Hard disks are circular magnetic storage devices that store information. They typically spin at 3,600 RPM and have read/write heads that move within 10-25 millionths of an inch across the disk surface. IDE and SATA are common interfaces that connect hard disks to computers. IDE supports up to four devices across two channels while SATA provides faster speeds and hot-swapping. SCSI interfaces provide more consistent transfer speeds independent of the CPU compared to IDE, making them suitable for multimedia or CAD work. Optical disks like CDs and DVDs store information using lasers to read information encoded in pits on the disk surface. Rewritable disks like CD-RWs and DVD-RWs allow erasing and rewriting