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Home , Computer memory

STORAGE DEVICES

BY ALEXANDRA DJORDJEVIC , E M M A STADDON , R A M O N A GHARZ EDDIN STORAGE DEVICES • A storage device is a piece of equipment on which information can be stored either temporarily or permanently. STORAGE DEVICES

• There are two types of storage devices used with : a primary storage device, such as RAM, and a secondary storage device, like a hard drive. Secondary storage can be removable, internal, or external storage. PRIMARY STORAGE

• RAM (random access memory) is the place in a device where the , application programs and in current use are kept so they can be quickly reached by the device's . • RAM is much faster to read from and write to than other kinds of storage in a computer, such as a , solid- drive or optical drive. • Data remains in RAM as long as the computer is running. When the computer is turned off, RAM loses its data. PRIMARY STORAGE: RAM VS. ROM • ROM is "built-in" computer memory containing data that normally can only be read, not written to. • ROM contains the programming that allows your computer to be "booted up" or regenerated each time you turn it on. • Unlike a computer's random access memory (RAM), the data in ROM is not lost when the computer power is turned off. • The ROM is sustained by a small long-life battery in your computer. TYPES OF ROM

• PROM • EPROM • EEPROM PROM • Programmable read-only memory (PROM) is read-only memory ( ROM ) that can be modified once by a user. • PROM is a way of allowing a user to tailor a microcode program using a special machine called a PROM programmer. • This machine supplies an electrical current to specific cells in the ROM that effectively blows a fuse in them. The process is known as burning the PROM . EPROM • EPROM (Erasable Programmable Read-Only Memory) is programmable read-only memory (programmable ROM) that can be erased and re-used. • Erasure is caused by shining an intense ultraviolet light through a window that is designed into the memory chip. • Although ordinary room lighting does not contain enough ultraviolet light to cause erasure, bright sunlight can cause erasure. For this reason, the window is usually covered with a label when not installed in the computer. EEPROM • EEPROM (electrically erasable programmable read-only memory) is user- modifiable read-only memory (ROM) that can be erased and reprogrammed repeatedly through the application of higher than normal electrical voltage. • Unlike EPROM chips, do not need to be removed from the computer to be modified. However, an EEPROM chip has to be erased and reprogrammed in its entirety, not selectively. • It also has a limited life - that is, the number of times it can be reprogrammed is limited to tens or hundreds of thousands of times. • In an EEPROM that is frequently reprogrammed while the computer is in use, the life of the EEPROM can be an important design consideration. • A special form of EEPROM is , which uses normal PC voltages for erasure and reprogramming. SECONDARY STORAGE

• Secondary storage is used to protect inactive data written from a primary storage array to a non-volatile tier of disk, flash or tape. • Secondary storage is synonymous with the terms secondary memory, auxiliary storage and external storage. • Secondary storage is a trade-off between high performance and economical long-term archiving. Because it is accessed less frequently, data can be migrated to secondary storage devices with lower performance and costs. THE END