Text C: Data Storage Devices

Data storage devices may be used either as a memory or as a secondary storage device. In most cases, storage capacity is measured in bytes, with one byte (B) usually equal to one character.

Primary storage is the memory part of the computer itself. It includes RAM and ROM. Random access memory (RAM) chips are mounted directly on the computer’s main circuit board. RAM is temporary and volatile. It is used to store instructions and data temporarily. Read-only memory (ROM) – is usually nonvolatile. ROM provides permanent storage for data and instructions that do not change, like programs and data from the computer manufacturer. In a PC, the ROM contains a specialized program called the BIOS that controls loading the computer’s operating system from the hard disk drive into RAM whenever the computer is turned on.

The CPU contains a special set of memory cells called registers that perform much more rapidly than the main memory area. Registers are used for the most frequently needed data items.

Cache memory is a type of high-speed memory that a processor can access more rapidly than main memory. A cache controller determines how often the data is used, transfers frequently used data to cache memory, and deletes the data when it goes out of use.

Programs and data that are not currently being used in main storage can be saved on secondary storage. The secondary storage is non-volatile and has greater capacity. Secondary storage devices include: internal and external hard drives, CDs, DVDs, flash memory, USB flash drives, etc. The hard drives are one of the most important of the secondary data storage devices. “Flash drive” is a solid state drive technology that stores data like a typical hard drive found in most PCs, but uses no moving parts. Flash drives come in many forms. For example, a USB flash drive – a very small, very portable storage device which can be plugged into a computer system via a USB port and used immediately. Installing operating system (thin clients) on this device allows one to plug this device in any computer without interfering with any of the data on the host computer.

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