ITT Course – Unit I Chapter 4 Auxiliary Storage Devices
Learning Objectives • To discuss various Auxiliary Storage Devices • To know about Magnetic Tape, Winchester Disk, Floppy Disk, etc. • To understand other storage devices like CD-ROM, CD-R Drive, etc.
Auxiliary Storage Device • The main memory construction is costly. Therefore, it has to be limited in size. • The main memory is used to store only those instructions and data which are to be used immediately. • However, a computer has to store a large amount of information. The bulk of information is stored in the auxiliary memory. • Auxiliary memory is also called backing storage or secondary storage. • Auxiliary memory includes hard disk, floppy disks, CD-ROM, USB flash drives, etc. Floppy Disk Digital Video Disk Flash Drive Magnetic Tape Compact Disk Hard Disk
Methods for Secondary Storage • Any method for secondary storage must involve two physical parts which is as follows:- • A peripheral device (the component of the computer which 'reads' in or 'writes' out the information to/from the system unit,) and • An input/output medium, on which the information is actually stored.
Secondary Storage Access • The act of retrieving pieces of stored information is called access. • Access time is the average time taken from the device to search and read the required data on the storage medium. • Shorter access time means higher searching speed.
Sequential Access In sequential access, the items are traversed one by one from the beginning of the sequence to the desired one.
Random Access In random access, also call direct access, any item can be accessed relatively independently of its location in the sequence.
Data Transfer Rate • Data transfer rate is the amount of data that can be transferred between the main memory and a storage device per second. • The unit of data transfer rate is bps (bits per second). • Higher data transfer rate means faster reading / writing process.
Reading Data Steps for reading data from secondary storage devices is shown as follows:-
Writing Data Steps for writing data into secondary storage devices is shown as follows:-
Secondary Storage Medium Following are the mediums used as secondary storage devices:- Magnetic Tapes Optical Disk Magneto-Optical Disk Magnetic Disk
Magnetic Tapes • Magnetic tape is the most popular and oldest storage medium used to store large amount of data and instructions permanently. • The magnetic tape is a plastic ribbon with width 0.25 inch to 1 inch and one side coated with magnetic recording material (ferrous-oxide or iron-oxide), which can be magnetized. Data is stored on the tape in the form of magnetic field, i.e. magnetized and non-magnetized spots representing l’s and 0’s respectively. • Tape remains a viable alternative to disk in some situations due to its lower cost per bit. Small open reel of 9 track tape
Magnetic Tapes (First Recording ) Magnetic tape was first used to record computer data in 1951 on theMauchly - EckertUNIVAC I. The recording medium was a 1/2 inch wide thin band ofnickel-plated bronze. Recording density was 128 characters per inch on eight tracks at a linear speed of 100 ips, yielding a data rate of12,800 characters per second. Making allowance for the empty space between tape blocks, the actual transfer rate was around 7,200 characters per second. UNIVAC I - Tape Units, 1951
Magnetic Disk • A memory device, such as a floppy disk, a hard disk, or a removable cartridge, that is covered with a magnetic coating on which digital information is stored in the form of microscopically small, magnetized needles. • A storage device, consisting of magnetically coated disks, on the surfaces of which information is stored in the form of magnetic spots arranged in a manner to represent binary data.
Tracks and Sectors Tracks and Spots The disk surface is divided into concentric tracks (circles within circles). The thinner the tracks, the more storage. The data bits are recorded as tiny magnetic spots on the tracks. The smaller the spot, the more bits per inch and the greater the storage.Sectors Tracks are further divided into sectors, which hold a block of data that is read or written at one time Tracks and Sectors Tracks are concentric circles on the disk, broken up into storage units called "sectors." The sector, which is typically 512 bytes, is the smallest unit that can be read or written.
Magnetic Disk Summary • Technology Still in use:- • Fixed Hard Disk • Floppy Disk • Zip Removable Disk • REV Removable Disk • Discontinued Technology:- • PocketZip Removable Disk • Jaz Removable Disk • ORB Removable Disk • LS-120 Removable Disk • HiFD Removable Disk • SyQuest Removable Disk • SyJet Removable Disk • SparQ Removable Disk • EZFlyer Removable Disk • Quest Removable Disk • Bernoulli Removable Disk
Floppy Disk • A floppy disk is a data storage medium that is composed of a disk of thin, flexible ("floppy") magnetic storage medium encased in a square or rectangular plastic shell. • Floppy disks are read and written by a FDD (Floppy Disk Drive).
