Cylinders versus tracks...

* Jules Richardson wrote: Out of interest, which is the correct terminology when defining a single point on a disk's surface - is it better to talk in terms of cylinders, or tracks? People often seem to talk about floppy drives in terms of tracks, heads and sectors (e.g. for an 80 cylinder floppy with two sides they'll still talk in terms of tracks 1-80 in conjunction with a side number, even though the media has 160 tracks in total) Talking in terms of cylinders seems to be generally the norm with hard disks though, and perhaps seems a bit more sensible - but remember that hard disk manufacturers are the people who introduced decimal megabytes into common use :-) Personally I prefer to talk in terms of 'surface number' rather than 'head number', as a given surface could conceivably have more than one head in order to improve media latency - but I'm unsure as to whether to use cylinder/surface/sector or track/surface/sector. It's all just semantics, but for the stuff I'm currently working on I'd rather go with the 'correct' version even if that happens not to be the one most commonly used... cheers Jules -------------------------------------------------- Tracks was the original terminology when only one surface was used. For example on some of the early single sided floppies. Cylinders were used to describe a head switch to a new surface. The head switch would be very fast (faster than a one track seek) so continuous data could be recorded on the same track on different surfaces - in effect, a cylinder. So tracks is accurate even on multiple surfaces. But cylinders implies that data is written on all available heads before a seek is performed. With the advent of the embedded servo, tracks no longer line up neatly. A head switch may involve the new head seeking 10-100 tracks to get back to the same track number. Current state of the art is ~150K tracks per inch. So even a small difference is a lot of tracks. And 1 track seeks are now very fast, so it is rare to see controllers doing the cylinder concept. Because the usage and language has changed with time, the use of cylinders versus tracks depends a lot on the vintage of drive and controller. Cylinders were the most efficient way to use an SMD era drive with a dedicated servo surface. But they are performance lagging on today's drives. The amount of data on a track is variable and has been for many years. So the drive is divided into zones, which have a different amount of bits per track for each zone. Drives may have as many as 50 zones, ie 50 different numbers of bits per track. Modern drives often have a different number of tracks on each surface. So a single platter drive could have 2 different track counts, one for each surface. Thus current state of the art drives can have a huge difference in the number of tracks and amount of data on the surfaces. For example, a 100GB single platter drive may have 44GB on one surface and 56GB on the other surface. Because of this, you need a decoder program to even find what track you on. Cylinder and tracks don't have much meaning at the interface level. Consequently, we normally use LBA - Logical Block Address - and don't pay much attention to tracks or cylinders. Except when trying to physically view of certain spot on a disk. Billy