Secondary Memory

Q.       What is secondary storage?

Ans.: Secondary storage: Secondary storage is non-volatile and has lower cost per bit stored, but operates generally at speeds far slower than that of primary storage. Computer systems use it primarily to store large volume of data on permanent basis, which they transfer partially to primary storage, whenever required for processing. Several thousand times higher capacity as compared primary memory. Hard disks, CD ROM are example of secondary memory.

Q.       What are the differences between Primary and Secondary memory?

Ans.:  Difference between primary and secondary memory:  

    

Characteristics	Primary Memory	Secondary Memory
Location with respect to the CPU	Inside/Outside and  directly accessible by CPU	Outside and indirectly accessible by CPU
Cost	Most expensive	Less expensive then primary storage
Capacity	Lower as compared to secondary memory	Several thousand times higher as compared primary memory
Average access time	In billionths of a second	In millionths of a second
Data processing directly form storage	Yes	No. Data must first be moved into primary memory
Means of storing information	Semiconductor chips	Magnetic disk, tape and optical disk

Q.       Write short notes about PROM? 

Ans.: PROM:

·   PROM stands for Programmable Read Only Memory

·   A memory chip whose contents can be programmed by a user or manufacturer for a specific purpose

·   The bit patterns cannot be changed or erased.

Q.       Write short notes about EPROM?

Ans.: EPROM:

·   EPROM stand for Erasable Programmable Read Only Memory

·   A memory chip reprogrammed for other purposes.

·   Erasable Programmable Read Only Memory.

·   Erase data using ultra violet ray.

·   After erasing all data permanently erased.

·   Comparatively cheap.

  

Q.       Write short notes about EEPROM?                             

Ans.:  EEPROM:

·   Electrically Erasable Programmable Read Only Memory.

·   Erase data using electrical method.

·   After erasing all data won’t be lost but lost only selected cell data.

·   Comparatively costly.

Q.       Define magnetic tape.     

Ans.:  Magnetic tape: Magnetic tape is a medium for magnetic recording, made of a thin magnetize able coating on a long, narrow strip of plastic film. It was developed in Germany, based on magnetic wire recording. Devices that record and play back audio and video using magnetic tape are tape recorders and video tape recorders. A device that stores computer data on magnetic tape is a tape drive.

Q.       Define cassette.  

Ans.:  Cassette: The Compact Cassette, also called audio cassette, cassette tape, cassette, or simply tape, is a magnetic tape sound recording format. It was designed originally for dictation, but improvements in fidelity led the Compact Cassette to supplant the Stereo 8-track cartridge and reel-to-reel tape recording in most non-professional applications. Its uses ranged from portable audio to home recording to data storage for early microcomputers.

Q.       Define cartridge.

Ans.:  Cartridge: An ink cartridge or inkjet cartridge is a replaceable component of an inkjet printer that contains the ink (and sometimes the print head itself) that is deposited onto paper during printing. Each ink cartridge contains one or more partitioned ink reservoirs; certain manufacturers also add electronic contacts and a chip that communicates with the printer. Two types of design in cartridge: Thermal and Piezoelectric

·   Thermal: Most consumer inkjet printers, such as those made by Canon, HP, and Lexmark (but not Epson) use a thermal inkjet; inside each partition of the ink reservoir is a heating element with a tiny metal plate or resistor.

·   Piezoelectric: All Epson printers use a piezoelectric crystal in each nozzle instead of a heating element. When current is applied, the crystal changes shape or size, forcing a droplet of ink from the nozzle.

Q.       Name and differentiate the two main categories of storage devices.        

Ans.: Magnetic Storage & Optical Storage.

Magnetic storage: Magnetic storage is a most common storage. A disk is round, flat object that spins around its center. Magnetic disks are almost always housed inside a case of some kind, so you can’t see the disk itself unless you open the case. Read/write heads, which work in much the same way as the heads of a tape recorder or VCR, are used to read data from the disk or write data onto the disk. The device that holds a disk is called a disk drive.

Optical Storage: Optical storage device use laser to read data from or write data to the reflective surface of and optical disk. The CD ROM drive is the most common type of optical storage device.

Q.       Write down the characteristics of hard disk.          

Ans.:  Characteristics of Hard Disk: A computer relies on its hard drive to store nearly everything that it needs to operate, including all of its programs and data. Hard drive capacity has steadily increased while the cost and physical size of the drives have decreased at the same time. At the same time, the general characteristics of the hard drive will remain the same. The following characteristics are given below:

·         Storage Capacity: The capacity of a hard drive is measured in bytes. Modern drive capacities are in the gigabyte (billions of bytes) and terabyte (trillions of bytes) range and likely to go higher.

·         Access Speed: The hard drive is an electro-mechanical device. The data that is stored on the magnetic platters is read by a head that floats just above the surface as the disk rotates beneath it. The combination of the speed of the head movement and how quickly the platter can rotate under the head form the basis for the access speed.

·         Form Factor: Early hard drives were huge, housed in separate machines and connected to the CPU via heavy cables. Modern hard drives are limited to three physical formats: 3.5-inch, 2.5-inch and 1.8-inch. The smaller physical size limits the number of platters and the diameter of those platters.

·         Interface: The electronic connection between the hard drive and processor has undergone a number of changes over time. Each interface change has improved the data transfer speed and ease with which the hard drive is handled by the motherboard in the computer.

