Hard Disk Drive

• The HDD installs in one of the 3-1/2 inch internal drive bays in the PC. It is secured by machine screws. 

• It is powered by a 4 conductor cable coming from the power supply. 

• Data to and from the motherboard is carried on a 40-pin IDE (Integrated Drive Electronics) cable. 

• Data is stored magnetically on multiple rigid disks that are stacked up like pancakes. Small arms with magnetic pickups move rapidly back and forth across the top and bottom surface of each disk in the drive. The sensors float just a few microns above the rotating disk surface and can read and write data at very high rates. 

• Most commercially available hard drives rotate at 5400 or 7200 RPM (revolutions per minute) which translates to 90 or 120 revolutions per second respectively. The data transfer rate from the drive to the motherboard is 33 Mbytes/second in bursts. Newer drives are capable of higher speeds up to 66 Mbytes/sec. To use this faster drive, the PC must have an ATA/66 interface that is capable of keeping up with it. 

• A 40 Gbyte HDD sells for about $100.