Floppy Drive (Technology) 3½-inch drives Date Invented: 1982 5¼-inch drives Date Invented: 1976 8-inch drives Date Invented: 1969 Invented by IBM team led by David L. Noble
Floppy Disk (Technology) 5¼-inch disk 3½-inch disk 8-inch disk
Floppy Disk (Anatomy) 1. Write-protect tab (open=protected) 2. Hub 3. Shutter 4. Plastic housing 5. Paper ring 6. Magnetic disk 7. Disk sector User can see how the disk is divided into tracks (brown) and sectors (yellow).
Floppy Drive (Anatomy) Drive Motor: A very small spindle motor engages the metal hub at the center of the diskette, spinning it at either 300 or 360 rotations per minute (RPM). Stepper Motor: This motor makes a precise number of stepped revolutions to move the read/write head assembly to the proper track position. The read/write head assembly is fastened to the stepper motor shaft. Mechanical Frame: A system of levers that opens the little protective window on the diskette to allow the read/write heads to touch the dual-sided diskette media. An external button allows the diskette to be ejected, at which point the spring-loaded protective window on the diskette closes.
Floppy Drive (Anatomy) Read/Write Heads: Located on both sides of a diskette, they move together on the same assembly. The heads are not directly opposite each other in an effort to prevent interaction between write operations on each of the two media surfaces. The same head is used for reading and writing, while a second, wider head is used for erasing a track just prior to it being written. This allows the data to be written on a wider "clean slate," without interfering with the analog data on an adjacent track. Circuit Board: Contains all of the electronics to handle the data read from or written to the diskette. It also controls the stepper-motor control circuits used to move the read/write heads to each track, as well as the movement of the read/write heads toward the diskette surface.
Hard Disk Drive • A hard disk drive is a non-volatile storage device that stores digitally encoded data on rapidly rotating platters with magnetic surfaces. • A typical desktop machine will have a hard disk with a capacity of between 10 and 40 gigabytes.
Internal Hard Disk Drive The internal hard disk drives are used for the storage of the data in the computer case. There are not portable and usually are inside the case.
External Hard Disk Drive The external hard disk drives are portable can be connected to other computer systems as well. There is a hard casing over the hard disk.
Measuring Performance of Hard Disk Drive There are two ways to measure the performance of a hard disk: Data rate: The data rate is the number of bytes per second that the drive can deliver to the CPU. Rates between 5 and 40 megabytes per second are common. Seek time: The seek time is the amount of time between when the CPU requests a file and when the first byte of the file is sent to the CPU. Times between 10 and 20 milliseconds are common. The other important parameter is the capacity of the drive, which is the number of bytes it can hold.
First Hard Disk Drive In September 1956 IBM launched the 305 RAMAC, the first computer with a hard disk drive (HDD). The HDD weighed over a ton and stored 5 MB of data. 1956: IBM 305 RAMAC Computer with Disk Drive
Zip Disk and Drive • Zip disks are high capacity, removable, magnetic disks, which can be read or written by ZIP drives. • The Zip drive is a medium-capacity removable disk storage system. • It was introduced in late 1994. • ZIP disks are similar to floppy disks, except that they are much faster, and have a much greater capacity. • ZIP disks are available in size of 100 MB, 250 MB, 750 MB. • ZIP drives are available as internal or external units using SCSI, IDE, Parallel Port interfaces. • The rewritable CDs and rewritable DVDs replaced the Zip drive for mass storage.
USB Drive • A small, portable flash memory card that plugs into a computer’s USB port and functions as a portable hard drive. • A USB flash drive consists of flash memory data storage device integrated with a USB (Universal Serial Bus) interface. • A flash drive consists of a small printed circuit board carrying the circuit elements and a USB connector, insulated electrically and protected inside a plastic, metal, or rubberized case which can be carried in a pocket or on a key chain. • USB flash drives are often used for the same purposes as floppy disks. • USB flash drives have less storage capacity than an external hard drive. • They are smaller, faster, have thousands of times more capacity, and are more durable and reliable. • USB flash drives also are called thumb drives, jump drives, pen drives, key drives, tokens, or simply USB drives.
Inside USB Drive 1 USB connector 2 USB mass storage controller device 3 Test points 4 Flash memory chip 5 Crystal oscillator 6 LED 7 Write-protect switch 8 Space for second flash memory chip
Optical Disk • Optical storage devices are the most widely used and reliable storage devices. • It was introduced in 1982. • These devices use laser technology to store and read data to and from the disk. • An optical storage media consists of a flat, round, portable metal disc, which is coated with a thin metal or plastic or other material that is highly reflective.
