Hard Disc

A hard disk is a data storage device that stores data on rotating magnetic platters. A typical hard disk drive design consists of a central axis or spindle upon which the platters spin at a constant speed. Moving along and between the platters on a common armature are the read-write heads, with one head for each platter face. The armature moves the heads radially across the platters as they spin, allowing each head access to the entirety of the platter.

IDE
Integrated Drive Electronics - the more commonly-used name for the Advanced Technology Attachment interface standard. It was until recently one of the most common interfaces especially in desktop PCs. It is still widely used for CD / CD-R interfaces.
Many terms and synonyms for ATA exist, including abbreviations such as IDE, ATAPI, and UDMA. ATA standards only allow cable lengths up to 18 inches (up to 450 mm) although cables up to 36 inches (900 mm) can be readily purchased, so the technology normally appears as an internal computer storage interface. It provides the most common and the least expensive interface for this application.
For most of ATA's history, ribbon cables had 40 wires, but an 80-wire version appeared with the introduction of the Ultra DMA/66 standard. The 80-wire cable provides one ground wire to each signal wire. This reduces the effects of electromagnetic induction between neighboring wires and enables the a faster data transfer rate..
 Up to 2 drives can be connected to a single interface in eithe a Master / Slave configuration or using Cable Select In this mode of operation, the drives automatically configure themselves as master or slave. This is achieved by cutting wire 28 (on 40 wire cables, or wires 56 and 57 on 80 wire cables) between the two HDD/CDROM connectors. Some newer cables have this done internally in the connectors. In this case, the two connectors are of different colours. The configuration of a drive to either Master, Slave or Cable Select is carried out by moving a jumper at the rear of the drive.