Floppy disks is a magnetic storage medium, the data being encoded on a disk which is protected by an exterior cover or sleeve. Early covers were soft and flexible (hence floppy) sleeves though later disks were rigid plastic enclosures.
|Some of my floppy disks... or 3-D printed save icons if you prefer|
The 5.25" floppy disk first appeared in the mid-1970s and held sway as the major data storage format for personal computers well into the 1980s. In the mid-1980s the 3.5" floppy disk appeared and this remained the standard disk format until the concept of the disk itself was obsolete in the early 2000s. There were smaller disks formats around such as the 2" floppy used on the the Zenith minisport (a photo of my one below) though these did not find much favour.
Indeed in the case of the Zenith the 2" disks were hard to find (and pretty expensive if you did) so an external 3.5" floppy disk drive tended to be used instead. This reduced the usefulness of the computer as a "portable" of course.
The end of the floppy disk drive as the major removable storage medium came fairly quick. The Apple iMac was released in 1998 and was the first high-profile personal computer from a major manufacturer without a floppy disk drive. Although external drives sold well at first many people (including myself) learned to live without a floppy disk drive. By the 2000s computers were increasingly being sold without the drives. A major reason being the limited capacity of floppy disks and the rise of better alternatives.
The 3.5" floppy drive usually held 720KB or 1.4MB (earlier floppies held less, some could hold as much as 2.8MB). As software grew more complicated and powerful file sizes increased dramatically - floppy disks became an inconvenient as a medium for software installation. Major pieces of software such as OS/2 came on as many as 30 disks (i have read that there was a floppy disk release of Windows XP that came on 250 disks though cannot verify if that is true), even applications like Quattro Pro came on over half a dozen. Installing software, and having to switch disks every few minutes was a pain - especially in a commercial environment. It became much easier to install off a CD-ROM, and later over the network.
Saving your work to floppy became increasingly inconvenient as file sizes increased too. Even a virtually empty Word file can be a few 100KB now. The Photoshop file of this blog's header is 1.1MB, and so would still fit on a high density floppy disk though you would have little space left for anything else! People did transfer files bigger than the capacity of a single floppy as there were ways of getting around this such as using split archives which chopped a file up into "floppy-able" parts which could then be combined on the target machine.
Alternative disk technologies to the floppy disk such as the Iomega Zip (which could typically hold 80MB) became popular in the late 1980s and 90s as did CD-RW burners though no alternative format ever approached the popularity of the basic floppy. Now you would be hard pressed to find a computer with any sort of drive, even CD/DVD drives are becoming rare. The network (that mysterious "cloud") is where all the data appears to be now.