Widgets

widgets

widgets are virtual tools, programmed to share
dynamic information with users. Widgets can be web
based or desktop based. Various third-party sites
offer both types of widgets. When you create a web
widget, the widget provider generates an HTML code
which can be added to your web page code to display
the widget on your website. Desktop widgets are
applications which appear on your desktop and relay
dynamic information. Common desktop widgets
include clocks, calendars, current weather, scorecards etc.
In order to download and install desktop widgets, you would
require a widget engine. A widget engine is an
application with which one can execute and display widgets

Tablet PC

TABLET PC

Tablet PCs are mobile computers that
appear like a notebook or a slate.
Tablet PCs are meant to be mobile
and compact. They come equipped
with additional features like touchscreens
and related technologies
which enables the user to operate the
system with a stylus, a digital pen or
by mere touch instead of peripherals
like mice and keyboards.
Thus, Tablet PC is a general term
used for the pen computing technology.
The term "Tablet PC" was originally
coined by Bill Gates of Microsoft at the
2001 Comdex Conference.

SMART CARD


Smart Cards are pocket-sized cards made of plastic
which contain an embedded chip which contains encoded
data. They are also known as chip cards or integrated
circuit cards (ICC). The data is fed into the chip which
can be used either as an input (for authentication) or
output (like a punch card) with the help of specifically
designed applications. Some smart cards also have an
embedded hologram or other such mechanisms to circumvent
counterfeiting. The usage of smart cards has
risen considerably since it is a form of strong security authentication for
large companies and organizations
dealing with confidential matters.

Spyware

SPYWARE

Spyware is an application that
gathers information from a
person's computer without
their knowledge or consent. It
is also known as a spybot or
tracking software. Spyware
applications are usually used
to send spam to unsuspecting
users. The easiest way to install
a spyware on a users system is
through pop-up windows,
freeware applications or
screensaver packages.
Applications that install themselves
through advertisements
are called adware.
But since marketing companies
raised objections to
the term adware, the
Internet security companies
also refer to such
applications as "potentially
unwanted programs" or
PUP in short.

RESTORE POINT IN Windows Xp

Restore points are saved "snapshots" of the system data at a
given point of time created using the System Restore facility of
Windows. The System Restore feature can be used with Windows
ME, XP and Vista operating systems. The Windows Server family does
not support this feature. When youcreate a restore point,
your computer creates a backup
copy of all data, including the registry files and most drivers
at that particular time. It is wise to create a Restore Point
before you make any major change to your system to save
it from any potential system crashes. But remember that if
you restore your system to an earlier date and then decide to
roll back your system restore, any applications installed
between these two dates will be uninstalled automatically, but
the reqistery entries are not completely removed.

IMEI MEANS

IMEI Means

IMEI stands for International Mobile Equipment Identity. It is a unique number
provided to GSM and 3G enabled mobile handsets. It is usually found underneath
the battery of your cell phone. It enables you to identify whether a particular
mobile handset is fake or an original make. It can only identify the device;
it does not have any bearing to the service provider. You can find out the IMEI of
your mobile by typing *#06# on your GSM or 3G mobile phones. Newer models
equipped with the CDMA equipment uses MEID or Mobile Equipment Identifier

A-GPS

A-GPS is an abbreviation for 'Assisted GPS'. It
enhances the performance of a GPS based satellite.
A-GPS is now available with almost all GPS receivers
including the latest cell phones released in the
market. There are several instances when a GPS
device cannot function properly due to poor signal
conditions especially when it is surrounded by tall
buildings or if it is trying to locate a position when
indoors. An A-GPS receiver can solve and overcome
all these problems. The only difference between
GPS and A-GPS is that the latter uses an assistant
server that increases the processing power and can
locate a position quickly.

Google Wave

Google Wave is an application by Google that collaborates several Google
features. A user who has installed Google Wave will be able to access and use Google
features like Orkut, Google Talk and GMail efficiently. Google Wave can also check for
errors (grammatical and spelling) as well translate text to forty different languages.
Google has not yet announced when Wave will be released. For the user's convenience,
Google will open source part of the code so that users can develop or modify the
features of the program.

Project Natal

microsoft is working on a project known as 'Natal', which on completion would
probably be the new face of gaming. It involves gaming without the use of any
controllers. End users will be able to play games or interact with the interface with
gestures and spoken commands on their existing XBox consoles. The device would be
around nine inches and a motion sensor would be placed either above or below the
display device. It would feature face and voice recognition as well as full body 3D
motion capturing capabilities. Observers are expecting it to be launched in late 2010.

an Accelerometer

An accelerometer is a device that
can measure acceleration forces. For
example, one can find out the angle of
a particular device with respect to its
placement with an accelerometer. This
is done by measuring the amount of
static acceleration due to gravitational
force. The accelerometer that is
embedded in a cell phone senses
motion and detects acceleration
forces. This is how the phone is
controlled. The accelerometer used in
the iPhone and iPhone 3G rotates the
display's orientation to either portrait
or landscape. This motion sensor is also
used for gaming purposes wherein an
object can be moved and controlled
by simply tilting the phone in various
directions. Besides gaming, phones
also use accelerometers to perform
simple tasks like switching between
applications and songs by just a small
flick of the phone. Some other phones
that use the accelerometer for
gaming and other applications include
the Sony Ericsson W760i and K850i and
Nokia's N96.

