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Read-only Memory (ROM)
Information stored in ROM is permanent in nature, i.e., it holds the data
even if the system is switched off. It holds the starting instructions that
are required to start a computer. It is also called non-volatile memory.
ROM
Secondary Memory
This memory is permanent in nature and is not directly accessed by the CPU. It allows users to
store data that may be easily retrieved. It is cheaper as compared to primary memory.
Secondary memory devices are also called secondary storage devices. They are categorised into
three types: Magnetic disk, Optical disc and Flash drive.
Secondary Memory
Magnetic Disk Optical Disc Flash Drive
Hard Disk CD DVD Blu-ray Disc Pen Drive Memory Card
Magnetic Disk
A device, covered with a magnetic coating is called a magnetic disk. You can record and erase
data on a magnetic disk any number of times.
Hard Disk
The hard disk consists of one or more magnetic disks. Each disk in
the pack has top and bottom surfaces on which data is recorded
using magnetic head. It is permanently fixed in the system unit.
The most important function of the hard disk is to store program
files and data files. Hard disk
Hard disks are available in a variety of sizes with storage capacities
as high as 5 TB (TeraByte) or even more. The CPU can accesses data
stored on a hard disk much faster than it can access data on a CD.
External hard disks are also available. They are the hard disks
that can be connected to any computer with the help of a USB port.
External hard disk
Tech Fact
First hard disk was introduced by Seagate in 1979 which could hold 5 MB data.
Computer System Organization - I/O devices, Storage devices 43

