[SOLVED] Why hard drive capacity shows 600GB vs 640GB?

[jaderiver]

Why do my computer directories, both in Linux 13 MATE and Windows 7 OS's (and GParted) indicate only 600GB total space, when my computer actually has 640GB? The computer advertised as 640GB, so when I first explored and saw a total of "600 GB," I thought there was false advertising, but thought, okay, I can live w/ 600 GB (but was sort of peeved.) Then, while installing Mint 13 MATE for a dual boot, I was customizing partitions and saw that a total of 640 GB was definitely showing up during MATE installation procedures. But now, everything adds up to only 600 GB again.

It seems that the 500 GB I allocated for the /home directory is now showing capacity for only 465 GB, which may be part of the problem. And, I am accounting for the WIN 7 hidden 25 GB recovery partition, which shows up in GParted.)

Probably a newbie question, but can somebody tell me what is going on? Are there hidden files unseen? Why is the /home directory so much less than I allocated? Any other information about this issue would be helpful.

My storage capacity should show 640 GB. Other specs: Core i5/Sandy B.64-bit/2430 M; 8G mem; DDR3; 5400 RPM (see signature).

Thank you for your time.
jaderiver

[srs5694]

There are two issues that commonly account for such discrepancies:

• SI vs. IEEE-1541 units -- The international system of units (SI units) specifies prefixes used in the metric system (kilometers, milligrams, etc.). These include kilo (k), mega (M), giga (G), and so on. These units are defined using power-of-10 units -- kilo means 1,000, mega means 1,000,000, and so on. For years, the computer field has misapplied SI units to power-of-2 units, with kilo meaning 1,024 (2^10), mega meaning 1,048,576 (2^20), and so on, since the SI units were "close enough" (an odd attitude in a field where precision is so important). "Close enough" has become increasingly imprecise as disk sizes have increased, though. Thus, the IEEE-1541 standard now defines new prefixes for the power-of-2 units: kibi (Ki) for 1,024, mebi (Mi) for 1,048,576, and so on. If one utility is using SI units and the other is misapplying the SI prefixes to base 2 units, then there will be a discrepancy. There may seem to be a discrepancy if one utility is using SI units and the other is using IEEE-1541 units but you don't recognize the difference. If everybody used the correct units, then you'd at least have a clue in that one would say "MiB" or "GiB" whereas the other would say "MB" or "GB;" but all too often the units are mis-reported. This effect is almost precisely the same as the discrepancy you note -- 1 GiB is 1,073,741,824 bytes, so 600 GiB is about 644 GB; or 640 GB is about 596 GiB.
• Overhead -- Disk partitioning and filesystems impose overhead that reduces the effective capacity of a disk. Thus, you might be able to store less data than you might expect on a disk. In some cases, disk utilities may report the total usable space after these overhead values are considered, which of course reduces the disk's apparent size. In the size range you're describing, though, this effect is likely to be smaller than the effect of SI vs. IEEE-1541 unit confusion.

[jaderiver]

srs5694... Wow...thank you so much for the fast reply and taking time to write a clear, concise explanation for what is happening. From you I received more comprehensive information than expected, and appreciate very much. I learned something new today. Finally I can put to rest the lingering feeling I always felt about being "shortchanged" 40 GB of storage somewhere along the line.

jaderiver