Mass storage

In computing, mass storage refers to the storage of large amounts of data in a persisting and machine-readable fashion. Devices and/or systems that have been described as mass storage include tape libraries, RAID systems, hard disk drives, magnetic tape drives, optical disc drives, magneto-optical disc drives, drum memory (historic), floppy disk drives (historic), punched tape (historic) and holographic memory (experimental). Mass storage includes devices with removable and non-removable media. It does not include random access memory (RAM), which is volatile in that it loses its contents after power loss.
The notion of "large" amounts of data is of course highly dependent on the time frame and the market segment, as mass storage device capacity has increased by many orders of magnitude since the beginnings of computer technology in the late 1940s and continues to grow; however, in any time frame, common mass storage devices have tended to be much larger and at the same time much slower than common realizations of the contemporaneous primary storage technology. The term mass storage was used in the PC marketplace for devices far smaller than devices that were not considered mass storage in the mainframe marketplace.
Mass storage devices are characterized by:
Sustainable transfer speed
Seek time
Cost
Capacity
Today, magnetic disks are the predominant storage media in personal computers. Optical discs, however, are almost exclusively used in the large-scale distribution of retail software, music and movies because of the cost and manufacturing efficiency of the molding process used to produce DVD and compact discs and the nearly-universal presence of reader drives in personal computers and consumer appliances. Flash memory (in particular, NAND flash) has an established and growing niche as a replacement for magnetic hard disks in high performance enterprise computing installations because it has no moving parts (making it more robust) and has a much lower latency; as removable storage such as USB sticks, because in lower capacity ranges it can be made smaller and cheaper than hard disks; and on portable devices such as notebook computers and cell phones because of its lower size and weight, better tolerance of physical stress caused by e.g. shaking or dropping, and low power consumption.
The design of computer architectures and operating systems are often dictated by the mass storage and bus technology of their time. Desktop operating systems such as Windows are now so closely tied to the performance characteristics of magnetic disks that it is difficult to deploy them on other media like flash memory without running into space constraints, suffering serious performance problems or breaking applications.