Cylinders

A cylinder is a set of matched[24] tracks.
On a double-sided floppy, a track from the top surface and the same # track from the bottom surface of the disk make up a cylinder. The concept is not particularly[25] useful for floppies.
On a hard disk, a cylinder is made of all the tracks of the same # from all the metal disks that make up the "hard disk".  If you put these all together on top of each other, you'd have something that looks like a tin can[26] with no top or bottom - a cylinder.

The computer keeps track of what it has put where on a disk by remembering the addresses of all the sectors used, which would mean remembering some combination of the cylinder, track, and sector. Thank goodness we don't have to remember all these numbers!    Where the difference between addressing methods shows up is in the time it takes for the read/write head to get into the right position. The cylinder method writes data down the disks on the same cylinder. This works faster because each metal platter has a read/write head for each side and they all move together. So for one position of the read/write heads, the computer can put some data on all the platters before having to move the heads to a new position.

What happens when a disk is formatted?

1.	All data is erased. Don't forget this!!
2.	Surfaces are checked for physical and magnetic defects.
3.	A root directory is created to list where things are on the disk.

Disc Capacity

The capacity of a magnetic disk depends on several factors. We always want the highest amount of data stored in the least possible space. (People are so greedy_[27] this way!) So the capacities of storage media keep increasing_[28] while cost_[29] keeps decreasing. It's a lovely situation for the user!

Capacity of a Disk depends on:

1. # of sides used:
single-sided	double-sided
2. Recording density - how close together the bits can be on a track sector of the innermost track
3. # of tracks on the disk

Capacity of Disks

	5ј" floppy	- 360 KB or 1.2 MB
	3Ѕ" floppy	- 720 KB or 1.44 MB
	Hard disk early ones = 20 MB currently (March 2003) = 120+ GB  where 1 GB  = 1 gigabyte = 1024 MB

Future??? Advances in technology for the read/write head and for the densities_[30] on the disks are bringing larger and larger disk capacities for about the same price. In fact, you cannot find a small capacity drive to buy, even if you wanted one! 120 GB drives are plentiful_[31] (March. 2003) and for the same price that we used to buy 1 Gig drives (under $200). It's enough to make you cry to think of what we paid over the years and what we could get for those dollars today. Ah, well. That's the way the computer world works!