Foundation of IT

Secondary Storage Devices

What is Storage Device?

Storage Devices are the data storage devices that are used in the computers to store the data. The computer has many types of data storage devices. Some of them can be classified as the removable data Storage Devices and the others as the non removable data Storage Devices.

Computer Memory?The memory is of two types:

one is the primary memory and the other one is the secondary memory.The primary memory is the volatile memory (RAM)and the secondary memory is the non volatile memory. The volatile memory is the kind of the memory that is erasable and the non volatile memory is the one where in the contents cannot be erased. Basically when we talk about the data storage devices it is generally assumed to be the secondary memory.

What are the secondary Storage

Devices?The secondary memory is used to store the data permanently in the computer. The secondary storage devices are usually as follows: hard disk drives – this is the most common type of storage device that is used in almost all the computer systems. The other ones include the floppy disk drives, the CD ROM, and the DVD ROM. The flash memory, the USB data card etc.

Magnetic tapesMagnetic tape has been used for data storage for over 50 years. When storing large amounts of data, tape can be substantially less expensive than disk or other data storage options. This medium consisting of a thin tape with a coating of a fine magnetic material, used for recording analogue or digital data. A device that stores computer data on magnetic tape is a tape drive. The capacity of tape media are generally on the same order as hard disk drives (The largest being about 5 Terabytes in 2011). Magnetic Tapes Generally transfer data a bit slower than hard drives, however magnetic tapes are cheaper and are more durable

• Drawbacks• Writing and retrieving data is slow.

It uses serial access for reading and writing.• Application• Magnetic tapes are used for application which

requires extremely large storage capacity where speed of access is not an issue. It is commonly used for backups of file servers for computer networks, in a variety of batch processing applications such as reading of bank cheques, payroll processing and general stock control.

Floppy DiskFloppy Disks were an were a ubiquitous form of data storage between 1980's and early 2000's, Floppy disks comes in 3 sizes: 8-inches, 5.5-inches and 3.5-inches. The capacities of Floppy disks vary between 1-2.50 Megabytes and these devices were very slow, reading data at rates of bytes and kbytes/second. However, most are very small and portable.

• Application• Any use where small files such as word processing,

small spreadsheets and databases need to be moved from one computer to another.Useful to backup small data files.

Fixed hard discsA hard disk drive is the device used to store large amounts of digital information in computers. Hard disk drives are used to store operating systems, software, video, music and working data. These are suitable for any application which requires very fast access to data for both reading and writing to.Almost all computers used a fixed hard disc. Used for on-line and real time processes requiring direct access. Used in file servers for computer networks to store large amount of data.

It is a non-volatile, random access digital magnetic data storage device. A hard drive is made up of platters which stored the data, and read/write heads to transfer data. A Hard Drive is generally the fastest of the secondary storage devices, and has the largest data storage capacity, approximately the same as Magnetic Tapes. Hard drives however, are not very portable and are primarily used internally in a computer system. Some persons use hard drives externally as a form of storage and as a substitute for portable storage, hard drives used for these purposes are called external hard drives

Portable hard discsPortable hard discs are good fun because you can carry data about all over the place and transfer information, programs, pictures, etc between computers.This hardware can be connected with laptop, notebook and pc using USB port.Plug and play enable the device more flexible to the user.We can carry any where else due to its smaller size, price and capacity.

• Advantages:• Greatly improved data cargo carrying capacity (relative to

the 1.44 Mb floppy disc).• You don't need to worry about the other person having

the same type of special cartridge drive as yourself.• Disadvantages:• Hard drives have to be handled quite carefully, and when

being transported should be wrapped in something soft and put in a padded bag.

• More expensive than other forms of removable media.• Application• Portable disc discs are used to store very large files which

need transporting from one computer to another and price is not an issue.

Optical backing storage media such as CDs andDVDs

Optical disk is an electronic data storage medium from which data is read and written to by using a low-powered laser beam. It is flat, circular, plastic or glass disk on which data is stored in the form of light and dark pits. There are three basic types of optical disks: Read-only optical disks, Write once read many Optical disks and Rewritable Optical disks. Two main types of optical disks are:CD and DVD

What is Storage Device?• CDs tend to be used for large files (but smaller than 1Gb)

which are too big for a floppy disc to hold such as music and general animation.

• CD ROM/DVD ROM Applications which require the prevention of deletion of data, accidental or otherwise.

• CD R/DVD R Applications which require a single ‘burning’ of data, e.g. CDs - recording of music downloads from the Internet, recording of music from MP3 format, recording of data for archiving or backup purposes. DVDs – recording of film movies and television programs.

• CD RW/DVD RW Applications which require the updating of information and ability to record over old data. Not suitable for music recording but is very useful for keeping generations of files. DVDs have between five and ten times the capacity of CDs.

DVDis an abbreviation of Digital Versatile Disc, and is an optical disc storage media format that can be used for data storage. The DVD supports disks with capacities of 4.7 GB to 17 GB and access rates of 600 KBps to 1.3 MBps. A standard DVD disc store up to 4.7 GB of data. There are two types of DVD's: DVD-ROM and DVD-RW. DVD-ROM are stands for DVD-Read Only Memory and they function the same way Read Only Memory Does. DVD-RW Stards for DVD-Rewritable, these disks can be erased and rewritten at any time.

Flash Drive – Pen driveA flash drive is a small external storage device, typically the size of a human thumb that consists of flash memory. USB flash drives are removable and rewritable reads and writes to flash memory. They are a solid-state storage medium that's both inexpensive and durable. Currently, USB 2.0 flash drives on the market are able to reach a data transfer speed of 480 Mbit/s USB 3.0 has transmission speeds of up to 5 Gbit/s. USB Flash drives vary in sizes from 128 Megabytes to 64 Gigabytes. More commonly used sizes vary from 2 Gigabytes -16 Gigabytes.

Flash Drive – Pen drive

Flash Memory cardsFlash memory is a EEPROM non-volatile computer storage chip. These Memory cards currently vary in sizes between 1 Gigabytes -16 Gigabytes and they transfer data at a rate of approximately 14.65 MB/s. Inexpensive and durable, and are very small. Ithave a size of about 1 inch * 0.75 inch with a thickness of about 2mm. Flash memory cards also have a smaller version which is used within cell phones, digital camera, Tablet Pc etc.,

Flash Memory cards