Secondary memory is also known as secondary storage. The secondary memory is accessed indirectly via input/output operations. This memory is also called permanent, external, stable or persistent memory. It is characterised by its slowness and cheapness, relative to the RAM, and by its permanent appearance.
The CPU does not directly process it. It's content firstly copied into ram and then transferred to CPU. The Secondary memory store data that can be easily retrieved only by the main memory and used by the processor. It is slower than RAM but larger storage capacities than primary memory.
The processed data is, generally, stored in a digital format either on a hard disk drive (HDD) or floppy disk drives, optical drives, tape drives, external hard drives, RAID and USB storage devices, which is called Secondary memory, or removable mass storage devices(MSDs). Primary storage devices are known as Random access memory (RAM), While RAM (Random Access Memory) has fewer data storage capacity, and the data got disappeared when the computer is turned off.
Secondary memory devices are not only convenient for storing backup files, but they also allow computer users to expand their ability to transfer large amounts of data to another Secondary memory devices.
Secondary memory devices are nonvolatile in nature and data does not disappear when the computer turned off and on again. Secondary memory is cheaper than primary memory but is also slower in both reading and writing. Primary memory (RAM) is faster but does not store data permanently, instead of loading secondary memory slower data in the primary memory to make efficient use of it. Unlike primary memory, secondary memory also does not access the CPU directly from the computer.
Magnetic or hard drives are the most common type of secondary memory. All modern computers usually use at least one internal hard disk drive (HDD). These are also frequently attached externally through a Universal Serial Bus (USB), and they also used in redundant and recoverable storage networks in case of accidental loss of data.
Optical storage discs, such as compact discs (CDs) and digital video discs (DVDs), were the initial successors on the secondary hard drive. Their ability to hold much more data and their low cost have been more than enough to compensate for slow write speeds. As technology has improved and media prices have remained low, optical storage remains a viable and accessible medium for portable secondary storage.
Flash memory has seen a surge in popularity and technological progress. It works much like a hard drive concerning access, much faster thanks to the storage media are not sequentially written as a hard disk tray. The flash memory may be considered slow nonvolatile memory, but it is still unable to access the CPU of a computer directly. As its capacity has increased, while its prices have dropped, flash memory has become a direct competitor of hard disk drive (HDD): it has a fast read and writes time and better mechanical stability because it has no moving parts.