Hard Disk Space

I know that computers reserve space for back-up, sys storage, etc etc. But my computer does not show 640 GB as it was advertised. It only shows 584 GB HD space, 11.08 in recovery partition, and 100 MB reserved (from computer management). All add up to around 610 GB. It may as well hide a few other GB for system and memory management. So my basic question would be, how would I know in a Sony VPCEG37FM/ White (that advertised the HD as 640 GB), how the HD space has been divided up?

Try WinDirStat: http://windirstat.info/
...but know that HDDs are slightly upsold by their manufacturers. Hard drive makers and the Windows OS use slightly different definitions of gigabytes. From the Wikipedia "Gigabyte" page: "Since the early 2000s most consumer hard drive capacities are grouped in certain size classes measured in gigabytes. The exact capacity of a given drive is usually some number above or below the class designation. Although most manufacturers of hard disk drives and flash-memory disk devices define 1 gigabyte as 1000000000bytes, software like Microsoft Windows reports size in gigabytes by dividing the total capacity in bytes by 1073741824, while still reporting the result with the symbol "GB". This practice is a cause of confusion, as a hard disk with a manufacturer-rated capacity of 400 gigabytes might be reported by the operating system as only "372 GB", for instance."

Both are right actually since a hardware GB means Gigabyte, while an OS GB means Gibibyte. HDD makers use Gigabyte since it looks cleaner and it makes their numbers bigger, while software tends to work in base 2 and use Gibibytes.