Welcome to the wonderful world of slack space. The issue is a numerical "faux pas". What happens is that your hard drive is measured in base-10 numerals, where 1gb=1000mb, 1mb=1000kb, and so on. This means that 82.3gb= 82,300,000,000 bytes.
In actuality, the drive should be measured in base-1024 numerals, where 1gb=1024mb, 1mb=1024kb and so on. This would mean that your 82.3gb drive = 88,368,952,115.2 bytes.
But as you have seen, this is not the case. Your drive is approximately 82.3gb give or take a few mb's. You have "lost" some space simply because of a discrepancy between the marketing world and the real world. Also, you lose some space on the drive when you format.
Base-10 numbering is a holdover from the old days when it was easier to just label a 1gb drive as a "1gb drive". After all, the consumer only "lost" 48mb in the process.
That's not much when you think about it, right? But when you add up all those 48mb chunks across an "82.3gb" drive, you get 5.7gb of actual space that has been "lost".
it is a little confusing to some, but just remember that a drive rated in the base-10 scale will always be smaller than the advertised specs.