Q.       Write down the characteristics floppy disk.           

Ans.:  Characteristics of a Floppy Drive: Floppy drives are a type of disk drive that can read and write to special disks called floppy diskettes, which are like CDs and DVDs in that they hold information.

·         Size: A floppy drive is classified as a 3.5-inch drive, which means that it fits into a 3.5-inch drive by in a computer case. They are shaped like a rectangular prism.

·         Function: The main function of the floppy drive is to read floppy diskettes and write data to them.

·         Uses: Computer users can still use floppy drives and diskettes for storing data that does not require a lot of space. For example, you can store many word processing documents and low-quality pictures, but you will not fit many video or music files onto a floppy diskette.

Q.       Write short notes on optical disk.               

Ans.: Optical disk: The familiar audio compact disk is a popular medium for storing music; the medium is called compact disk read only memory. A CD-ROM drive reads digital data from a spinning disk by focusing a laser on the disk’s surface. Some areas of the disk reflect the laser light into a sensor, and other areas scatter the light. A spot that reflects the laser beam into the sensor is interpreted as a 1, and the absence of a reflection is interpreted as a 0. Data is laid out on a CD-ROM disk in a long, continuous spiral. Data is stored in the form of land, which are flat areas on the metal surface, and pits which are hollows. A land reflects the laser light into the sensor (indicating data bit of 1) and a pit scatters the light (indicating a data bit of 0). A standard CD-ROM can store 650 MB of data or about 70 minutes of audio.

CD-ROM is divided by sectors. Each sector of a drive has own logical label no. The sectors take same amount of time to read data. The first CD-ROM drives could read data at 150 KBps. Now use 2X, 4X, 8X, and so on. 2X means 2*150 = 300 KBps.

Q.       How the storage devices work in a computer?     

Ans.: Whether its punch cards and vacuum tubes or millions of microscopic magnets and transistors, with computing technology comes the necessity of reliable data storage. Despite major strides in their methods and materials, these devices continue to share a common language.

Hard Drive: A hard drive uses an electromagnet to magnetize a group of iron particles, giving them positive and negative poles, according to the PC Guide. It then magnetizes a second group. If the poles of the first and second group face the same direction, the bit is a 0. If they face opposite directions, it's a 1.

RAM: RAM sends electrical impulses along data lines that run to transistors. These either open or close each transistor. Closed transistors allow current to flow into capacitors, which store the charge, whereas open transistors block current. Capacitors with charge represent 1s. Without charge, they represent 0s.

CD: CDs contain impressions that run in a series of peaks and valleys in a continuous spiral. A laser reflects differently from a peak than it does from a valley. The CD drive's optical sensor recognizes this as the difference between 0s and 1s.

DVD: DVDs are similar to CDs except that they pack smaller peaks and valleys into a tighter spiral and can contain two layers of tracks on both sides of the disk. Thus, they can hold up to 25 times the information.

Q.       What are the necessities of formatting a disk?     

Ans.: Before the computer can use a magnetic disk to store data, the disk’s surface must be magnetically mapped so that the computer can go directly to a specific point on it without searching through data. The process of mapping a disk is called formatting or initializing. So, without formatting we can’t use a magnetic disk.

Q.       Calculate the capacity of a hard disk having 1631 cylinders, 12 heads & 60 sectors/ track.

Ans.: We know,

            Number of tracks = No. of cylinders X No. of heads

            Number of sectors = No. of tracks X No. of sectors/track

            Capacity = No. of sectors X 512 bytes/sector

            So the result is:

            Number of tracks = 1631 X 12 = 19,572

            Number of sectors = 19,572 X 60 = 1,174,320

            Capacity = 1,174,320 X 512 = 601,251,840

Q.       Calculate the capacity of hard disk having 32,640 cylinders, 6 heads, 360 sectors/track & 512 bytes/sector.

Ans.: We know, Number of tracks = Number of cylinders X Numbers of heads.

            or,            Number of tracks = 32640 X 6 = 195840 tracks

                              Number of sectors = Number of tracks X Number of sectors/track

            or,            Number of sectors = 195840 X 360 = 70502400 sectors

                              Capacity = Number of sectors X 512 bytes/sector

or,            Capacity = 70502400 X 512 = 3.60972288 X 10¹⁰ = 3.60972288 X 10¹⁰ / (1024 X 1024 X 1024) =33.618 GB

Q.       The capacity of a CD-ROM is 750 MB and the capacity of a floppy disk is 1.4MB. How many floppy disks are equivalent to a CD-ROM?               

Ans.: 750/1.4 = 536

Q.       The capacity of a CD-ROM is 1280689 bits what will be the capacity of this CD-ROM in Megabyte?

Ans.:  We know,

                              8 bit = 1 Byte

            So,

                              1280689 bit = 1280689/8 = 160086.125 Byte

            Again,

                              1024 Byte = 1 KB

            So,

                              160086.125 Byte = 160086.125/1024 = 156.33411 KB

            Again,

                              1024 KB = 1 MB

            So,

                              156.33411 KB = 156.33411/1024 = 0.15267 MB

Q.       Name some popular secondary storage devices used in today’s computer system.

Ans.: Magnetic tape, Cassette, Floppy Disk, Hard Disk, Optical Disk, Magnetic Bubble, Charged-Coupled Devices.