Secondary Storage Devices

A secondary storage device refers to any non-volatile storage device that is internal or external to the computer. It can be any storage device beyond the primary storage that enables permanent data storage.

A secondary storage device is also known as an auxiliary storage device or external storage.

Secondary storage devices are primarily referred to a storage devices that serve as an addition to the computer’s primary storage, RAM and cache memory. Typically, secondary storage allows for the storage of data ranging from a few megabytes to petabytes. These devices store virtually all programs and applications stored on a computer, including the operating system, device drivers, applications and general user data. Most of the secondary storage devices are internal to the computer such as the hard disk drive, the tape disk drive and even the compact disk drive and floppy disk drive.

Types of Secondary storage Devices in Computers are:

1. Read-only memory (ROM)

Read-only memory (ROM) is a type of storage medium that permanently stores data on personal computers (PCs) and other electronic devices. It contains the programming needed to start a PC, which is essential for boot-up; it performs major input/output tasks and holds programs or software instructions.

Because ROM is read-only, it cannot be changed; it is permanent and non-volatile, meaning it also holds its memory even when power is removed. By contrast, random access memory (RAM) is volatile; it is lost when power is removed.

There are numerous ROM chips located on the motherboard and a few on expansion boards. The chips are essential for the basic input/output system (BIOS), boot up, reading and writing to peripheral devices, basic data management and the software for basic processes for certain utilities.

2. Hard disk drive (HDD)

A hard disk drive (HDD) is a non-volatile computer storage device containing magnetic disks or platters rotating at high speeds. It is a secondary storage device used to store data permanently, random access memory (RAM) being the primary memory device. Non-volatile means data is retained when the computer is turned off.

A hard disk drive is also known as a hard drive.

A hard drive fits inside a computer case and is firmly attached with the use of braces and screws to prevent it from being jarred as it spins. Typically it spins at 5,400 to 15,000 RPM. The disk moves at an accelerated rate, allowing data to be accessed immediately. Most hard drives operate on high speed interfaces using serial ATA (SATA) or serial attached technology. When the platters rotate, an arm with a read/write head extends across the platters. The arm writes new data to the platters and reads new data from them. Most hard drives use enhanced integrated drive electronics (EIDE) including cables and connectors to the motherboard. All data is stored magnetically, allowing information to be saved when power is shut off.

Hard drives need a read only memory (ROM) controller board to instruct the read/write heads how, when and where to move across the platters. Hard drives have disks stacked together and spin in unison. The read/write heads are controlled by an actuator, which magnetically reads from and writes to the platters. The read/write heads float on a film of air above the platters. Both sides of the platters are used to store data. Each side or surface of one disk is called a head, with each one divided into sectors and tracks. All tracks are the same distance from the center of the disk. Collectively they comprise one cylinder. Data is written to a disk starting at the furthest track. The read/write heads move inward to the next cylinder once the first cylinder is filled.

3. Floppy Disk

A floppy disk drive (FDD), or floppy drive, is a hardware device that reads data storage information. It was invented in 1967 by a team at IBM and was one of the first types of hardware storage that could read/write a portable device. FDDs are used for reading and writing on removable floppy discs. Floppy disks are now outdated, and have been replaced by other storage devices such as USB and network file transfer.

A floppy disk commonly came in three sizes, 8 inches, 5.5 inches and 3.5 inches, becoming smaller as the technology advanced. The newer, 3.5-inch version used more cutting-edge technology and held more data than previous models, while the original 8-inch floppy drive was developed to load hardware-level instructions and/or data structures called microcode into the IBM System/370 mainframe. The 8-inch flexible diskette was read-only, held 80 kilobytes of memory and was referred to as a memory disk. Eight-inch floppy drives did not connect to the motherboard, but rotated on a turntable that was run by an idler wheel.

As the floppy disk advanced to a smaller 5.5- and 3.5-inch designs, the FDD changed as well. To accommodate a smaller floppy disk, an FDD had to make aggressive changes by matching the size of the floppy disk drive opening to the size of the floppy disk for compatibility. For many years, the majority of PCs and notebooks had a floppy drive. Using a floppy disk to exchange data between PCs was a standard method for many computer technicians. The floppy disk was one of the most common ways to store adequate amounts of data outside of a computer’s hard drive for personal use because they were inexpensive and easy to carry.

4. CD-ROM

Stands for “Compact Disc Read-Only Memory.” A CD-ROM is a CD that can be read by a computer with an optical drive. The “ROM” part of the term means the data on the disc is “read-only,” or cannot be altered or erased. Because of this feature and their large capacity, CD-ROMs are a great media format for retail software. The first CD-ROMs could hold about 600 MB of data, but now they can hold up to 700 MB. CD-ROMs share the same technology as audio CDs, but they are formatted differently, allowing them to store many types of data.

5. Magnetic Tape

A magnetic tape drive is a storage device that makes use of magnetic tape as a medium for storage.

It uses a long strip of narrow plastic film with tapes of thin magnetizable coating. It is essentially a device which records or perhaps plays back video and audio using magnetic tape, examples of which are tape recorders and video tape recorders.

Magnetic tape drives store data on magnetic tape using digital recording.

The tapes are usually stored on cartridges or cassettes, but for drives that are used as data storage tape backups, the tape is often wound on reels. Magnetic tape is not the most dense data storage medium, but as of 2010 the record for the largest data capacity in magnetic tape was 29.5GB per square inch and the Linear Tape-Open (LTO) supported continuous data transfer rates up to 140 MB/s which was comparable to most hard disks drives.

A tape drive is only able to move tape in a single direction and hence can only provide sequential access storage, unlike a disk drive which may provide random access as well as sequential access.

The reason magnetic tape drives are still in use today, especially as an offline data backup, is because of long archival stability and very favorable unit costs.

6. Cartridge Hard Disk

A typical hard disk is built right into your computer or is housed in a box nearby-and you never see the actual hard disk or take it out of its container. A cartridge hard disk, though, is removable. It works kind of like a giant floppy disk in that it slips into a slot in a special kind of removable hard drive case (actually, it’s more like sliding a video tape into a VCR).

A typical cartridge hard disk holds 44 megabytes (there are also 88s).