The history of mobile PC s

1968

Dynabook Alan Kay developed a
portable computer to introduce children to the
electronic media. The graphical user interface with
icons became a prototype for most operating systems
even today.

1981

Osborne 1 The Osborne Computer
Corp was the first to introduce a portable
computer in the market. It weighed more than 10 kilos
and there was no battery. At that time, the software
that it could load using two 5.25-inch floppies
usually cost more than the computer itself

1982

GriD Compass 1100
With a flat screen integrated into the
hinged lid and an ultra-light magnesium
body, Bill Moggridge’s GRiD was the
undisputed technology leader. However at
$10,000, this mobile PC was so expensive
that only the US military and NASA could
afford it.

1983

Compaq Portable
Compaq introduced the first IBMcompatible
laptop into the market. Heavy and without a battery, it did
not sell very well in spite of running the MS-DOS operating system

1984

Gavilan SC Gavilan introduced
the first touchpad which was attached
to the keyboard. The computer had a typical
foldaway form and used an LCD screen as
well as the MS-DOS compatible Intel-80186 cpu.

1985

Bondwell 2 Even though the
CP/M era was over, the Bondwell 2
became a success. With 64 KB of
memory, a 3.5-inch disk drive and an
LCD screen, it was the top dog in the
early laptop scene.

1988

Compaq SLT 286The SLT286 was equipped
with a battery, hard disk and a flat LCD screen.
The screen offered full VGA resolution. It
was mainly bought by businessmen—no wonder,
considering that the purchase price was the
same as a mid-range car.

1997

USB interface After the USB
interface was introduced, almost
every peripheral device could be
connected to a notebook. Portable
devices suddenly became universally
usable.

1999

Wi-Fi for everyone Thanks to wireless
networking, notebooks finally
became fully free of wires. Hotspots
started springing up, connecting
notebooks to the Internet and to
office networks from almost
anywhere.

2008

MacBook Air More than hardware
and software features, physical
design has started to become an important
consideration for buyers. Multitouch
gestures were a great feature, but this
device sold mainly for its looks and attitude.

The most important steps in hard drive development

1956

The first hard disk weighs 500 kg
IBM launches the very first
hard drive, called the IBM
350 (5 MB, 24 inches, 600
ms access time 1,200 rpm,
500 kg, 10 kW). The drive is
rented out for approx 5,000
dollars per month.

1963

Open disk pack The IBM 1311 was
announced on 11th October. It could store
2 million characters on an interchangeable disk
pack (IBM 1316). The disk packs were 4 inches tall,
weighed 4.5 kg each and used 6 14-inch disks with
10 writable surfaces.


1973

Winchester ‘73
IBM launches the “Winchester” project
with the objective of developing a disk
drive in which the rotating medium is
firmly fixed. The loading mechanism is
problematic—that is also why the name
is similar to that of the legendary rifle.

1979

The first 8-inch Winchester
In 1979, industrially manufactured
Winchester disks were introduced.
They were even heavier and
costlier, but the sales only
increased.

1980

The first 5.25-inch drive Seagate brings the ST506
into the market (6MB, 3,600 rpm, selling price:
$1,000).The model label ST506 was the name for
the interface for years.

1986

SCSI specification SCSI became one of
the first standardized I/O protocols for a
hard disk interface.

1989

IDE standardization Western Digital
standardized the Integrated Drive
Electronics protocol.

1997

Giant magnetoresistance First use of the giant
magnetoresistance effect discovered by Peter Grünberg.
IBM overcomes the 10 GB barrier with the DTTA-351680.

2004

Introduction of NC Q Seagate brought the
first SATA hard disk with Native Command Queuing
to the market.

2005

First hybrid drive Samsung created
the HMO8HHI, a 2.5-inch hybrid
disk made out of a magneticmechanical
component and an NAND flash
memory used asa quicker buffer.

2006

Perpendicular recording
The Momentus 5400.3, a 160 GB
large 2.5-inch hard disk from
Seagate used perpendicular
recording technology.

