The secondary storage devices that are either incorporated into the computer or linked to the computer are referred to as the computer’s secondary memory or secondary storage devices. It is also referred to as external memory or supplementary storage in some circles.
Input/output operations are used to access the secondary memory in an indirect manner. It is non-volatile, which means that it retains the data even if the computer is switched off, or until the data is overwritten or removed by another piece of data. The secondary memory cannot be accessed directly by the CPU. The data from secondary memory must first be moved to primary memory before the CPU can make use of it.
A few of the secondary memory or storage devices are explained in further detail below:
1) Hard Disk Drive (HDD):
It is a data storage device that is made of a hard magnetic disc. It is housed within a drive unit and serves as a permanent data storage device.
The hard disc is also referred to as a hard drive in some circles. Due to the fact that it is a non-volatile storage technology, it is a hard magnetic disc that keeps data forever. In a computer, the hard disc is housed within a drive unit on the motherboard, and it is made up of one or more platters that are packed tightly inside an air-sealed shell. Platters are written with data by rotating a magnetic head over them while they are spinning, and the data is stored on them. On a computer’s hard drive, the data stored in general comprises the operating system, installed software, and the user’s files and applications, which may contain photographs and other digital media, movies, audio files, and text documents, among other things.
Components of Hard Drive:
Head actuators, read/write actuator arms, read/write heads, platters, and spindles are the primary components of a hard disc. Towards the rear of a hard drive, there is a circuit board known as the disc controller or interface board, which performs many functions. It is responsible for allowing the hard disc to connect with the computer system.
2) Solid-state Drive:
In addition to being a nonvolatile storage medium, SSDs (Solid State Drives) are also utilised to store and access data. Unlike a hard drive, it does not have any moving parts, and as a result, it has several advantages over SSDs, including quicker access times, noiseless operation, lower power consumption, and other benefits.
As the cost of solid-state drives (SSDs) has decreased, they have become an increasingly attractive alternative to traditional hard drives in desktop and laptop computers. It is also appropriate for laptops and tablets that do not require a large amount of storage.
3) Pen drive:
A pen drive is a supplementary storage device that is small and portable. A USB flash drive, thumb drive, or jump drive are all names for the same device. It communicates with a computer using a USB port. Generally speaking, it is used to store and transport data between computers.
Using a computer, for example, you might prepare a report and then copy or transfer it to a pen drive for later use. Later on, you will be able to connect this pen drive to a computer in order to see and update your report. You may also use the pen drive to store essential papers and images, as well as music and films, which you should keep in a safe location.
Pen drives do not have any moving components; instead, they are made up of an integrated circuit memory chip that saves the information. In this case, the chip is contained within a plastic or aluminium housing. The data storage capacity of a pen drive typically ranges from 2 GB to 128 GB, depending on the model. Furthermore, it is a plug-and-play device, which means that it does not require any extra discs, software, or hardware to be operational.
4) SD Card (Secure Digital):
Secure Digital Card (SD Card) is an abbreviation for Secure Digital Card. Most portable and mobile electronics, such as cellphones and digital cameras, make extensive use of this technology. Using a computer equipped with a card reader, you may remove it from your device and see the information saved on it.
There are several memory chips in the SD card that hold the data; there are no moving elements in the SD card at all. The speed, physical size, and capacity of SD cards are not all created equal, and they may differ from one another in these respects. SD cards come in a variety of sizes, including normal SD cards, mini SD cards, and micro SD cards.
5) Compact Disk (CD):
It is a portable secondary storage device that is shaped like a medium disc and may be carried about. Polycarbonate plastic is used to construct it. Philips and Sony collaborated on the development of the compact disc (CD) idea in 1982. The world’s first compact disc (CD) was made on August 17, 1982, in a Philips workshop in Germany.
CDs were originally used for storing and playing music recordings, but they have since been used for a variety of other applications, including storing documents, audio files, films, and other data such as software programmes on a computer hard drive.
Physical features of a compact disc/structure of a compact disc:
A conventional CD has a diameter of around 5 inches and a thickness of 0.05 inches. It is constructed of a transparent polycarbonate plastic base, a reflective metallic layer, and an acrylic plastic covering that is clear on the outside. Each of these tiny circular layers is bonded to the next one on top of the other in the following manner:
● The data is encoded in a polycarbonate disc layer at the bottom of the structure, which is formed by forming lands and pits.
● The polycarbonate disc layer is covered with a tiny coating of aluminium, which acts as a reflector of laser light.
● An oxidation-resistant lacquer coating is applied to the reflective aluminium layer to protect the layers below it from oxidation.
● It is usually applied immediately on top of the reflective layer using a spin coating process.
● Offset printing or screen printing are used to apply the label print to the lacquer layer, or artwork is screen printed on the top of the disc on the lacquer layer, depending on the application.
How Does a CD Work?
CDs are digitally encoded and contain data or information by utilising a laser beam to create tiny indentations or bumps on the surface of the disc, which is then saved or recorded digitally. The hump is referred to as a pit, and it depicts the number zero. Land is defined as the area of the map where no bump is formed, and it symbolises the number 1 on the map. As a result, the data is encoded onto a compact disc by forming pits (0) and lands (1) on the disc (1). The optically recorded data is read by the CD players by the use of laser technology.
6) DVD (digital video disc):
DVD is an abbreviation for digital versatile disc, which is also known as digital video disc. It is a sort of optical medium that is used for storing optical data and may be found in many different forms. Despite the fact that it is the same size as a CD, its storage capacity is far more than that of a CD. As a result, it is commonly used for a variety of purposes include storing and playing movies, as well as distributing software packages that are too large to put on a CD. In 1995, Sony, Panasonic, Philips, and Toshiba collaborated on the development of the DVD format.
DVDs are classified into the following categories:
DVDs may be split into three categories, which are as follows: educational, entertainment, and home entertainment.
● DVD-ROM (Read-Only): These types of DVDs are pre-loaded with material, such as movie DVDs, and are therefore not read-only.
● Data on these discs cannot be wiped or added, as indicated by the name of the disc; as such, read-only or non-writable DVDs are used to describe them.
● In the case of a DVD-R (Writable), it allows you to record or write information onto the DVD disc. The DVD, however, can only be used to store information until it has been completely filled. After that, it becomes a read-only disc.
● DVD-RW (Rewritable or Erasable): This type of disc has the ability to be erased, written, or recorded several times without losing any information.