External Storage Devices

A storage unit is a component of a computer system that stores the data and instructions that will be processed. A storage device is a component of computer hardware that stores data and information to process the results of computing work. A computer would not be able to run or even load up without a storage device. A storage device is a piece of hardware that is used to store, transfer, or extract data files. It can also temporarily and permanently store data and information. There are two classes of computer storage:

  • Primary Storage Devices: Internal memory and main memory are other names for it. The program instructions, input data, and intermediate results are all stored in this portion of the CPU. It is usually a smaller size. Primary storage includes RAM (Random Access Memory) and ROM (Read Only Memory).
  • Secondary Storage Devices: Secondary storage refers to memory that is kept outside of the computer. It is mostly used for the long-term and permanent storage of programs and data. Secondary storage includes hard discs, CDs, DVDs, Pen/Flash drives, SSDs, and other devices.

Storage Devices

There are different types of storage devices available in the market.

3. Primary storage devices

(i) RAM: R.A.M. is an acronym for Random Access Memory. It is used to store information that will be used right away, or it may call it a transient memory. Computers load software from a hard disc into RAM so that it can be processed and used by the user. The data is destroyed after the machine is switched off. Computers can do various tasks with the use of RAM, such as loading software, browsing the web, creating a spreadsheet, playing the latest game, and so on. It enables users to swiftly move between these jobs while remembering where users were in the previous one. It’s also used to load and run programs, such as the spreadsheet program, and to respond to commands. There are different types of RAM.


SRAM: It stands for Static Random Access Memory. It is made up of circuits that store data as long as the power source is turned on. Volatile memory is another name for it. It is employed in the construction of cache memory. SRAM has a faster access time and is significantly faster than DRAM, however it is more expensive than DRAM in terms of cost.

DRAM: DRAM is the abbreviation for dynamic random access memory. It is a method of storing binary bits in the form of electrical charges applied to capacitors. DRAM has a slower access time than SRAM, but it is less expensive and has a higher packing density.

SDRAM: (SDRAM) is a type of synchronous dynamic random access memory. It exceeds DRAM. It is commonly utilized in computers and other electronic devices. Following the launch of SDRAM, the industry saw the introduction of improved versions of double data rate RAM, such as DDR1, DDR2, DDR3, and DDR4, which are now commonly utilized in-home/office desktops and laptops.

(ii) ROM: It stands for Read-Only Memory. The data written or saved in these devices is non-volatile, which means it cannot be changed or removed once it is in the memory. It is the memory from which you can only read but not write. This is a non-volatile form of memory. The data is only saved once during the manufacturing process. The instructions for starting a computer are stored in the ROM. The operation is known as bootstrapping. Other electrical appliances, such as washers and microwaves, utilize it as well. Only a few megabytes (MB) of data may be stored on ROM chips, which range from 4 to 8 MB per ROM chip. ROMs are divided into two categories:

PROM: The acronym PROM stands for Programmable Read-Only Memory. The program is centered on the PROM by a special PROM programmer. The information on the PROM cannot be changed once it is been programmed. Because PROM is non-volatile, data is not lost when the power is turned off.

EPROM: It stands for Erasable Programmable Read-Only Memory. It is possible to erase information previously recorded on an EPROM and replace it with new data.

2. Magnetic Storage Devices

(i) Floppy Disk: It is commonly used to store data externally on a personal computer. A Floppy disc is a plastic cartridge that is protected by a protective cover. Floppy discs are being phased out in favor of more modern and efficient storage systems such as USB.

floppy disk

(ii) Hard Disk: It is a hard disc drive (HDD) that uses magnetic storage to store and retrieve data. It is a non-volatile storage device that can be changed or deleted an unlimited number of times. HDDs are used as the secondary storage device in the majority of PCs and laptops. It is essentially a stack of discs, similar to phonograph records. Data is recorded electromagnetically in concentric circles or tracks on every hard disc, and the information is read using a head similar to a phonograph arm (but fixed in a location) to read the information present on the track. The read-write speed of HDDs is not particularly quick, but it is enough.

Hard Disk

(iii) Magnetic Card: It is a card that stores data by changing or rearranging the magnetism of microscopic iron-based magnetic particles on the card’s band. A swipe card is another name for it. It can be used as a passcode (to enter a residence or hotel room), credit card, or identity card, among other things.