2007
Terabyte hard drive With the Deskstar
7K1000, Hitachi brought the
first 1 Terabyte hard drive to the
market.

check your sony ericsson mobile status and info

check your sony ericsson mobile status and info

( press *,left arrow,*,right arrow,right arrow,*,left arrow,*)

that gives:
service info:
model info
software info
sim lock
configration
service settings:
charging:on/off
service test:
check main display
check led/illumination
check keypad
check speaker
check earphone
check microphone
check viberator
check camera
check flash led
check memory stick
check fm radio
check total call time
check real time clock
check security
text labels:
number of given labels in the mobile phone

Shortcut and its Function

Shortcut and its Function


[C] Compose mail
[O] Open mail
[X] Select mail
[S] Star mail. Press repeatedly to cycle stars.
[1] Report spam
[N] Next mail
[P] Previous mail
[K] Next conversation
[J] Previous conversation
[R] Compose reply
[A] Reply to all
[F] Forward mail
[U] Return to Inbox (or refresh)
[Tab] [Enter] Sends message
[Y] + [O] Archive current mail, go to next
[G] + [A] Go to “All Mail”
[G] + [S] Go to “Starred Mail”
[G] + [C] Go to contacts
[G] + [D] Go to Drafts
[G] + [I] Go to Inbox
/ Go to search box
[Esc] Removes cursor from the current field
[Enter] Opens mail, expansion toggle for conversations

Bluetooth laser virtual keyboard.

Bluetooth laser.virtual keyboard

No, this is not another email forward or any kind of prank gadget. A laser
projected keyboard is really here. The device projects a laser keyboard
on any flat surface, and you can then use it like a normal keyboard. Every
keystroke is even accompanied by the sound of a key-hit as in a traditional
keyboard. Available from thinkgeek.com for $150 (Rs. 7,752).

