Common sizes of floppy disks are 8, 5 ¼, 3 ½ inches.
Figure shows the rigid plastic package used for 3 ½ inch disks.
The disk itself is made of Mylar and coated with magnetic material such as iron oxide. The Mylar disk is only a few thousands of an inch thick. Thus the name floppy when a disk is inserted into a drive unit, a spindle damps in the large centre hole and spin the disk at a constant speed of perhaps 300 as 360 RPM. The data is stored on concentric, circular tracks. There is no standard no. of tracks for any common disks about 40 tracks per side and the new 3 ½ inch disk about 80 track per side early single sided driver recorded data tracks on only one side of disk current double sided disk drive stores data on both side of a disk.
To write data on a track current is passed through coil in the head. This creates a magnetic flux in the iron core of the head. A gap in the iron core allows the magnetic flux to spill out and magnetized a section of magnetic material along the track. Once a reason on the track is magnetized in a particular direction it retains that magnetism.
The floppy disk that we discussed in previous section has advantage that they are inexpensive and removable. However because the disk are flexible the data tracks cannot be put too close together and the rate at which the data can be read off a disk is limited because the floppy disks can be rotated at only 300 or 360 RPM.
The disks in a hard disk system are made MP of metal alloy, coated on both side with magnetic material common hard disk sizes are 3 ½, 5 ¼, 8, 10 ½, 14 and 20 inch. The most hard disk are permanently fastened in a drive mechanism and sealed in a dust free package to increase amount of storage per drive, several disk or platters as they are sometimes called may be stacked with spacers. A separate read-write head is used for each disk surface on disk drives more than one recording surface the tracks are after called cylinders.
Hard disks are more dimensionally stable than floppies, so they can be faster. Large hard disks are rotated at about 3600 RPM. Because of rotational speed in about 10 times that of floppy disks, data is read out 10 times as fast, about 5 to 10m bits/sec.
What is a printer?
A printer is an output device that produces text and graphics on paper.
Impact or Non impact Printer:
In an impart printer the character is formed by physical contact as pressure of print head (hammer) pin or font. Against an ink ribbon onto paper. The dot matrix printer, daisy wheel printer, golf ball printer are all impact printer.
In a non impact printer there is no physical contact of the head with paper or ribbon. The laser printer, thermal, ink jet printer and electrostatic printer are all non impact printer.
Daisy Wheel Printer:
In a daisy wheel printer the print head consists of circular wheel. There are 96 spokes and character arm on the wheel. Each spoke has a raised character (print blocks) imposed at the tip to print a character the wheel is rotated until the petal carrying the desired character is in the front of print space on the paper. Then the solenoid driven hammer strike the petal thereby striking the ribbon and paper. After this the print head is moved to the next column.
The print quality of daisy wheel printer is very good the fonts can be easily interchanged. Speed ranges from 10 to 60 CPS.
Dot Matrix Impact Printer:
Dot Matrix Impact Printer does not print whole character each character is formed by small dots. A matrix usually 7 x 5 is followed to create the character patterns of dot. The print head consists of pins arranged in a vertical column. There is a solenoid corresponding to each pin. The character to be printed has dots in certain positions of matrix. The head moves column by column in the matrix. When head is in one of the column of the matrix all the required dots for that column are formed by striking appropriate pins. Then the head moves to next columns in the matrix are covered one character pattern is complete. The characters created in this fashion are of draft quality.
The dot matrix printer can also print the graphics. Any figure or pattern can be created by forming dots semantically column by column without any hardware change dot matrix printer can be made to print in any language. Color printing can also be achieved by dot matrix printer using different color ribbons. The same line is printed in many passes in different passes different color ribbons are selected. The speed of dot matrix printer in draft mode varies from 100 to 200 CPS. The speed in NLCS mode varies from 25 to 50 CPS. The price of dot matrix printer is lower than that of daisy wheel printer.
WIPRO FX 105, HP 2635….etc are some of the example of impact dot matrix printer.
