By ghz do you mean GB?
I do know that sometimes when companies say 80 gigabytes, they really mean 80 billion bytes and since there is 1024 bytes in a gigabyte it makes a difference. However, that only accounts for 10 missing gigabytes... weird.
What kind of hard drive is it? Do you have a link we can look at?
AMD Athlon 64 3000+ socket 939 @ 2.3 GHz
MSI K8N Neo2 Platinum motherboard
EVGA GeForce 6800 GT
2 GB DDR 400 (PC 3200) (2 x 1 GB sticks) (Dual Channel)
DVD player and seperate DVD RW drive
80 GB Western Digital Hard Drive
500 watt power supply
Sound Blaster Audigy
Logitech 5.1 surround sound speakers
SAMSUNG SyncMaster 710T LCD monitor
Aspire X Navigator Case