operating system question & answer

OPERATING SYSTEMS

1.What is an operating system?
An operating system is a program that manages the computer hardware. it act as an intermediate
between a users of a computer and the computer hardware. It controls and coordinates the use of the
hardware among the various application programs for the various users.
2.What is the kernel?
A more common definition is that the OS is the one program running at all times on the computer
,usually called the kernel, with all else being application programs.
3.What are batch systems/
Batch systems are quite appropriate for executing large jobs that need little interaction. The user
can submit jobs and return later for the results. It is not necessary to wait while the job is processed.
4.What is graceful degradation?
In multiprocessor systems, failure of one processor will not halt the system, but only slow it down
by sharing the work of failure system by other systems. This ability to continue providing service is
proportional to the surviving hardware is called graceful degradation.
5.Differentiate Tightly coupled systems and loosely coupled systems?
Loosely coupled systems Tightly coupled systems
Each processor has its own local memory Common memory is shared by many processors
Each processor can communicate with other all
through communication lines
No need of any special communication lines
6.What is real time system?
A real time system has well defined ,fixed time constraints. Processing must be done within the
defined constraints, or the system will fail. It is often used as a control device in a dedicated application.
7.What are privileged instructions?
Some of the machine instructions that may cause harm to a system are designated as privileged
instructions. The hardware allows the privileged instructions to be executed only in monitor mode.
8.What do you mean by system calls?
System calls provide the interface between a process and the operating system. When a system
call is executed, it is treated as by the hardware as software interrupt.
10.What is a process?
A process is a program in execution. It is an active entity and it includes the process stack,
containing temporary data and the data section contains global variables.
11.What is process control block?
Each process is represented in the OS by a process control block. It contain many pieces of
information associated with a specific process.
12.What is schedulers?
A process migrates between the various scheduling queues through out its life time. The OS must
select processes from these queues in some fashion. This selection process is carried out by a scheduler.
13.What are the use of job queues, ready queues and device queues?
As a process enters a system they are put in to a job queue. This queues consist of all jobs in the
system. The processes that are residing in main memory and are ready and waiting to execute are kept on
a list called ready queue. The list of processes waiting for a particular I/O devices kept in the device
queue.
14.What is meant by 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 context switch.
15.What is independent process?
A process is independent it cannot affect Or be affected by the other processes executing in the
system. Any process does not share data with other process is a independent process.
16.What is co-operative process?
A process is co-operating if it can affect or be affected by the other processes executing in the
system. Any process that share data with other process is a co-operating process.
17. What are the benefits OS co-operating process?
**Information sharing.
** Computation speed up.
**Modularity.
**Convenience.
18.How can a user program disturb the normal operation of the system?
**Issuing illegal I/O operation.
**By accessing memory locations with in the OS itself.
**Refusing to relinquish the CPU.
19.State the advantage of multiprocessor system?
#Increased throughput.
#Economy of scale.
#Increased reliability.
20. What is the use of inter process communication.
Inter process communication provides a mechanism to allow the co-operating process to
communicate with each other and synchronies their actions without sharing the same address space. It is
provided a message passing system.
21.What is a thread?
A thread otherwise called a lightweight process (LWP) is a basic unit of CPU utilization, it
comprises of a thread id, a program counter, a register set and a stack. It shares with other threads
belonging to the same process its code section, data section, and operating system resources such as open
files and signals.
22. What are the benefits of multithreaded programming?
The benefits of multithreaded programming can be broken
down into four major categories:
• Responsiveness
• Resource sharing
• Economy
• Utilization of multiprocessor architectures
23.Compare user threads and kernel threads.
User threads
User threads are supported above the kernel and are implemented by a thread library at the user
level. Thread creation & scheduling are done in the user space, without kernel intervention. Therefore
they are fast to create and
manage blocking system call will cause the entire process to block
Kernel threads
Kernel threads are supported directly by the operating system .Thread creation, scheduling and
management are done by the operating system. Therefore they are slower to create & manage compared
to user threads. If the thread performs a blocking system call, the kernel can schedule another thread in
the application for execution
24.What is the use of fork and exec system calls?
Fork is a system call by which a new process is created.Exec is also a system call, which is used
after a fork by one of the two processes to place the process memory space with a new program.
25.Define thread cancellation & target thread.
The thread cancellation is the task of terminating a thread before it has completed. A thread that is
to be cancelled is often referred to as the target thread.For example, if multiple threads are concurrently
searching
through a database and one thread returns the result, the remaining threads might be cancelled.
26.What are the different ways in which a thread can be cancelled?
Cancellation of a target thread may occur in two different
scenarios:
• Asynchronous cancellation: One thread immediately terminates the target thread is called asynchronous
cancellation.
• Deferred cancellation: The target thread can periodically check if it should terminate, allowing the target
thread an opportunity to terminate itself in an orderly fashion.
27.Define CPU scheduling.
CPU scheduling is the process of switching the CPU among various processes. CPU scheduling is
the basis of multiprogrammed operating systems. By switching the CPU among processes, the operating
system can make the computer more productive.
28.What is preemptive and nonpreemptive scheduling?
Under nonpreemptive scheduling once the CPU has been allocated to a process, the process keeps
the CPU until it releases the CPU either by terminating or switching to the waiting state. Preemptive
scheduling can preempt a process which is utilizing the CPU in between its execution and give the CPU
to another process.
29.What is a Dispatcher?
The dispatcher is the module that gives control of the CPU
to the process selected by the short-term scheduler. This function involves:
• Switching context
• Switching to user mode
• Jumping to the proper location in the user program to restart that program.
30.What is dispatch latency?
The time taken by the dispatcher to stop one process and start another running is known as
dispatch latency.
31.What are the various scheduling criteria for CPU scheduling?
The various scheduling criteria are
• CPU utilization
• Throughput
• Turnaround time
• Waiting time
• Response time
32.Define throughput?
Throughput in CPU scheduling is the number of processes that are completed per unit time. For
long processes, this rate may be one process per hour; for short transactions, throughput might be 10
processes per second.
33.What is turnaround time?
Turnaround time is the interval from the time of submission to the time of completion of a
process. It is the sum of the periods spent waiting to get into memory, waiting in the ready queue,
executing on the CPU, and doing I/O.
34.Define race condition.
