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Read Only Memory (ROM)
Information stored in ROM is permanent in nature, that is, 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.
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 compared to primary memory.
Secondary memory devices are also called secondary storage devices. They are categorised
into three types:
Secondary Storage Devices
Magnetic Disk Optical Disc Flash Drive
Hard Disk Solid State CD DVD Blu-ray Disc Pen Drive Memory Card
Drive (SSD)
Magnetic Disk
A circular metallic disk covered with a magnetic coating, that is used for storing data, 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 called platters.
Each disk in the hard disk has top and bottom surfaces on which data
is recorded using a magnetic head. It is permanently fixed in the
computer system. It is usually used for permanent mass storage. The
most important function of the hard disk is to store program files
and data files.
The hard disk comes in a variety of sizes with storage capacities as
high as 12 TB (Terabyte) or even more. The CPU 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 hard disks that will
be connected to any computer with the help of a USB port.
The first commercially available hard disk drive was the IBM 350 Disk File, which
was introduced by IBM in 1956. It had a storage capacity of about 3.75 MB.
Data Storage and Memory 9

