Data storage is one of the most important functions of any computer system. Devices that are used to store information use different technologies which allow them to store information for a certain period of time and in a certain manner that decides its accessibility and usability.
Computer data storage devices store information in digital forms. They are classified into different types according to their unique characteristics. The three basic types of data storage devices are primary storage, secondary storage, and tertiary storage.
Basically, primary storage is the memory part of the computer. It includes the Random Access Memory (RAM) and Read Only Memory (ROM).
Random Access Memory (RAM)
Random access memory is used as a scratch pad by the computer's processor to store information temporarily. The random access memory is a volatile memory that loses information as soon as you turn off the computer. However, its access rate, which is the time required by to access the stored data, is greater than that of the read only type of memory. Also, RAMs are a bit more expensive than the read only memory.
Read Only Memory
Read only memory (ROM) is a type of storage that is used to store information permanently. Data is stored in this type of memory either at the time of manufacturing, or is added later by the user. The data entered into a ROM cannot be changed once written (non-volatile). The access rate of this type of primary storage is less than that of the RAM. Lastly, ROMs are not as expensive as RAMs.
Hard disks, magnetic tapes (now obsolete), and all the other storage devices are included in secondary storage. They are external to the processor, and are used to increase the storage capacity of the computer.
Secondary storage is non-volatile, and can retain information even after the computer is switched off. Following are the devices that fall under this category.
Hard disk drives are non-volatile, and in them, data is stored in a digital form on the platters that have a magnetic surface. Earlier, hard disk drives were used as a removable mass storage device. However, nowadays, they come as a completely sealed unit inside the CPU. Portable hard disk drives are also available for expanding the storage capacity of the computer.
Secondary storage also includes offline storage devices, which are those devices in which information is stored, and then they can be disconnected from the computer. They include CDs and DVDs. The main objective of storing data offline is to increase the security of the information, besides using up less space in the computer itself, and also for creating a backup of the data.
CDs were initially used only to record audio files, but today, with technological improvements and the development of different encoding and decoding formats, they are used to store all types of information, including video, audio, as well as other forms of data. Compact discs (CD) are used to store information over a long period of time using optical encoding. They are non-volatile memory devices.
Digital Versatile Disc (DVD)
DVDs store data in the same manner as that of CDs. However, DVDs have a greater storage capacity than CDs. Typically, a DVD has a storage capacity which is six times greater than that of a CD.
Blu-ray discs are often used by video game manufacturers for distributing games, and also for high-definition video storage. The physical dimensions of the blu-ray discs are similar to that of CDs and DVDs, however, their storage capacity is much larger in comparison.
Flash memory is a further advancement in the read only memory segment, with the difference that the information in the flash memory can be electrically erased within seconds. Also, the data can be added to and removed from the flash memory multiple times as per the user's requirements.
Tertiary storage is the third type of data storage. It includes the devices that are connected to the computer in the form of removable mass storage. These are often used to store those files that are rarely accessed by the user.
USB Flash Drives
USB flash drives are connected to the computer via the USB port, and use the Universal Serial Bus (USB) interface for storing and accessing information. They are re-writable and have in-built flash-type memory within them.