "500 GB" drives, as measured by the Windows definitions, is actually called 465.67 GB (if you willl agree to call one GB 1024 x 1024 x 1024 bytes). That's with NO space lost, just re-labelled using a new mearuement unit. So the 7 of them would have 3.2596 TB in Windows' units, and you actually have 3.18. You've got 0.08 TB or 80 GB of "lost" overhead on the drives, not 320GB.

Yeah, I kinda figured anyone who set up that kind of storage system knows what they're doing.

Know I'm bringing this back to life. But did I get majorly screwed on my 640gig HD. I formatted mine and after using it awhile never really looked at the actual space but when I did it says complete total usage is 514 gigabytes not 596 everyone is saying it should be. Oh yeah just got this also.. maybe barely a months worth

Some times there's an issue with hidden files. Even on a data-only disk, the Recycle Bin uses space. So if you add up all the files sizes you get a number. Subtract that from the Total Space on the drive and you will find it predicts the Free Space to be bigger than it is. But look closely at Used Space and you'll see it is bigger than the total of file sizes, because the Used Space includes any hidden files (like the stuff being saved n the Recycle Bin). Emptying the Recycle Bin will reduce the Used Space, but there may still be a small discrepancy for other types of hidden files.