Operating System Question and Answers:

1. What are the basic functions of an operating system? - Operating system controls and 
coordinates the use of the hardware among the various applications programs for various uses. 
Operating system acts as resource allocator and manager. Since there are many possibly 
conflicting requests for resources the operating system must decide which requests are allocated 
resources to operating the computer system efficiently and fairly. Also operating system is 
control program which controls the user programs to prevent errors and improper use of the 
computer. It is especially concerned with the operation and control of I/O devices. 

2. Why paging is used? - Paging is solution to external fragmentation problem which is to permit 
the logical address space of a process to be noncontiguous, thus allowing a process to be 
allocating physical memory wherever the latter is available. 

3. While running DOS on a PC, which command would be used to duplicate the entire 
diskette? diskcopy 

4. What resources are used when a thread created? How do they differ from those when a 
process is created? - When a thread is created the threads does not require any new resources to 
execute the thread shares the resources like memory of the process to which they belong to. The 
benefit of code sharing is that it allows an application to have several different threads of activity 
all within the same address space. Whereas if a new process creation is very heavyweight 
because it always requires new address space to be created and even if they share the memory 
then the inter process communication is expensive when compared to the communication 
between the threads. 

5. What is virtual memory? - Virtual memory is hardware technique where the system appears to 
have more memory that it actually does. This is done by time-sharing, the physical memory and 
storage parts of the memory one disk when they are not actively being used. 

6. What is Throughput, Turnaround time, waiting time and Response time? – 
1. Throughput : number of processes that complete their execution per time unit. 
2. Turnaround time: amount of time to execute a particular process. 
3. Waiting time; amount of time a process has been waiting in the ready queue. 
4. Response time: amount of time it takes from when a request was submitted until the first 
response is produced, not output (for time-sharing environment). 

7. What is the state of the processor, when a process is waiting for some event to occur? - 
Waiting state 

8. What is Dispatcher? - Dispatcher module gives control of the CPU to the process selected by 

the short-term scheduler; this involves: Switching context, Switching to user mode, Jumping to 

the proper location in the user program to restart that program, dispatch latency ‚ time 

it takes for the dispatcher to stop one process and start another running. 

9. What is CPU Scheduler? - Selects from among the processes in memory that are ready to 

execute, and allocates the CPU to one of them. CPU scheduling decisions may take place when a 

process: 1.Switches from running to waiting state. 2.Switches from running to ready state. 

3.Switches from waiting to ready. 4.Terminates. Scheduling under 1 and 4 is non-preemptive. 

All other scheduling is preemptive. 

10. What is Context Switch? - Switching the CPU to another process requires saving the state of 

the old process and loading the saved state for the new process. This task is known as a context 

switch. Context-switch time is pure overhead, because the system does no useful work while 

switching. Its speed varies from machine to machine, depending on the memory speed, the 

number of registers which must be copied, the existed of special instructions(such as a single 

instruction to load or store all registers). 

11. What is cache memory? - Cache memory is random access memory (RAM) that a computer 

microprocessor can access more quickly than it can access regular RAM. As the microprocessor 

processes data, it looks first in the cache memory and if it finds the data there (from a previous 

reading of data), it does not have to do the more time-consuming reading of data from larger 

memory. 

12. What is a Safe State and what is its use in deadlock avoidance? - When a process requests an 

available resource, system must decide if immediate allocation leaves the system in a safe state. 

System is in safe state if there exists a safe sequence of all processes. Deadlock Avoidance: 

ensure that a system will never enter an unsafe state. 

13. What is a Real-Time System? - A real time process is a process that must respond to the events 

within a certain time period. A real time operating system is an operating system that can run real 

time processes successfully 

14. What is hard disk and what is its purpose? - Hard disk is the secondary storage device, which 

holds the data in bulk, and it holds the data on the magnetic medium of the disk.Hard disks have 

a hard platter that holds the magnetic medium, the magnetic medium can be easily erased and 

rewritten, and a typical desktop machine will have a hard disk with a capacity of between 10 and 

40 gigabytes. Data is stored onto the disk in the form of files. 

15. What is fragmentation? Different types of fragmentation? - Fragmentation occurs in a 

dynamic memory allocation system when many of the free blocks are too small to satisfy any 

request. External Fragmentation: External Fragmentation happens when a dynamic memory 

allocation algorithm allocates some memory and a small piece is left over that cannot be 

effectively used. If too much external fragmentation occurs, the amount of usable memory is 

drastically reduced. Total memory space exists to satisfy a request, but it is not 

contiguous. Internal Fragmentation: Internal fragmentation is the space wasted inside of 

allocated memory blocks because of restriction on the allowed sizes of allocated blocks. 

