HP drives

Except for a ferw very odd ones (e.g. hard drives which record analagoue singals such as analogue video [1]) every hard disk I've worked on has used both sides of all platters for something. Maybe not user data storage (for excample, it may contain servo information only), but there will be a head on it. [1[] Yes such things did exist. They were used for action replays on TV, for exmaple. And somewhere I have a vido output system for the PDP11 which uses a special hard disk as its video memeory). In the context of a hard disk, though, a 'cylinder' means all the tracks that can be accessed without moving the heads. So if you have 4 data surfaces (such as the ST412), a cylinder contains 4 tracks. In an RK07, which has 3 data surfaces and 1 servo surface, as cylinder it 3 tracks. And so on. -tony