There are basically two popular sizes of floppy drives. (however, I consider there have been at least 4 types.):
Type 1 = 5 1/4 inch Floppies. They are almost never used anymore. They are low capacity, and slow; however, they look like this:
Originally, 5 1/4 Inch floppies had 1 side and 185 KB space, they later were formatted at 360KB, and even later, you could format for 720 KB.
Type 2 = 3.5 inch Floppies. These are still very popular; however, they are taking a back seat to CD-ROM for software distribution from most vendors.
These floppies could be formatted at 720 KB (DD2S), 1.2 MB, and 1.44 MB. In some instances, they have been specially formatted at 1.68 MB and 1.72 MB; however, without special software you cannot format at these levels.
These 3.5 inch floppies are excellent for small file portability; however, today, many graphics images alone are larger than the 1.44MB. If you need to carry many large files, they require multiple floppies which become cumbersome to handle.
Notice the disk case is hard, but inside the case, there is a flexible disk called a "platter" or a surface. There are normally two surface on a single platter in a floppy drive. The Read/Write head is on the robot arm that extends over the surface.
The platter on a floppy diskette drive are coated with some magnetic film material that can record data in the form of magnetized spots on the surface. The disk surface has "tracks" that are concentric circles (complete circles) that are next to each other on each surface. The tracks on the outside are larger than the tracks on the inner part of the surface. There may be 200 or more tracks per surface.
Then each surface is subdivided into "sectors".
Each sector on each surface will be able to contain a specific amount of
bytes (8 bit characters), usually 512 bytes per sector. The size of the
sector determines the amount of data that can be written, and the amount
that will be wasted if only a few characters are in a record. A one byte
record written to a sector occupies the entire track in that sector.
A floppy diskette must have a record that defines the disk to the CPU for access/writing. In a DOS environment, this record is the File Allocation Table (FAT). The speed of rotation is a factor in the access speed of the drive. The read/write head must move to the proper track before it can read. Once at the proper track, it must wait for the proper sector to rotate under the head to read the data. This is called the "latency" time.
The more files you have on a diskette, the larger the FAT table. Consequently, if you have a large number of files on the floppy, the less actual data you can put on the drive, for example, with one file on a floppy, you can put almost 1.44MB of data; for 250 files, you might only be able to put 1.2 MB of data on the same diskette!