When several process access and manipulate same data concurrently, then the outcome of the
execution depends on particular order in which the access takes place is called race condition. To avoid
race condition, only one process at a time can manipulate the shared variable.
35.What is critical section problem?
Consider a system consists of 'n' processes. Each process has segment of code called a critical
section, in which the process may be changing common variables, updating a table, writing a file. When
one process is executing in its critical section, no other process can allowed to execute in its critical
section.
36.What are the requirements that a solution to the critical section
problem must satisfy?
The three requirements are
• Mutual exclusion
• Progress
• Bounded waiting
37.Define entry section and exit section.
The critical section problem is to design a protocol that the processes can use to cooperate. Each
process must request permission to enter its critical section. The section of the code implementing this
request is the entry section. The critical section is followed by an exit section. The remaining code is the
remainder section.
38.Give two hardware instructions and their definitions which can be
used for implementing mutual exclusion.
• TestAndSet
boolean TestAndSet (boolean &target)
{
boolean rv = target;
target = true;
return rv;
}
• Swap
void Swap (boolean &a, boolean &b)
{
boolean temp = a;
a = b;
b = temp;
}
39.What is semaphores?
A semaphore 'S' is a synchronization tool which is an integer value that, apart from initialization,
is accessed only through two standard atomic operations; wait and signal.Semaphores can be used to deal
with the n-process critical section problem. It can be also used to solve various Synchronization problems.
40.Define busy waiting and spinlock.
When a process is in its critical section, any other process that tries to enter its critical section
must loop continuously in the entry code. This is called as busy waiting and this type of semaphore is also
called a spinlock,because the process while waiting for the lock.
41.Define deadlock.
A process requests resources; if the resources are not available at that time, the process enters a
wait state. Waiting processes may never again change state, because the resources they have requested are
held by other waiting processes. This situation is called a deadlock.
42.What is the sequence in which resources may be utilized?
Under normal mode of operation, a process may utilize a resource in the following sequence:
• Request: If the request cannot be granted immediately,then the requesting process must wait until it can
acquire the resource.
• Use: The process can operate on the resource.
• Release: The process releases the resource.
43.What are conditions under which a deadlock situation may arise?
A deadlock situation can arise if the following four conditions hold simultaneously in a system:
a. Mutual exclusion
b. Hold and wait
c. No pre-emption
44.What is a resource-allocation graph?
Deadlocks can be described more precisely in terms of a directed graph called a system resource
allocation graph. This graph consists of a set of vertices V and a set of edges E. The set of vertices V is
partitioned into two different types of nodes; P the set consisting of all active processes in the system and
R the set consisting of all resource types in the system.
45.Define request edge and assignment edge.
A directed edge from process Pi to resource type Rj is denoted by PiàRj; it signifies that process
Pi requested an instance of resource type Rj and is currently waiting for that resource. A directed edge
from resource type Rj to process Pi is denoted by RjàPi, it signifies that an instance of resource type has
been allocated to a process Pi. A directed edge PiàRj is
called a request edge. A directed edge RjàPi is called an assignment edge.
46.What are the methods for handling deadlocks?
The deadlock problem can be dealt with in one of the three ways:
a. Use a protocol to prevent or avoid deadlocks, ensuring that the system will never enter a deadlock state.
b. Allow the system to enter the deadlock state, detect it and then recover.
c. Ignore the problem all together, and pretend that deadlocks never occur in the system.
47.Define deadlock prevention.
Deadlock prevention is a set of methods for ensuring that at least one of the four necessary
conditions like mutual exclusion, hold and wait, no preemption and circular wait cannot hold. By
ensuring that that at least one of these conditions cannot hold, the occurrence of a deadlock can be
prevented.
48.Define deadlock avoidance.
An alternative method for avoiding deadlocks is to require additional information about how
resources are to be requested.Each request requires the system consider the resources currently available,
the resources currently allocated to each process, and the future requests and releases of each process, to
decide whether the could be satisfied or must wait to avoid a
possible future deadlock.
49.What are a safe state and an unsafe state?
A state is safe if the system can allocate resources to each process in some order and still avoid a
deadlock. A system is in safe state only if there exists a safe sequence. A sequence of processes
is a safe sequence for the current allocation state if, for each Pi, the resource that Pi can
still request can be satisfied by the current available resource plus the resource held by all the Pj, with j
if no such sequence exists, then the system state is said to be unsafe.
50.What is banker’s algorithm?
Banker’s algorithm is a deadlock avoidance algorithm that is applicable to a resource-allocation
system with multiple instances of each resource type.The two algorithms used for its implementation are:
a. Safety algorithm: The algorithm for finding out whether or not a system is in a safe state.
b. Resource-request algorithm: if the resulting resourceallocation is safe, the transaction is completed and
process Pi is allocated its resources. If the new state is unsafe Pi must wait and the old resource-allocation
state is restored.
51.Define logical address and physical address.
An address generated by the CPU is referred as logical address. An address seen by the memory
unit that is the one loaded into the memory address register of the memory is commonly referred to as
physical address.
52.What is logical address space and physical address space?
The set of all logical addresses generated by a program is called a logical address space; the set of
all physical addresses corresponding to these logical addresses is a physical address space.
53.What is the main function of the memory-management unit?
The runtime mapping from virtual to physical addresses is done by a hardware device called a
memory management unit (MMU).
54.Define dynamic loading.
To obtain better memory-space utilization dynamic loading is used. With dynamic loading, a
routine is not loaded until it is called. All routines are kept on disk in a relocatable load format. The main
program is loaded into memory and executed. If the routine needs another routine, the calling routine
checks whether the routine has been loaded. If not, the relocatable
linking loader is called to load the desired program into memory.
55.Define dynamic linking.
Dynamic linking is similar to dynamic loading, rather that loading being postponed until
execution time, linking is postponed. This feature is usually used with system libraries,such as language
subroutine libraries. A stub is included in the image for each library-routine reference. The stub is a small
piece of code that indicates how to locate the appropriate memory-resident library routine, or how to load
the library if the routine is not already present.
56.What are overlays?
To enable a process to be larger than the amount of memory allocated to it, overlays are used. The
idea of overlays is to keep in memory only those instructions and data that are needed at a given time.
When other instructions are needed, they are loaded into space occupied previously by instructions that
are no longer needed.
57.Define swapping.
A process needs to be in memory to be executed. However a process can be swapped temporarily
out of memory to a backing store and then brought back into memory for continued execution.This
process is called swapping.
