Internet technology of Storage organization

Unlike magnetic disks, which have several concentric tracks, an optical disk has one long   track, which starts at the outer edge and spirals inward to the center (see figure). This spiral track is ideal for reading large blocks of sequential data, such as music. However, it makes for slower random access time than the concentric tracks used by  magnetic disks, whose sectors can be located faster because they are always found on a given track at a fixed distance from the center.

              Like a track on a magnetic disk, the track of an optical disk is split up into sectors but with optical disks, each sector has the same length, regardless of whether it is located near the disks center or away from the center. This type of data organization allows data to be packed at maximum density over the entire disk. However, it also requires a more complicated drive mechanism because the rotation speed of the disk must vary inversely with the radium, the drive must slow down the disks rotation speed to read sectors towards the outside of the disk and speed it up to read sectors towards the center of the disk.

The cost-per –bit of storage is very low for optical disk because of their low cost and enormous storage density. They come in various sizes, ranging from 12-inch to 4.7 inch In diameter. The most popular is of 5.25 inch diameter whose capacity is around 650 megabytes. This storage capacity is equivalent to about 250000 pages of printed text or total capacity of 550 double sided, high-density floppy of the same size. This tremendous storage capacity makes optical disks the most suitable storage media for multimedia application. As optical disk have a single track, their storage capacity is multiple of the number of sectors and number of bytes per sector.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              

Internet technology of Winchester disks

A Winchester disk also consists of multiple (two or more)hard disk platters mounted on a single central shaft. However, the main difference between a Winchester disk and a disk pack is that Winchester disks are of fixed type. That is, the hard disk platters and the disk drive are sealed together in a contamination free container  and cannot be separated from each other. Hence as opposed to disk packs, which have virtually unlimited capacity, Winchester disks have limited capacity. However, for the same number of disk platter of the same size, Winchester disks can manage to have larger storage capacity than disk packs due to the following reasons.

       Because both the disk platters and the disk drive are sealed in a contamination free container and do not require to be separated later, all the surfaces of all the disk platter(including the upper surface of the topmost platter and the lower surface of the bottommost platter) are used for data recording in case of Winchester disks. That is for a Winchester disk with four platters, there are eight surfaces on which data can be recorded as opposed to six surfaces in case of a disk pack with four platters.

              The contamination-free environment allows Winchester disks to employ much greater precision of data recording and accessing resulting in greater density of data storage than the interchangeable disk packs.

          The storage capacity of today Winchester disks is usually of the order of a few tens of megabytes to a few gigabytes (10 bytes).          

Internet of access mechanism

Data are recorded on the tracks of a spinning disk surface and read from the surface by one or more read write heads. As shown in figure 6.4 the read write heads are mounted on an access arms assembly. Most disk drives have a single read write head for each disk surface. However some faster disk systems use multiple heads on each access arm to read a number of adjacent tracks simultaneously.

     The access arms assembly can be moved in and out In the direction shown in the figure 6.4 so that the read write head can be moved horizontally across the surface of the disk. In this manner the read write heads can be positioned on any track on which data are to be recorded or from which data are to be read.

The read write heads are of flying type. That is they do not have direct contact with the disk surface. This prevents wear on the surface of the disk. A separation of about 0.00002 inch is maintained between a read write head and its corresponding disk surface. In fact read write heads fly so close to the disk surface that , if a dust particle(typically of 0.0015 inch size), smoke particle (typically of 0.00025 inch size), finger print (typically of 0.00062 inch size) or a human hair (typically of 0.003 inch size) were placed on the disk surface, it would bridge the gap between the write heads and disk surface, causing the head to crash. A head crash, in which the head touches the disk, destroys the data stored in the crash and can destroy a read write head as well.

Internet of data cartridge

Digital audio tape is a type of magnetic tape that uses a same technology as helical scan to record data. A data cartridge is slightly larger than a credit card in width and height and contains a magnetic tape that can hold from 2 to 24 gb of data. it  can support data transfer rate of about 2 mbps. Like other types, data are sequential access media.

          Hard disks are used for on line secondary storage device for most computer systems today. The introduction of high capacity disks for microcomputer systems solved two problems related to the limited storage capacity of diskettes.

    First as a business began to use microcomputers extensively the amount of software acquired and data collected grew up substantially. Now a  day hard disks having capacity of several gb is available. So storage of huge amount of data is no problem.

   Secondary the largest file that could be accessed at one time was limited to the capacity of main memory and the storage medium. Since the capacity of hard disk is virtually unlimited, there is not constraint of accessing to any length of file.

  Data is stored in the same way as it on diskettes. A series of tracks are divided into sectors when the disk is formatted. As their name suggests, hard disks are made out of a rigid substance that is capable of storing a greater amount of data than the soft material used for diskettes. Hard disk drivers for microcomputer can be internal (built into the computer cabinet)or external (outside the computer cabinet and connected to it by a short cable).

Internet of Sequential and direct access device

Several i device can be used as a secondary storage, but the one selected for a particular application, mainly depends upon how the stored information needs to be access. There are two accessing information sequential or serial access and direct or random access.

             Sequential access storage device is one in which the arrival at the location desired may be   preceded by sequencing through other location, so that access time varies according to location. in other words, information on a sequential access device can only be retrieved in the same sequence in which it is stored. Sequential processing is quite suitable for such application like preparation of monthly pay slips, or monthly electricity bills etc. where most if not of all the data record need to be processed one after another.

  In these application, data record for every employee or customer needs to be processed at scheduled intervals in this case monthly. However while working with a sequential access device, if an address is required which out of order, if can only be reached by searching through all those addresses which are stored before it.

Internet the Organization of a main memory having N words

You might have heart about 8 bit computer, 16 bit computer, 32 bit computers etc. This refers to the word length of the memory of a particular computer in terms of total number of bits per memory words. word length is an important architectural factor. Small machines have word length of 8,16 or 32 bits whereas large machines have word word lengths of 64 bits or more. what is the advantage of having more number of bits per word.

                   For the answer to the above question, if you have as 8 bits compute, if means that the word length of your computer is one byte, so the processor can access one byte 8 bit of data at a time. In a 16 bit computer the word length is two byte so the processor can access two bytes 16 bits memory to fetch the data to the cpu through  cache memory. Cache  memory if faster than the main memory.

Internet a floating Point representation

In floating point representation not only they are stored but the position of the decimal point is also taken  into consideration and stores separately.

                The actual number is termed as the mantissa and the decimal (binary) point is termed as the exponent. Depending upon the number system base or radix is assumed to be present but not defined.

                Foe example, if we have to represent 8.49, we can write it as 849 c 10-2 . This type of representation is called the scientific representation. Using this scientific representation, any number can be expressed as a combination of a mantissa and an exponent, or in other words, the number can be expressed as where is the mantissa is the radix of the number system and in the exponent.

                             Now converting the given number to the scientific from, we take.