Tertiary Storage Devices - Removable Disks

Tertiary storage or tertiary memory, provides a third level of storage. Typically it involves a robotic mechanism which will mount (insert) and dismount removable mass storage media into a storage device according to the system's demands; this data is often copied to secondary storage before use. It is primarily used for archival of rarely accessed information since it is much slower than secondary storage (e.g. 5–60 seconds vs. 1-10 milliseconds). This is primarily useful for extraordinarily large data stores, accessed without human operators.
Examples : Removable disks, magnetic tapes, CD-ROMs etc.

Removable Disks : A removable disk is a type of media that enables a user to easily move data between computers without having to open their computer. Examples :

* Floppy diskettes : A Floppy Disk Drive, or FDD for short, is a computer disk drive that enables a user to easily save data to removable diskettes. They are made from a thin flexible disk coated with magnetic material, enclosed in a protective plastic case/
* CD disc/DVD disc/Blu-ray disc : A compact disc is a flat round storage medium that is read by a laser in a CD-ROM drive. The standard CD is capable of holding 72 minutes of music or 650 MB of data. 80 minute CDs are also commonly used to store data and are capable of containing 700 MB of data.
Digital Versatile Disc or Digital Video Disc, DVD or DVD-ROM is a type of disc drive that allows for large amounts of data on one disc the size of a standard Compact Disc.
Blu-ray Disc, BD or BD-ROM is an optical disc that is capable of storing up to 25 GB on a single layer disc and 50 GB on a dual layer disc.
* Tape drive cartridges : A magnetically thin coated piece plastic wrapped around wheels that is capable of storing data. Tape is much less expensive than other storage mediums but commonly a much slower solution that is commonly used for backup.
* Thumb drives : It is a portable drive that is often the size of your thumb that connects to the computer USB port. Today flash drives are available in various sizes including but not limited to 256MB, 512MB, 1GB, 5GB, 16GB, and beyond and are widely used as an easy and small way to transfer AND store information from their computer.

High Level Formatting

The second formatting step is high-level formatting. This is the process of creating the disk's logical structures such as the file allocation table and root directory. The high-level format uses the structures created by the low-level format to prepare the disk to hold files using the chosen file system.

Method of formatting a hard disk drive that initializes portions of the hard disk drive and creates important file system areas on the disk. A good example of a high-level format is using the format command in MS-DOS.

A high-level format is commonly done if a user wishes to erase the hard disk drive and reinstall the operating system back onto the hard disk drive. If errors are present on the hard disk drive, or a high-level format is unable to be completed, a low-level format may need to be done first.

For a hard disk, there is an intermediate task that is performed between the two formatting steps: partitioning. For this reason, combined with the incredible complexity of modern hard disks, they are low-level formatted by the manufacturer, and high-level formatting is done by the DOS FORMAT command (or equivalent). Floppy disks require no intermediate step, and due to their relative simplicity, they are both low-level and high-level formatted at the same time by default when you use the FORMAT command.

Disk Formatting and Low level formatting of floppy disks

Disk formatting is the initial part of the process for preparing a hard disk or other storage medium for its first use. The disk formatting includes setting up an empty file system. A disk formatting may setup multiple file systems by formatting partitions for each file system. Disk formatting is also part of a process involving rebuilding an entire disk from scratch.

There are two steps involved in formatting magnetic media such as floppy disks and hard disks.

Low-level formatting of floppy disks : The first step involves the creation of the actual structures on the surface of the media that are used to hold the data. This means recording the tracks and marking the start of each sector on each track. This is called low-level formatting, and sometimes is called "true formatting" since it is actually recording the format that will be used to store information on the disk. Once the floppy disk has been low-level formatted, the locations of the tracks on the disk are fixed in place. Since floppies use a stepper motor to drive the head actuator, the floppy drive must be aligned properly in order to read the tracks on the disk. Sometimes the heads of a particular drive can become out of alignment relative to where they should be; when this happens you may notice that a disk formatted on the misaligned drive will work in that drive but not in others, and vice-versa.
Since floppy disks tend to be put together cheaply these days and many of them are getting rather old, it is generally preferable to always low-level format a disk in the drive you plan to use to write to it.