CPU stands for central processing unit. CPU is the brains of the computer. Sometimes referred to simply as the processor or central processor, the CPU is where most calculations take place. In terms of computing power, the CPU is the most important element of a computer system.
Three typical components of a CPU are
- RAM (random-access memory): This is the same as main memory. The term RAM refers to read and write memory; that is, people can both write data into RAM and read data from RAM.
- ROM (read-only memory): Computers almost always contain a small amount of read-only memory that holds instructions for starting up the computer. Unlike RAM, ROM cannot be written to.
- PROM (programmable read-only memory): A PROM is a memory chip on which people can store a program But once the PROM has been used, you cannot wipe it clean and use it to store something else.
- EPROM (erasable programmable read-only memory): An EPROM is a special type of PROM that can be erased by exposing it to ultraviolet light.
Secondary Storage Devices
Refers to various techniques and devices for storing large amounts of date. Modern mass storage devices include all types of disk drives and tape drives. Mass storage is distinct from memory, which refers to temporary storage areas within the computer. Unlike main memory, mass storage devices retain data even when the computer is turned off.
The main types of mass storage are:
Floppy disks: Relatively slow and have a small capacity, but they are portable, inexpensive, and universal.
Hard disks: Very fast and with more capacity than floppy disks, but also more expensive.
Optical disks: Unlike floppy and hard disks, which use electromagnetism to encode data, optical disk systems use a laser to read and write data. Optical disks have very large storage capacity, but they are not as fast as hard disks.
Tapes : Relatively inexpensive and can have very large storage capacities, but they do not permit random access of data.