Allocated memory may be slightly larger than requested memory; this size difference is memory 

internal to a partition, but not being used

+Process Diagram Of Electricity Generation+

Top 50 Engineering Inventions of the Past 5 Decades:

1955—TV REMOTE CONTROL

It marks the official end of humanity's struggle for survival and the beginning of its quest for a really relaxing afternoon. The first wireless remote, designed by Zenith's Eugene Polley, is essentially a flashlight. When Zenith discovers that direct sunlight also can change channels on the remote-receptive TVs, the company comes out with a model that uses ultrasound; it lasts into the 1980s, to the chagrin of many a family dog. The industry then switches to infrared.

1955—MICROWAVE OVEN

In 1945 Raytheon's Percy Spencer stands in front of a magnetron (the power tube of radar) and feels a candy bar start to melt in his pocket: He is intrigued. When he places popcorn kernels in front of the magnetron, the kernels explode all over the lab. Ten years later Spencer patents a "radar range" that cooks with high-frequency radio waves; that same year, the Tappan Stove Co. introduces the first home microwave model.

1957—BIRTH-CONTROL PILL

Enovid, a drug the FDA approves for menstrual disorders, comes with a warning: The mixture of synthetic progesterone and estrogen also prevents ovulation. Two years later, more than half a million American women are taking Enovid—and not all of them have cramps. In 1960 the FDA approves Enovid for use as the first oral contraceptive.

1958—JET AIRLINER 

The Boeing 707-120 debuts as the world's first successful commercial jet airliner, ushering in the era of accessible mass air travel. The four-engine plane carries 181 passengers and cruises at 600 mph for up to 5280 miles on a full tank. The first commercial jet flight takes off from New York and lands in Paris; domestic service soon connects New York and Los Angeles.

1959—FLOAT GLASS

There's a reason old windowpanes distort everything: They were made by rapidly squeezing a sheet of red-hot glass between two hot rollers, which produced a cheap but uneven pane. British engineer Alastair Pilkington revolutionizes the process by floating molten glass on a bath of molten tin—by nature, completely flat. The first factory to produce usable float glass opens in 1959; an estimated 90 percent of plate glass is still produced this way.

1961—CORDLESS TOOLS

Black and Decker releases its first cordless drill, but designers can't coax more than 20 watts from its NiCd batteries. Instead, they strive for efficiency, modifying gear ratios and using better materials. The revolutionary result puts new power in the hands of DIYers and—thanks to a NASA contract—the gloves of astronauts.

1961—INDUSTRIAL ROBOT

The Unimate, the first programmable industrial robot, is installed on a General Motors assembly line in New Jersey. Conceived by George C. Devol Jr. to move and fetch things, the invention gets a lukewarm reception in the United States. Japanese manufacturers love it and, after licensing the design in 1968, go on to dominate the global market for industrial robots.

1962—COMMUNICATIONS SATELLITE 

Telstar is launched as the first "active" communications satellite—active as in amplifying and retransmitting incoming signals, rather than passively bouncing them back to Earth. Telstar makes real a 1945 concept by science fiction author Arthur C. Clarke, who envisioned a global communications network based on geosynchronous satellites. Two weeks after Telstar's debut, President Kennedy holds a press conference in Washington, D.C., that is broadcast live across the Atlantic.

1962—LED 

Working as a consultant for General Electric, Nick Holonyak develops the light-emitting diode (LED), which provides a simple and inexpensive way for computers to convey information. From their humble beginnings in portable calculators, LEDs spread from the red light that indicates coffee is brewing to the 290-ft.-tall Reuters billboard in Times Square.

1964—UNMANNED AERIAL VEHICLES

Widespread use of remotely piloted aircraft begins during the Vietnam War with deployment of 1000 AQM-34 Ryan Firebees. The first model of these 29-ft.-long planes was developed in just 90 days in 1962. AQM-34s go on to fly more than 34,000 surveillance missions. Their success leads to the eventual development of the Unmanned Aerial Vehicles widely used today.

1962/VIDEO GAMES MIT programmers write Spacewar; 43 years later 89 percent of school-age kids own video games. 1955/POLIO VACCINE The year Jonas Salk finds a way to prevent polio, there are 28,985 global cases; by 2005, the number drops to 1200. 1957/THREE-POINT SEATBELT According to the U.S. Department of Transportation, more than 15,000 American lives are saved in 2005 by Nils Bohlin's device.

The first general-purpose computer, the nearly 30-ton ENIAC (1947), contains 18,000 vacuum tubes, 70,000 resistors and 10,000 capacitors. In 1959, the INTEGRATED CIRCUIT puts those innards on one tiny chip. Before the entire world is networked, there is the ARPANET—four computers linked in 1969. It introduces the concept of "packet switching," which simultaneously delivers messages as short units and reassembles them at their destination. The Apple II, Commodore Pet and Radio Shack's TRS-80 are introduced in 1977—four years before IBM, soon to become synonymous with the term "PC," unveils its PERSONAL COMPUTER. In 1989, Sir Tim Berners-Lee creates "hypertext markup language" (HTML) to make Web pages and the "Uniform Resource Locator" (URL) to identify where information is stored. These breakthroughs form the foundation of the WORLD WIDE WEB. 

