First generation - 1946-1956 - Vacuum tube hardware - bulky and unreliable, generated excessive heat, and were difficult to program.
Second generation - 1957-1992 - Transistors - faster, more reliable, and easier to program and maintain.
Third - 1964-1970 - Integrated circuits, remote data entry, telecommunications - operated on integrated circuits, which enabled computers to be even smaller, faster, more reliable and sophisticated. Remote data entry and telecommunications were introduced in this generation.
Fourth - 1971-1992 - Miniaturization, VLSI, personal computers, optical discs - continued several trends that further improved power and speed of use: miniaturization, very large scale integration (VLSI) circuits, widespread use of personal computers, and optical discs (discs written or encoded and read using a laser optical device.)
Fifth - 1993-present - parallel processing, gallium arsenide chips, optical technologies - include parallel processing (computers containing hundreds or thousands of CPUs for rapid data processing), gallium arsenide chips that run at higher speeds and consume less power than silicon chips, and optical technologies.
(Secondary memory) made of Mylar or metal, and is used for random-access processing. In other words, data can be accessed in any order, regardless of its order on the surface. Magnetic disks are much faster but more expensive than tape devices.
a. Compact disc read-only memory (CD ROM), as the name implies, is a read-only medium. CD-ROMs are easy to duplicate and distribute and are widely used in large permanent databases, such as for libraries, real estate firms, and financial institutions. They are sometimes used for multimedia applications and to distribute software products. However, because of their larger capacity digital versatile disc read-only memory (DVD-ROMs) are used more often now, particularly for software distribution. A write once, read many (WORM) disc is also a permanent device. Information can be recorded once and can't be altered. A major drawback is it cannot be duplicated. Used to store permanent information