58.What are the common strategies to select a free hole from a set of
available holes?
The most common strategies are
a. First fit
b. Best fit
c. Worst fit
59.What do you mean by best fit?
Best fit allocates the smallest hole that is big enough. The entire list has to be searched, unless it
is sorted by size. This strategy produces the smallest leftover hole.
60.What do you mean by first fit?
First fit allocates the first hole that is big enough.Searching can either start at the beginning of the
set of holes or where the previous first-fit search ended. Searching can be stopped as soon as a free hole
that is big enough is found.
61.What is virtual memory?
Virtual memory is a technique that allows the execution of processes that may not be completely
in memory. It is the separation of user logical memory from physical memory. This separation provides
an extremely large virtual memory, when only a smaller physical memory is available.
62.What is Demand paging?
Virtual memory is commonly implemented by demand paging. In demand paging, the pager
brings only those necessary pages into memory instead of swapping in a whole process. Thus it avoids
reading into memory pages that will not be used anyway, decreasing the swap time and the amount of
physical memory needed.
63.Define lazy swapper.
Rather than swapping the entire process into main memory, a lazy swapper is used. A lazy
swapper never swaps a page into memory unless that page will be needed.
64.What is a pure demand paging?
When starting execution of a process with no pages in memory, the operating system sets the
instruction pointer to the first instruction of the process, which is on a non-memory resident page, the
process immediately faults for the page. After this page is brought into memory, the process continues to
execute, faulting as necessary until every page that it needs is
in memory. At that point, it can execute with no more faults.This schema is pure demand paging.
65.Define effective access time.
Let p be the probability of a page fault (0£p£1). The value of p is expected to be close to 0; that
is, there will be only a few page faults. The effective access time is Effective access time = (1-p) * ma + p
* page fault time.ma : memory-access time
66.Define secondary memory.
This memory holds those pages that are not present in main memory. The secondary memory is
usually a high speed disk. It is known as the swap evice, and the section of the disk used for this purpose
is known as swap space.
67.What is the basic approach of page replacement?
If no frame is free is available, find one that is not currently being used and free it. A frame can
be freed by writing its contents to swap space, and changing the page table to indicate that the page is no
longer in memory.
Now the freed frame can be used to hold the page for which the process faulted.
68.What are the various page replacement algorithms used for page
replacement?
• FIFO page replacement
• Optimal page replacement
• LRU page replacement
• LRU approximation page replacement
• Counting based page replacement
• Page buffering algorithm.
69.What are the major problems to implement demand paging?
The two major problems to implement demand paging is developing
a. Frame allocation algorithm
b. Page replacement algorithm
70.What is a reference string?
An algorithm is evaluated by running it on a particular string of memory references and
computing the number of page faults. The string of memory reference is called a reference string.
71.What is a file?
A file is a named collection of related information that is recorded on secondary storage. A file
contains either programs or data. A file has certain "structure" based on its type.
72.List the various file attributes.
A file has certain other attributes, which vary from one operating system to another, but typically
consist of these:Name, identifier, type, location, size, protection, time, date and user identification
73.What are the various file operations?
The six basic file operations are
• Creating a file
• Writing a file
• Reading a file
• Repositioning within a file
• Deleting a file
• Truncating a file
74.What are the information associated with an open file?
Several pieces of information are associated with an open file which may be:
• File pointer
• File open count
• Disk location of the file
• Access rights
75.What are the different accessing methods of a file?
The different types of accessing a file are:
• Sequential access: Information in the file is accessed sequentially
• Direct access: Information in the file can be accessed without any particular order.
• Other access methods: Creating index for the file, indexed sequential access method (ISAM) etc.
76.What is Directory?
The device directory or simply known as directory records information-such as name, location,
size, and type for all files on that particular partition. The directory can be viewed as a symbol table that
translates file names into their directory entries.
77.What are the operations that can be performed on a directory?
The operations that can be performed on a directory are
• Search for a file
• Create a file
• Delete a file
• Rename a file
• List directory
• Traverse the file system
78.What are the most common schemes for defining the logical structure of a directory?
The most common schemes for defining the logical structure
of a directory
• Single-Level Directory
• Two-level Directory
• Tree-Structured Directories
• Acyclic-Graph Directories
• General Graph Directory
79.Define UFD and MFD.
In the two-level directory structure, each user has her own user file directory (UFD). Each UFD
has a similar structure, but lists only the files of a single user. When a job starts the system's master file
directory (MFD) is searched. The MFD is indexed by the user name or account number, and each entry
points to the UFD for that user.
80.What is a path name?
A pathname is the path from the root through all subdirectories to a specified file. In a two-level
directory structure a user name and a file name define a path name.
81.What are the various layers of a file system?
The file system is composed of many different levels. Each level in the design uses the feature of
the lower levels to create new features for use by higher levels.
• Application programs
• Logical file system
• File-organization module
• Basic file system
• I/O control
• Devices
82.What are the structures used in file-system implementation?
Several on-disk and in-memory structures are used to implement a file system
a. On-disk structure include
· Boot control block
· Partition block
· Directory structure used to organize the files
· File control block (FCB)
b. In-memory structure include
· In-memory partition table
· In-memory directory structure
· System-wide open file table
· Per-process open table
83.What are the functions of virtual file system (VFS)?
a. It separates file-system-generic operations from their implementation defining a clean VFS interface. It
allows transparent access to different types of file systems mounted locally.
b. VFS is based on a file representation structure, called a vnode. It contains a numerical value for a
network-wide unique file .The kernel maintains one vnode structure for each active file or directory.
84.Define seek time and latency time.
The time taken by the head to move to the appropriate cylinder or track is called seek time. Once
the head is at right track, it must wait until the desired block rotates under the read-write head. This delay
is latency time.
85.What are the allocation methods of a disk space?
methods of allocating disk space which are widely in use are
a. Contiguous allocation
b. Linked allocation
c. Indexed allocation
86.What are the advantages of Contiguous allocation?
The advantages are
a. Supports direct access
b. Supports sequential access
c. Number of disk seeks is minimal.
87.What are the drawbacks of contiguous allocation of disk space?
The disadvantages are
a. Suffers from external fragmentation
b. Suffers from internal fragmentation
c. Difficulty in finding space for a new file
d. File cannot be extended
e. Size of the file is to be declared in advance
88.What are the advantages of Linked allocation?
The advantages are
a. No external fragmentation
b. Size of the file does not need to be declared
