Modern disk drives are fabulously fast. Seagate announced a new disk drive in the fall of 1997 that spins at 10,000 rpm and can transfer 11 megabytes in one second. However, disks are still much slower than RAM and here's why. First, the actual data transfer rate, the speed at which bits are written onto the platter surface or read from it by the read/write head, depends upon the angular speed of the platter, i.e. its rate of rotation. Since it takes more and more energy to whirl the platters faster, there are practical limits. Moreover, the bearings which anchor the platters to the disk drive frame wear out if it spins too fast.