1964—MUSIC SYNTHESIZER 

Robert Moog develops the first electronic synthesizer to make the leap from machine to musical instrument. Moog's device not only generates better sounds than other synthesizers, it can be controlled by a keyboard rather than by punch cards. The subsequent acceptance of electronic music is a crucial step in developing audio technology for computers, cellphones and stereos.

1966—HIGH-YIELD RICE 

The International Rice Research Institute in the Philippines releases a semi-dwarf, high-yield Indica variety that, in conjunction with high-yield wheat, ushers in the Green Revolution. Indica rice thrives in tropical regions of Asia and South America, raising worldwide production more than 20 percent by 1970.

1969—SMOKE DETECTOR 

Randolph Smith and Kenneth House patent a battery-powered smoke detector for home use. Later models rely on perhaps the cheapest nuclear technology you can own: a chunk of americium-241. The element's radioactive particles generate a small electric current. If smoke enters the chamber it disrupts the current, triggering an alarm.

1969—CHARGE-COUPLED DEVICE 

Bell Labs' George Smith and Willard Boyle invent a charge-coupled device (CCD) that can measure light arriving at a rate of just one photon per minute. Smith and Boyle's apparatus allows extremely faint images to be recorded, which is very useful in astronomy. Today, its most noticeable impact is in digital cameras, which rely on CCD arrays containing millions of pixels.

1970—DIGITAL MUSIC 

James Russell, a scientist with the Pacific Northwest National Laboratory, invents the first digital-to-optical recording and playback system, in which sounds are represented by a string of 0s and 1s and a laser reads the binary patterns etched on a photosensitive platter. Russell isn't able to convince the music industry to adopt his invention, but 20 years later, Time Warner and other CD manufacturers pay a $30 million patent infringement settlement to Russell's former employer, the Optical Recording Co.

1971—WAFFLE-SOLE RUNNING SHOES 

Bill Bowerman, the track coach at the University of Oregon, sacrifices breakfast for peak performance when he pours rubber into his wife's waffle iron, forming lightweight soles for his athletes' running shoes. Three years later, Bowerman's company, Nike, introduces the Waffle Trainer, which is an instant hit.

IN THEIR WORDS

1962 Computer Mouse

"I don't know why we call it a mouse. It started that way, and we never changed it." —Doug Engelbart, engineer, Stanford Research Institute, 1968

1969 Automated Teller Machine

"On Sept. 2, our bank will open at 9:00 and never close again!" —Long Island branch of Chemical Bank, advertisement from 1969

1973 Cellphone

"Joel, I'm calling you from a real cellular phone." —Martin Cooper, leader of Motorola's cellphone team, to Joel Engel, research head of rival AT&T's Bell Labs, April 3, 1973

1978 In-Vitro Fertilization

"We'd love to have children of our own one day. That would be such a dream come true." —Louise Brown Mullinder, the first test-tube baby, on her wedding day, in 2003

1979 Sony Walkman

"This is the product that will satisfy those young people who want to listen to music all day." —Akio Morita, Sony Chairman, February 1979

RADICAL FIBERS

From easy-on shoes to lighter tennis rackets and stronger planes, revolutionary materials have changed our lives.

In 1955, Patent No. 2,717,437 is issued to George de Mestral for VELCRO, a fabric inspired by burrs that stick to his dog's fur. In 1961 researchers in Japan develop high-quality CARBON-FIBER COMPOSITES, capping a decade of experimentation with plastics reinforced by carbon fibers. Thanks to DuPont's Stephanie Kwolek and Herbert Blades, who in 1965 invent a high-strength polymer called KEVLAR, the body armor of 2920 police and correctional officers has protected them from fatal attacks. The term "FIBEROPTIC" is coined in 1956, but it isn't until 1970 that scientists at Corning produce a fiber of ultrapure glass that transmits light well enough to be used for telecommunications. 

1972—ELECTRONIC IGNITION 

Chrysler paves the way for the era of electronic—rather than mechanical—advances in automobiles with the electronic ignition. It leads to electronic control of ignition timing and fuel metering, harbingers of more sophisticated systems to come. Today, these include electronic control transmission shift points, antilock brakes, traction control systems, steering and airbag deployment.

1973—MRI

Everyone agrees that magnetic resonance imaging (MRI) is a brilliant invention—but no one agrees on who invented it. The physical effect that MRIs rely on—nuclear magnetic resonance—earns various scientists Nobel Prizes for physics in 1944 and 1952. Many believe that Raymond Damadian establishes the machine's medical merit in 1973, when he first uses magnetic resonance to discern healthy tissue from cancer. Yet, in 2003, the Nobel Prize for medicine goes to Peter Lauterbur and Peter Mansfield for their "seminal discoveries." The topic of who is the worthiest candidate remains hotly debated.

