The most popular device to store data from a personal computer. Hard disks have been used to store on personal computers for a long time and are now more reliable, fast and can store more data (60gb upwards). Hard disks are stored within the case of a PC and most cases and motherboards allow the ability to store and use 2 hard disks. It is always a good idea to buy a new hard disk when upgrading a CPU or processor, because a CPU can only process data as fast as the hard disk can supply it.