You format your new 500 GB hard drive and it comes up 465 GB – 7% less – where did the extra space go? Strange as it seems, you’re not missing any bytes on your drive, it’s a difference of opinion on what a Gigabyte means. First, some background, and then we’ll get to your ‘missing’ bytes.
Humans count by decimals: 10^3 = 1000 KB, or one Kilobyte.
1 Gigabyte = 10^9 = 1,000,000,000 bytes
(1 GB = 1000 MB and 1 MB = 1000 KB and 1 KB = 1000 bytes)
Computers count by binary GB: since 2^10 is 1024, 1024 was used as a ‘close enough’ binary equivalent to 1000 and it 1024 was called a Kilobyte
1 Gigabyte = 2^30 = 1,073,741,824 bytes
(1 GB = 1024 MB and 1 MB = 1024 KB and 1 KB = 1024 bytes)
So the use of the word “gigabyte” is ambiguous: the value depends on the context. When referring to RAM sizes and file sizes, it traditionally has a binary definition, 1024 MB but for general purposes, a Gigabyte it means exactly 1000^3 bytes, since the prefix “giga-” refers to 1000 “megas”.
(In order to address this confusion, the International Electrotechnical Commission (IEC) promotes the use of the term “Gibibyte” or “GiB” for the binary GB, however that has not caught on).
Back to your new drive that was advertised as being 500 GB – when you format it and look at it in your operating system, it says it has 465 GB – don’t panic, they both mean the same thing. 500 GB in decimal is 500,000,000,000 bytes, and that’s what you have. (Of course, the marketing department of the hard drive company makes the easy choice to call it a 500 GB (decimal) hard drive).
When your operating system looks at it, it counts by binary, so it counts up 500,000,000,000 bytes and calls it 465.6613 GB (binary)
(465.6613 x 1024 x 1024 x 1024 = 500,000,013,628 bytes)
So you have not lost anything, the same 500 billion bytes are there, just reported in binary GB. Your general rule is that binary GB will report a number 7% less than decimal GB.