1st Generation Optical Disk • Initially, optical discs were used to store music and computer software. The laser disc format stored analog video signals. • Compact Disc (CD) • Laser disc • Magneto-optical disc • Mini disc • DVD
2nd Generation Optical Disk • Second-generation optical discs were for storing great amounts of data, including broadcast-quality digital video. • Hi-MD • DVD and derivatives • DVD-Audio • DualDisc • Digital Video Express (DIVX) • Super Audio CD • Video CD • Super Video CD • Enhanced Versatile Disc • GD-ROM • DataPlay • Phase-change Dual • Universal Media Disc • Ultra Density Optical
3rd Generation Optical Disk • Third-generation optical discs are in development, meant for distributing high-definition video and support greater data storage capacities, accomplished with short-wavelength visible-light lasers and greater numerical apertures. • Currently shipping: • Blu-ray Disc • HD VMD Disc • CBHD Disc • In development: • Forward Versatile Disc • Digital Multilayer Disk / Fluorescent Multilayer Disc • Abandoned: • HD DVD
Next Generation Optical Disk • The following formats go beyond the current third-generation discs and have the potential to hold more than one terabyte (1TB) of data: • Holographic Versatile Disc • LS-R • Protein-coated disc (Layer-Selection-Type Recordable Optical Disk)
Pits and Lands • The information on the optical disk is stored in the form of pits and lands. • The pits are the tiny reflective bumps that are created with laser beam. The lands are flat areas separating the pits. • A land reflects the laser light, which is read as binary digit 1. • A pit absorbs or scatters light, which is read as binary digit 0. • The high-powered laser beam creates the pits. • A lower-powered laser light reads data from the disc. • Like tracks on a magnetic disk, the tracks of an optical disk are divided into sectors but shape of these sectors is different than sectors of magnetic disk.
CD-ROM • CD-ROM stands for Compact Disc Read-Only-Memory. • It was introduced in 1984. • CD-ROM is a type of optical disc that uses laser technology to store and to read data to and from the disc. • A large amount of data can be stored on a single disk. • Once the information is stored on the CD-ROM, it becomes permanent and cannot be changed (altered). The information can only be read for processing. • The CD-ROM is removable and can be used to transfer data from one computer to another like a floppy disk. • A typical CD-ROM has storage capacity from 650 MD to 1GB.
CD-ROM Drive • The CD-ROM drive is used with computer to read the information from the CD-ROM. • Today, CD-ROM drives have transfer rates (or speeds) ranging from 48X to 75X or more.
CD-R • CD-R stands for Compact Disc Recordable which is a blank disk that is used to store information. • It was introduced in 1988. • The user can also write data on an optical disc. • The process of writing data on the optical disc is called burning. • A locally developed CD-R can be used in any CD-ROM drive. • It must be noted that once data is written on the CD-R. It cannot be changed. However, a user can store data on other part of the disk until it is full. Each part of a CD-R can be written only one time and can be read as many times. • The CD-writer is used to write data on CD-R. • The main disadvantage of CD-R is that information can be written only once. These cannot be overwritten and erased.
CD-Writer • A CD-writer or recorder is used to write data on CD-R disks. • Usually, a CD-writer can read information from CD as well as write information on CD. • Today, most of the PCs have CD writer. • The speed of these drives is up to 48X or more. • These drives are more expensive than ordinary CD-ROM.
CD-RW • CD-RW stands for compact Disc Rewritable. • It was introduced in 1996. • The CD-RW is a new generation of optical disk. • It is erasable disc. • The user can write and over-write data on the CD-RW disc many times. • The CD-RW acts like a floppy and hard disk that allow users to write and re-write data. • However, the reliability of the disc tends to decrease, each time you rewrite data.
DVD • DVD stands for Digital Video Disk. • The DVD was developed in 1995. • It was a natural upgrade to the CD. • The DVD capacity is 4.7 GBs for single layer DVDs, and 8.5 GBs for dual layer DVDs. • DVDs resemble Compact Discs in that they have the exact appearance.
DVD-ROM / DVD-R Drive • DVD stands, for Digital Video Disc or Digital Versatile Disc. • DVD-ROM is an extremely high capacity optical disc with storage capacity from 4.7 GB to 17 GB. • DVD disc is specially used to store movie films, huge databases, music, complex software etc. • The DVD-ROM drive is used to read data from DVDs and CDs. • Some DVD-ROMs are double sided and data is stored on both sides of the disc.
DVD-RW • A DVD-RW disc is a rewritable optical disc with equal storage capacity to a DVD-R, typically 4.7 GB. • The primary advantage of DVD- RW over DVD-R is the ability to erase and rewrite to a DVD-RW disc. • According to Pioneer, DVD-RW discs may be written to about 1,000 times before needing replacement, making them comparable with the CD-RW standard. • DVD-RW discs are commonly used for volatile data, such as backups or collections of files.
DVD Writer • DVD Writer is a device which is used to read and display as well as writer contents from / to DVD and CDs.