1978—GPS 

The first satellite in the modern Navstar Global Positioning System (GPS) is launched. (The GPS's precursor, TRANSIT, was developed in the early 1960s to guide nuclear subs.) It is not until the year 2000, though, that President Clinton grants nonmilitary users access to an unscrambled GPS signal. Now, cheap, handheld GPS units can determine a person's location to within 3 yards.

1981—SCANNING TUNNELING MICROSCOPE 

By moving the needle of the scanning tunneling microscope (STM) across a surface and monitoring the electric current that flows through it, scientists can map a surface to the level of single atoms. The STM is so precise that it not only looks at atoms—it also can manipulate them into structures. The microscope's development earns IBM researchers Gerd Binnig and Heinrich Rohrer a Nobel Prize and helps launch the emerging era of nanotechnology.

1984—DNA FINGERPRINTING 

Molecular biologist Alec Jeffreys devises a way to make the analysis of more than 3 billion units in the human DNA sequence much more manageable by comparing only the parts of the sequence that show the greatest variation among people. His method quickly finds its way into the courts, where it is used to exonerate people wrongly accused of crimes and to finger the true culprits.

USES

1958/LASER BEAM Whitens teeth, removes tattoos, corrects vision, scans groceries, tracks missiles. 1978/GENETIC ENGINEERING Produces insulin, creates vaccines, clones sheep, increases shelf life of tomatoes, manipulates human cells to prevent disease. 1958/SUPER GLUE Repairs a broken taillight, reassembles a vase, strengthens knots on a hammock, closes wounds, lifts fingerprints.

LIFESAVERS

Over the past 50 years, a few pivotal medical discoveries have helped to boost adult life expectancy dramatically.

In 1956, Wilson Greatbatch grabs the wrong resistor and connects it to a device he is building to record heartbeats. When the circuit emits a pulse, he realizes the device can be used to control the beat; in 1960 the first PACEMAKER is successfully implanted in a human. Rene Favaloro performs the first CORONARY BYPASS SURGERY in 1967, taking a length of vein from a leg and grafting it onto the coronary artery. This allows blood to flow around the blocked section. Thanks in part to these advances, the number of deaths from heart disease declines in the U.S. by almost 50 percent. The outlook for people infected by HIV also dramatically changes. The FDA approves Invirase, the first of a class of drugs called HIV PROTEASE INHIBITORS, in 1995. By blocking the function of enzymes used in the virus's replication, the inhibitors can reduce HIV to undetectable levels for sustained periods in up to 90 percent of patients.

1985—POLYMERASE CHAIN REACTION 

Biochemist Kary Mullis invents a technique that exploits enzymes in order to make millions of copies of a tiny scrap of DNA quickly and cheaply. No matter how small or dried-out a bloodstain is, forensic scientists can now gather enough genetic material to do DNA fingerprinting. With PCR, doctors also can search for trace amounts of HIV genetic code to diagnose infection much sooner than by conventional methods.

1987—PROZAC 

Prozac becomes the first in a new class of FDA-approved antidepressants called "selective serotonin re-uptake inhibitors," which block the reabsorption of the mood-elevating neurotransmitter serotonin, thereby prolonging its effects. Though at times controversial, Prozac helps patients cope with clinical depression, reshaping our understanding of how personality and emotion can be chemically controlled. Within five years, 4.5 million Americans are taking Prozac—making it the most widely accepted psychiatric drug ever.

1998—GENETIC SEQUENCING 

Scientist Craig Venter announces that his company will sequence the entire human genome in just three years and for only $300 million—12 years and $2 billion less than a federally funded project established to do the same thing. Venter uses a method called "shotgun sequencing" to make automated gene sequencers, instead of relying on the laborious approach used by the government program. The result is an acrimonious race to the finish, which ends in a tie. Both groups announce the completion of the human genome sequence in papers published in 2001.

1998—MP3 PLAYER

Depending on who you ask, the MP3 is either the end of civilization (record companies) or the dawn of a new world (everyone else). The Korean company Saehan introduces its MPMan in 1998, long before Apple asks, "Which iPod are you?" When the Diamond Rio hits the shelves a few months later, the Recording Industry Association of America sues—providing massive publicity and a boost to digital technology.

2002—IEEE 802.16

The geniuses at the Institute of Electrical and Electronics Engineers publish a wireless metropolitan area network standard that functions like Wi-Fi on steroids. An 802.16 antenna can transmit Internet access up to a 30-mile radius at speeds comparable to DSL and cable broadband. When it all shakes out, 802.16 could end up launching developing nations into the digital age by eliminating the need for wired telecommunications infrastructure.