Different types of storage devices are optimal for different situations.
Hard disk – A hard disk is appropriate for the system files such as operating system. It is also the best place to save programs that will be used frequently.
Floppy disk – A floppy should be used when there is a need to transfer data from one place to another. A floppy has a limited storage capacity of 1.44M which must be accounted for when deciding what removable storage to use.
RAM – RAM is used for temporary storage of files. It is where program files are stored after a program is started. It can not be used for programs that will need to be accessed frequently because it is volatile and will disappear once the computer is restarted.
CD ROM – A CD-ROM should be used if there is a need to transfer data from one place to another and the contents will not fit on a floppy. A CD-ROM can hold up to 700M of files. They are sometimes used as backup media for servers and PCs. However, someone must keep in mind that A CD-ROM does have a limited shelf life years.
External Harddrive - External Harddrive are a great solution for backup photos and data. Given the decrease in the price of external harddrives recently (1 TerraByte for under $100) every business and personal computer could benefit from one. Originally external harddrives were through the parallel port and were very slow. SCSI devices offered faster access speeds but the modern USB 2.0 drives are just as fast or faster.
Flash / Thumb Drives - Quite simply flash drives have replaced floppy drives. Most new computers do not contain floppy drives. Flash drives are a lot more durable and have a longer shelf life than floppies. They have also decreased recently (4G for $10) which makes it very convenient for students and business people to transfer files from one computer to another. Flash drives like all memory are acceptable to virus so ensure you have virus detection and latest definitions installed.