Approximately 15Gb of that space is your XP OS, so that only leaves about 13Gb for everything else on your PC, which is not a lot!
Your memory is not 80Gb - you hard drive Capacity is 80Gb, memory is something else.
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Synology invites you to visit them at Insomnia on 26th – 29th August. Book your tickets now and visit Synology.