320gig hard disk, only 299 shown after installing windows 7 [duplicate]

320gig hard disk, only 299 shown after installing windows 7 [duplicate]

I just purchased a Dell Inspiron 1410 without OS. In the BIOS, it shows 320 GB of hard disk space. After I installed Windows 7 Ultimate, only 299 GB total hard disk space is shown. I only got one partition. I run a partition manager, it shows only 299 GB, without any partition that has the other 20 GB.