89.What are the disadvantages of linked allocation?
The disadvantages are
a. Used only for sequential access of files.
b. Direct access is not supported
c. Memory space required for the pointers.
d. Reliability is compromised if the pointers are lost or damaged
90.What are the advantages of Indexed allocation?
The advantages are
a. No external-fragmentation problem
b. Solves the size-declaration problems.
c. Supports direct access
91.How can the index blocks be implemented in the indexed allocation scheme?
The index block can be implemented as follows
a. Linked scheme
b. Multilevel scheme
c. Combined scheme
92.Define rotational latency and disk bandwidth.
Rotational latency is the additional time waiting for the disk to rotate the desired sector to the disk
head. The disk bandwidth is the total number of bytes transferred, divided by the time between the first
request for service and the completion of the last transfer.
93.How free-space is managed using bit vector implementation?
The free-space list is implemented as a bit map or bit vector. Each block is represented by 1 bit. If
the block is free,the bit is 1; if the block is allocated, the bit is 0.
94.Define buffering.
A buffer is a memory area that stores data while they are transferred between two devices or
between a device and an application. Buffering is done for three reasons
a. To cope with a speed mismatch between the producer and consumer of a data stream
b. To adapt between devices that have different data transfer sizes
c. To support copy semantics for application I/O
95.Define caching.
A cache is a region of fast memory that holds copies of data. Access to the cached copy is more
efficient than access to the original. Caching and buffering are distinct functions, but sometimes a region
of memory can be used for both purposes.
96.Define spooling.
A spool is a buffer that holds output for a device, such as printer, that cannot accept interleaved
data streams. When anapplication finishes printing, the spooling system queues the corresponding spool
file for output to the printer. The spooling system copies the queued spool files to the printer one at a
time.
97.What are the various disk-scheduling algorithms?
The various disk-scheduling algorithms are
a. First Come First Served Scheduling
b. Shortest Seek Time First Scheduling
c. SCAN Scheduling
d. C-SCAN Scheduling
f. LOOK scheduling
98.What is low-level formatting?
Before a disk can store data, it must be divided into sectors that the disk controller can read and
write. This process is called low-level formatting or physical formatting. Low-level formatting fills the
disk with a special data structure for each sector. The data structure for a sector consists of a header,a data
area, and a trailer.
99.What is the use of boot block?
For a computer to start running when powered up or rebooted it needs to have an initial program
to run. This bootstrap program tends to be simple. It finds the operating system on the disk loads that
kernel into memory and jumps to an initial address to begin the operating system execution. The full
bootstrap program is stored in a partition called the boot blocks, at fixed location on the disk. A disk that
has boot partition is called boot disk or system disk.
100.What is sector sparing?
Low-level formatting also sets aside spare sectors not visible to the operating system. The
controller can be told to replace each bad sector logically with one of the spare sectors.This scheme is
known as sector sparing or forwarding.
SIXTEEN MARK QUESTIONS
1. Explain the various types of computer systems.
Mainframe systems
Desktop systems
Multiprocessor systems
Distributed systems
Clustered systems
Real-time systems
Handheld systems
2. Explain how protection is provided for the hardware resources by the operating system.
Dual mode operation
I/O protection with diagram
Memory protection with diagram
CPU protection
3. What are the system components of an operating system and explain them?
Process management
Main-memory management
File management
I/O management
Secondary storage management
Networking
Protection system
Command-interpreter system
4. What are the various process scheduling concepts
Scheduling queues with diagram
Queueing diagram
Schedulers
Context switch with diagram
5. Explain about interprocess communication.
Message-passing system
Naming
Direct communication
Indirect communication
Synchronization
Buffering
6. Give an overview about threads.
Thread definition
Motivation
Diagram
Benefits
User and kernel threads
7. Explain in detail about the threading issues.
The fork and exec system calls
Cancellation
Signal handling
Threads pools
Thread-specific data
8. Write about the various CPU scheduling algorithms.
First-come, first-served scheduling
Shortest-job-first scheduling
Priority Scheduling
Round-robin scheduling
Multilevel queue scheduling
Multilevel feedback queue scheduling
9.What is critical section problem and explain two process solutions and multiple process solutions?
Critical section problem definition
Two process solutions
Algorithm 1, 2 & 3
Multiple-process solution with algorithm
10.Explain what semaphores are, their usage, implementation given to avoid busy waiting and binary
semaphores.
Semaphore definition
Usage for mutual exclusion and process synchronization
Implementation to avoid spinlock using block and wakeup
Binary semaphores
11.Write about critical regions and monitors.
Critical region definition
Implementation of the conditional-region construct
Monitor definition
Syntax of monitor
Schematic view of monitors
Monitor with condition variables
Monitor solution to dining-philosopher problem
12.Give a detailed description about deadlocks and its characterization
Deadlock definition
Deadlock conditions
Mutual exclusion
Hold and wait
No pre-emption
Circular wait
Resource allocation graph
13.Explain about the methods used to prevent deadlocks
Ensure that at least one of the following does not hold
Mutual exclusion
Hold and wait
No pre-emption
Circular wait
14.Explain the Banker’s algorithm for deadlock avoidance.
Deadlock avoidance definition
Data structures used
Safety algorithm
Resource request algorithm
15.Explain about contiguous memory allocation.
Contiguous allocation
Memory protection with diagram
Memory allocation
First fit
Best fit
Worst fit
Fragmentation
16.Give the basic concepts about paging.
Paging definition
Basic method-page, frame, page table, page number & page offset
Paging hardware diagram
TLB with diagram
Protection-protection bits & valid-invalid bits
17.Write about the techniques for structuring the page table.
Hierarchical paging-two-level & multi-level with diagram
Hashed page table with diagram
Inverted page table with diagram
18.Explain the basic concepts of segmentation.
User view of program
Segmentation definition
Hardware used with diagram-segment table, base, limit & offset
Protection and sharing with diagram
Fragmentation
19.Explain the various page replacement strategies.
Page replacement-basic scheme with diagram
FIFO page replacement
Optimal page replacement
LRU page replacement
LRU approximation page replacement
Counting-based page replacement
Page buffering algorithm
20.What are files and explain the access methods for files?
File definition
Attributes, operations and types
Sequential access with diagram
Direct access
Other access methods-index with diagram
21.Explain the schemes for defining the logical structure of a directory.
Single level directory with diagram
Two level directory with diagram
Tree structured directory with diagram
Acyclic-graph directory with diagram
General graph directory with diagram
22.Write notes about the protection strategies provided for files.
Types of access
Access control list (ACL)
Three classifications-owner, group & universe
Other protection approaches-passwords
23.Write about the kernel I/O subsystem.
I/O scheduling
Buffering
Caching
Spooling & device reservation
Error handling
Kernel data structures
24.Explain the various disk scheduling techniques
FCFS scheduling
SSTF scheduling
SCAN scheduling
C-SCAN scheduling
LOOK scheduling
25.Write notes about disk management and swap-space management.
Disk formatting-low level formatting
Boot block-bootstrap loader, boot block, boot disk & system disk
Bad blocks-sector sparing, sector slipping
Swap-space use
Swap-space location
Swap-space management

