• Secondary memory is a permanent storage space to hold a large amount of data.
•  Secondary memory is also known as external memory that representing the various storage media (hard drives, USB, CDs, flash drives and DVDs) on which the computer data and program can be saved on a long term basis.
• However, it is cheaper and slower than the main memory.
• Unlike primary memory, secondary memory cannot be accessed directly by the CPU.
• Instead of that, secondary memory data is first loaded into the RAM (Random Access Memory) and then sent to the processor to read and update the data.
• Secondary memory devices also include magnetic disks like hard disk and floppy disks, an optical disk such as CDs and CDROMs, and magnetic tapes.

Features of Secondary Memory

• Its speed is slower than the primary/ main memory.
• Store data cannot be lost due to non-volatile nature.
• It can store large collections of different types, such as audio, video, pictures, text, software, etc.
• All the stored data in a secondary memory cannot be lost because it is a permanent storage area; even the power is turned off.
• It has various optical and magnetic memories to store data.

Types of Secondary Memory

Hard Disk

• A hard disk is a computer’s permanent storage device.
• It is a non-volatile disk that permanently stores data, programs, and files, and cannot lose store data when the computer’s power source is switched off.
• Typically, it is located internally on computer’s motherboard that stores and retrieves data using one or more rigid fast rotating disk platters inside an air-sealed casing.
• It is a large storage device, found on every computer or laptop for permanently storing installed software, music, text documentation, videos, operating system, and data until the user did not delete.

Floppy Disk

• A floppy disk is a secondary storage system that consisting of thin, flexible magnetic coating disks for holding electronic data such as computer files.
• It is also known as Floppy Diskette that comes in three sizes like 8 inches, 5.5 inches and 3.5 inches.
• The stored data of a floppy disk can be accessed through the floppy disk drive.
• It is the only way through a new program installed on a computer or backup of the information.
• It is the oldest type of portable storage device, which can store data up to 1.44 MB.

Since most programs were larger, that required multiple floppy diskettes to store large amounts of data. Therefore, it is not used due to very low memory storage

CD (Compact Disc)

• A CD is an optical disk storage device, stands for Compact Disc.
• It is a storage device used to store various data types like audio, videos, files, OS, Back-Up file, and any other information useful to a computer.
• The CD has a width of 1.2 mm and 12 cm in height, which can store approximately 783 MB of data size. It uses laser light to read and write data from the CDs.

Types of CDs

• CD-ROM (Compact Disc Read Only Memory): It is mainly used for bulk size mass like audio CDs, software and computer games at the time of manufacture. Users can only read data, text, music, videos from the disc, but they cannot modify or burnt it.
• CD-R (Compact Disc Recordable): The type of Compact Disc used to write once by the user; after that, it cannot be modified or erased.
• CD-RW (Compact Disc Rewritable): It is a rewritable CD disc, often used to write or delete the stored data.
• DVD Drive/Disc
• DVD is an optical disc storage device, stands for Digital Video Display or Digital Versatile Disc.
• It has the same size as a CD but can store a larger amount of data than a compact disc.
• It was developed in 1995 by Sony, Panasonic, Toshiba and Philips four electronics companies.
• DVD drives are divided into three types, such as DVD ROM (Read Only Memory), DVD R (Recordable) and DVD RW (Rewritable or Erasable).
• It can store multiple data formats like audio, videos, images, software, operating system, etc. The storing capacity of data in DVD is 4.7 GB to 17 GB.

Blu Ray Disc (BD)

• Blu Ray is an Optical disc storage device used to store a large amount of data or high definition of video recording and playing other media files.
• It uses laser technology to read the stored data of the Blu-ray Disk.
• It can store more data at a greater density as compared to CD/ DVD.
• For example, compact discs allow us to store 700 MB of data, and in DVDs, it provides up to 8 GB of storage capacity, while Blu-ray Discs provide 28 GB of space to store data.

Pen Drive

• A pen drive is a portable device used to permanently store data and is also known as a USB flash drive.
• It is commonly used to store and transfer the data connected to a computer using a USB port.
• It does not have any moveable part to store the data; it uses an integrated circuit chip that stores the data.
• It allows the users to store and transfer data like audio, videos, images, etc. from one computer to any USB pen drive.
• The storing capacity of pen drives from 64 MB to 128 GB or more.

Cache Memory

• It is a small-sized chip-based computer memory that lies between the CPU and the main memory.
• It is a faster, high performance and temporary memory to enhance the performance of the CPU.
• It stores all the data and instructions that are often used by computer CPUs. It also reduces the access time of data from the main memory.
• It is faster than the main memory, and sometimes, it is also called CPU memory because it is very close to the CPU chip.
• The following are the levels of cache memory.
• L1 Cache: The L1 cache is also known as the onboard, internal, or primary cache. It is built with the help of the CPU. Its speed is very high, and the size of the L1 cache varies from 8 KB to 128 KB.
• L2 Cache: It is also known as external or secondary cache, which requires fast access time to store temporary data. It is built into a separate chip in a motherboard, not built into the CPU like the L1 level. The size of the L2 cache may be 128 KB to 1 MB.
• L3 Cache: L3 cache levels are generally used with high performance and capacity of the computer. It is built into a motherboard. Its speed is very slow, and the maximum size up to 8 MB.

Advantages of Cache Memory

1. Cache memory is the faster memory as compared to the main memory.
2. It stores all data and instructions that are repeatedly used by the CPU for improving the performance of a computer.
3. The access time of data is less than the main memory.

Disadvantage of Cache Memory

1. It is very costly as compared to the Main memory and the Secondary memory.
2. It has limited storage capacity.

Register Memory

• The register memory is a temporary storage area for storing and transferring the data and the instructions to a computer.
• It is the smallest and fastest memory of a computer.
• It is a part of computer memory located in the CPU as the form of registers.
• The register memory is 16, 32 and 64 bits in size.
• It temporarily stores data instructions and the address of the memory that is repeatedly used to provide faster response to the CPU.