Advantages of dot matrix printer:
1) Can print on multi-part forms or carbon copies
2) Low printing cost per page
3) Can be used on continuous form paper, useful for data logging
4) Reliable, durable
Disadvantages of dot matrix printer:
2) Limited print quality
3) Low printing speed
4) Limited color printing
Laser Printer operates much like a Xerox Machine Laser is used to create an image on photosensitive drum for this purpose the laser is turned ON or OFF. When it sweeps back and forth cross the drum. The image is inked by applying a toner to the image on the drum then the image is electro statically transferred from drum to paper subsequently hitting is done to fuse the inked image on the paper. Hewlette – Packered laser Jet is one of the popular laser printer.
Laser printer offers both better quality and speed. Text and graphics can be combined and high print speeds like 2000 lines/min can be achieved. The prue of laser is high.
Advantages of laser printers:
1) High resolution
2) High print speed
3) No smearing
4) Low cost per page (compared to inkjet printers)
5) Printout is not sensitive to water
6) Good for high volume printing
Disadvantages of laser printers:
1) More expensive than inkjet printers
2) Except for high end machines, laser printers are less capable of printing vivid colors and high quality images such as photos.
3) The cost of toner replacement and drum replacement is high
4) Bulkier than inkjet printers
5) Warm up time needed
Ink-Jet printer provides better quality print out than dot matrix printer. Its output is very sharp though not to the same level as laser printer output still it is cheap compared to the laser printer. Also ink jet printer can print in color. There are no pins audible instead a matrix of small ink-jets is present. The basic principle involves spraying tiny drops of ink onto the paper. When print head moves across the paper, the jet sprays the ink to form the letters. The dot matrix printer usually has 9 to 24 pins but ink-jet printer usually have 48 to 128 small sets. The print quality specified in terms of dot pen inch. Desk Jet and bubble Jets are standard names used by different printers manufacture for their ink jet printer. Hewlette – Packered, LAND, and EPSON are some popular inkjet printer manufacturer speed of inkjet printer 45000 lines per minute.
Advantages of inkjet printers:
1) Low cost
2) High quality of output, capable of printing fine and smooth details
3) Capable of printing in vivid color, good for printing pictures
4) Easy to use
5) Reasonably fast
6) Quieter than dot matrix printer
7) No warm up time
Disadvantages of inkjet printers:
1) Print head is less durable, prone to clogging and damage
2) Expensive replacement ink cartridges
3) Not good for high volume printing
4) Printing speed is not as fast as laser printers
5) Ink bleeding, ink carried sideways causing blurred effects on some papers
6) Aqueous ink is sensitive to water, even a small drop of water can cause blurring
7) Cannot use highlighter marker on inkjet printouts
Usually thermal printers use special heat sensitive paper. The print head consists of heating element. The characters are printed as a matrix of dots. When a particular heating element is switched ON, corresponding spot on the paper is heated and the spot turns dark. Thus dots are burnt onto the paper thereby creating characters as graphics.
In some thermal printer the paper is normal one but the ribbon is heat sensitive. When the spot on the ribbon is heated a dot of ink is fixed on the spot in the paper. A character is formed by a matrix of dots.
The thermal printer is quiet and print quality is consistent. The running cost is high because of special paper as ribbon.
Hard Disk Formatting
Formatting a Hard Disk usually now involves the three different operations.
1) Low level formatting
3) High level formatting
To do low level formatting (format) we use DEBUG to execute a program supplied by the manufacturer of hard disk controller card. The low level format operation involves telling the controller the coding, number of tracks, number of sections. The number of data bytes per sector etc. In a low level format you also specify the locations of any bad sectors on the disk. These bad sectors then will not be listed as available still another important value we specify in a low level format is the interleave factor. The interleave factor is the number of sectors between consecutively numbered sectors on a track.
An important point about low level formatting is that format generated by a controller card from one manufacturer may not be same as format generated by another one. This means that if you move a hard disk from one controller card to another we usually have to do a low level format with new controller before you can write to the disk.
