Magnetic tapes and Magnetic Disk:

Magnetic tapes are very commonly used for storing large quantum of data for which rapid access is not necessary; specially for archival data backups etc. Tapes are cheap means of storing data but access is generally slow. Small cassette tapes, of relatively low capacity are used with microcomputers. 

Magnetic Disks are most widely used form of backing storage, suitable for holding information required rapidly for example, data for a running program. In the type of disk drive in larger computer systems, data is recorded on the flat surfaces of a stack of circular disks revolving on a common spindle, with one read/write head for each disk. Access times, typically 0.01  seconds, although much faster than tape, are rather slow, by comparison with other computer operations, and disk access times are one of the main limiting factors in the speed of operation of retrieval systems with information stored on disk. 

Disk capacities have increased greatly, from original values of about 10 MB (Mega Bytes to present units with 1 GB (Gigabytes which is one thousand million bytes). Smaller computer systems use Winchester disks, with a single hard disk in a sealed unit, floppy disks, which are compact, cheap and convenient for transfer of programs and data. They are limited in storage capacity, with relatively slow access times, and less convenient than a hard disk in day to day use. Floppy disks now are available in two sizes, 5.25 and 3.5 inches.,