Debit card

(iv) Tape Cassette: It is also known as music tape. It is a rectangular flat container that holds data on an analog magnetic tape. It is most commonly used to save audio recordings.


(v) Super Disk: It is also known as the LS-240 or LS-120. It was developed by Imation Corporation and is widely used by OEM PCs. It has a storage capacity of up to 240 MB.

3. Flash memory Devices

It is a less expensive and more portable storage device. It is the most widely used storage device because it is more reliable and efficient than other storage systems. The following are some of the most regularly used flash memory devices:

(i) Pen Drive: It is also known as a USB flash drive because it has flash memory and a USB interface built-in. These devices can be immediately connected to our computers and laptops, allowing us to read and write data into them much more quickly and efficiently. These gadgets are extremely portable. In general, it runs from 1GB to 256GB.

pen drive

(ii) SSD: It stands for Solid State Drive, a type of mass storage technology similar to hard disc drives. It is more durable than hard drives because it does not contain optical discs. It uses less power than hard drives, is lighter, and has a read and write performance that is 10 times faster than hard discs. However, these are also costly. While SSDs perform the same functions as hard discs, their internal components differ significantly. SSDs, unlike hard drives, have no moving parts, which is why they’re called solid-state drives. SSDs use non-volatile storage instead of magnetic discs for data storage.

portable hard disk

(iii) SD Card: It is commonly used to store larger data on electronic devices such as phones, digital cameras, and so on. It is tiny and portable, and the SD card is small enough to fit into most modern gadgets. It comes in a variety of sizes, including 2GB, 4GB, and 8GB.

memory card

(iv) Memory Card: It is commonly found in digital cameras, printers, game consoles, and other electronic devices. It can also be used to store large amounts of data and comes in a variety of sizes. A memory card reader is required to use a memory card on a computer.

(v) Multimedia Card: It is an integrated circuit that’s commonly found in vehicle radios, digital cameras, and other electronic devices. It is a data/information storage device that is external.

4. Optical Storage Devices

Optical Storage Devices are another type of supplementary storage. It is a storage device that can be removed. Here are some examples of optical storage devices:

(i) CD: It has data-storage tracks and sectors on its surface. It has a circular shape and is made of polycarbonate plastic. A CD may hold up to 700MB of data. There are two types:

compact disk
  • CD-R: It stands for Compact Disc read-only. In this type, once the data is written cannot be erased. It is read-only.
  • CD-RW: It stands for Compact Disc read Write. In this type, you can easily write or erase data multiple times.

(ii) DVD: DVDs are data storage discs that are circular and flat. It is available in two distinct sizes: 4.7GB single-layer discs and 8.5GB double-layer discs. DVDs resemble CDs in appearance, however, they have a larger storage capacity than CDs. There are two types:

  • DVD-R: It stands for Digital Versatile Disc read-only. In this type, once the data is written cannot be erased.
  • DVD-RW: It stands for Digital Versatile Disc read Write. In this type, you can easily write or erase data multiple times.

(iii) Blu-ray Disc: It is similar to CDs and DVDs, but it has a storage capacity of up to 25GB. A Blu-ray reader is required to play a Blu-ray disc. This Blu-ray technology reads a disc using a blue-violet laser, which allows for a higher density of information to be stored with a longer wavelength.

5. Cloud and Virtual Storage

Virtual or cloud storage systems have replaced secondary memory in recent years. We can keep our files and other items on the cloud for as long as we pay for cloud storage. Many corporations, primarily Google, Amazon, Microsoft, and others, offer cloud services. We can pay rent for the quantity of space we require and reap numerous benefits as a result. Even though it is kept in a physical device in the service provider’s data centers, the user has no interaction with the physical equipment or its upkeep.

External storage vs. internal storage

Volatile internal storage, often known as primary storage, maintains data that is regularly accessed by a computer’s processor and applications. Nonvolatile external storage is typically slower and less expensive. Because you do not have to physically open up a computer to expand capacity or replace a drive, external storage is usually considerably easier to add and support than internal storage.

Not all active or primary storage is internal, and not all external or secondary storage — such as the cloud or a storage array — is physically connected to a computer. In a stratified storage infrastructure, for example, primary storage could include transactional or mission-critical application data housed on HDDs and SSDs on a centralized NAS or SAN with excellent performance.

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