ivention

Apple II
The Apple II used to
cost only $3,000 when it
launched—unbelievably
reasonable for the time. 1978
1980
1981
1982
Fax machine
The first fax machines
were used by the post
office in Europe. Each
device was quite huge in
the beginning.
MS-DOS
The first version of the
MS DOS operating system
was launched. It was first
developed for 8086 PCs.
Donkey Kong
Donkey Kong became one of
the most successful video
games figures created by
Nintendo, even before Mario
made his debut.
Sony Walkman
Sony launched the
first Walkman into the
market. By 2004, more
than 200 million such
devices would be sold.
C64
The Commodore 64 was
lovingly known as the
“bread box” to its 22
million dedicated users.
286 processor
Intel put the 80286
processor on the market.

MOZILLA FIREFOX

MOZILLA FIREFOX

The previous version 3.0.9 caused
many computer crashes. The reason is
a memory error, using which even
malicious code can be smuggled in.
SOLUTION: The updated version 3.0.10
does not cause these crashes and
doesn't suffer from memory errors

WHAT IS MICROSOFT AZURE?

WHAT IS MICROSOFT AZURE?






MICROSOFT Azure is an operating system that is available as
a cloud computing service. This service would allow users to use
the operating system and a wide range of applications and tools
from anywhere. It was mainly developed for programmers, so that
they could develop applications using the Microsoft Visual Studio
development environment and the Microsoft .NET Framework. This
platform thus reduces the overall cost of developing an application
since programmers would only pay as they use rather than purchasing the entire
developer kit. In the near future Microsoft promises to add more programming
languages and tools for effi ciency.