To partition a hard disk you use the DOS FDISK command. This command allows you to divide a large hard disk into as many as four logical drives. Each partition is assigned a drive identifier such as C:, D:, E: etc. DOS versions before 40 limited the maximum size of each partition to 32 m bytes, but later versions allow partition MP to 2 terabytes each. A sector called partition table at very start of disk stores the start and stop cylinder number for each partition and a pointer to the partition that the system should boat from when pause is turned ON.
To perform high level formatting on a hard disk you execute the DOS FORMAT command for each partition. The FORMAT command sets up the boat record, FAT and directory for that partition is the same way as we described previously for a floppy. If the IS option is specified with the format command, the two system files needed to load the operating system from disk to RAM will automatically be copied to the disk when the formatting is done the rest of DOS files are copied to the boat partition.
Speech Synthesis and Recognition with Computer
Q) Describe the operation of direct digitalization speech synthesis and what are its advantages and disadvantages?
Direct digitization speech synthesis produces the highest quality speech, because it is essentially just a playback of digitally recorded speech to start the word you want the computer to speak is spoken clearly into a microphone. The O/p voltage from the microphone is amplified and applied to the i/p of perhaps a 12 bit A/D converter. One approach at this point might be to simply store the A/D samples for the word in a ROM and read the values out to a D/A converter when you want the computer to speak the word. The difficulty with this approach is that if the samples are taken after enough to produce good speech quality a lot of memory is required to store the samples of a word. To reduce the amount of memory required several speech compression algo are used. These algo are too complex to discuss here, but the basic principle involve storing repeated waveforms only once taking advantage of symmetry in waveforms and not storing values for salient periods. Even with compression however direct digital speech requires considerate memory and a bit rate as high as 64 KB. To further reduce the memory required for direct digital speech, some systems use differential as delta modulation. In these system only a 3 bit or 4 bit code representing how much a sample has changed from last sample is stored in memory instead of storing the complete l2 – bit value. This system works well for audio signals, since they change slowly.
The OKI semiconductors MSM 6388 device contains much of the circuitry needed to digitize and reproduce speech using adaptive differential pulse code modulation (ADPCM). This device contains a microphone preamplifier, A/D converter, D/A converter and some low pass filters. The digital values produced by A/D converter are stored in external memory. About 2605 of speech can be stored in 4m bits of external memory.
Another example of a direct digital synthesis system is the national semiconductor digi talkers for further information consults the data sheets for these devices.
Q) Illustrate LPC synthesizer?
→ LPC (Linear Predictive Code) synthesizer such as that in the Texas instrument “speak and spell” use a digital filter for this type of filter the parameter must be sent from microcomputer are the coefficient for the filter and the pitch for the pulse source. A high quality LPC synthesizer may require as many as 16K bits/sec. An example of currently available LPC speech chip is the 7ITS P50C10.
Q) Format Speech Synthesizer?
→ The format filter speech synthesizes approach uses several resonant as format filters to the message signal from variable frequency signal source and a white noise source.
The figure shows how the frequency of this format filters might be arranged for a male or female wires for this type of system the parameter that must be sent from the computer are the pitch of variable frequency signal. The centre frequency for each format filter and the band width of each format filter the data rate for direct format frequency synthesis is only 1 K bits/sec but the parameter must be determined with complex equipment.
Speech Recoganization is considerably more difficult than speech synthesis. The process is similar to try to recognize human faces with a computer vision system with most speech recognisation system the first step is to train system recognize and store those templates in memory. To produce a template for a word, the intended user speech the word several time into a microphone connected to the system. The system that determine several parentheses or features for each repetition of the word and averages them to produce the actual template.
Different systems extracts different parameters to form the template one of the most common method uses a set of format filters with their control frequency adjusted to match those average speakers. The O/P amplitude to produce a signal proportion to energy in the frequency band.
The pulse train from the O - crossing detector is converted to a proportional voltage so it can be digitalize along with the output from the format voltages.