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Ans1-

1. An operation system is an interface between user and hardware.2. Its a software that supports a computer's basic functions, such as scheduling

tasks, executing applications, and controlling peripherals3. This is a system software always running in our computer.4. Operating system should include web browsers and mail programs but it

Should have let the user to choose whether the user want it or not.

Those that include web browsers and email programs as default, without the

possibility of removing them should not be included in operating system.

5.Web browsers and mail programs will be a security threat to the computer

system, information, files and database coming from the internet or the outersource of the computer is an unauthorized to the operating system.

6.The OS has no clue about that, and it will result for the intrusion of the

unwanted programs in the system which can damage file on the computer, it

can be a reason why OS don't have applications already installed to the system

up until now. It's up to the user whether he will install web browsers and mail

programs in the system manually without the OS commanding on it.

Ans2-

Single-user systems should maximize use of the system for the user. A GUI might

waste CPU cycles, but it optimizesthe users interaction with the system.Thisdepends on the context of efficiency /waste on your computer hardware. We waste

energy by using "sleep" or "instant on" modes, for the convenience of users who -

presumablyare paid for the time they speed on the machine.

We waste energy by passing a NOP (no-operation) through the processor, but we

don't really have a way to power the processor on/off only when all resources and

data needed are available. By placing power on the 'rails' and on the USB bus, weare wasting some resources, but this makes the technology of "plug and play" or

"hot-swap" possible. If we did not have these technologies, it would take time and

effort to install or change devices. We store massive amounts of data on the hard

drive, even storing foreign language translators and other fonts that we might never

use. However, if the occasion came when a user needed those added language

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capabilities - it would take some effort to modify the system in order to

accommodate this

Ans 3-

It will favour i/o bound programs because of relatively short CPU burst request by

them,however,the CPU-bound programs will not starve because the i/o bound

programs will relinquish the CPU relatively often to do their i/o.

Ans 4-

1. Program execution.

The operating system loads the contents of a file into memory and begins its

execution. A user-levelprogram could not be trusted to properly allocate CPU time. The purpose of a

computer systems is to allow the user to execute programs. So the operating

systems provides an environment where the user can conveniently run programs.

The user does not have to worry about the memory allocation or multitasking or

anything. These things are taken care of by the operating systems.Running a

program involves the allocating and deallocating memory, CPU scheduling in case

of multiprocess. These functions cannot be given to the user-level programs. So

user-level programs cannot help the user to run programs independently without

the help from operating systems.

2. I/O operations.

The user need only specify the device and the operation to perform on it, while the

system

converts that request into device- or controller-specific commands.

User-level programs cannot be trusted to only access devices theyshould have access to and to only access them when they are

otherwise unused.

3. File-system manipulation.

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There are many details in file creation, deletion, allocation, and naming that users

should not have to perform. Blocks of disk space are used by files and must be

tracked. Deleting a file requires removing the name file information and freeing the

allocated blocks. Protections must also be checked to

assure proper file access. User programs could neither ensure adherence to

protection methods nor be trusted to allocate only free blocks and deallocate blocks

on file deletion.

4. Communications.

Message passing between systems requiresmessages be turned into packets of information, sent to the network

controller, transmitted across a communications medium, and

reassembled by the destination system. Packet ordering and data

correction must take place. Again, user programs might not

coordinate access to the network device, or they might receive

packets destined for other processes.

5. Error detection.

Error detection occurs at both the hardware and

software levels. At the hardware level, all data transfers must be

inspected to ensure that data have not been corrupted in transit. All

data on media must be checked to be sure they have not changed

since they were written to the media. At the software level, media

must be checked for data consistency; for instance, do the number

of allocated and unallocated blocks of storage match the total

number on the device.

CASES WHEN IT IS IMPOSSIBLE FOR USER-

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1.Program execution -This service could not be handled by the userbecause you need access to the hardware.

2. I/O operations -If therewere not interface provided the user could not

do this on their own.3. File-system manipulation - This means the user does not need toworry about accessing and updating the

file system table. Such access is best

handled by the operating system because

of this complexity.4. Communications - In the case of memory mapping this isextremelybeneficial for the OS to handle access and control

to memory regions. The user could not in this case

access such a system to share the map.5. Error detection -If there is some error on one of the lower levelsthe user is notified so that they can take action.

if there is no memory left on the heap for

instance. The user could not do this because it

is simply too much work for the user.

Ans 5-

A program in Kernel mode can access hardware, but a program in user mode can

not because of kernel. Without kernel if user program fails in someway thehardware may traps in OS.Certain instructions could be executed only when the

CPU is in kernel mode. Similarly, hardware devices could be accessed only when

the program is executing in kernel mode. Control over when interrupts could be

enabled or disabled is also possible only when the CPU is in kernel mode.

Consequently, the CPU has very limited capability when executing in user mode,

thereby enforcing protection of critical resources.

Ans6-These operating systems provide different locking mechanisms depending onthe application developers needs. Spinlocks areuseful for multiprocessorsystems where a thread can run in a busy-loop(for a short period of time) ratherthan incurring the overhead of beingput in a sleep queue. Mutexes are usefulfor locking resources. Solaris 2uses adaptive mutexes, meaning that the mutexis implemented with aspin lock on multiprocessor machines. Semaphores andcondition variables are more appropriate tools for synchronization when a

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resourcemust be held for a long period of time, since spinning is inefficient foralong duration.