Can things be this romantic...!!??

Somewhere in my dreams I hear your voice

Whispering gently....into thin air

At the edge of the mountain I close my eyes

Sensing your breathing...feeling you appear there

On the edge of my dreams I see your face

A twin soul......when we share eyes

At the edge of the mountain I catch my breath

Touching our finger tips...mouth goes dry

In the shadows of my dreams I taste your lips

So soft against mine like a warm rain

At the edge of the mountain my heart slows

Sharing our every breath....two hearts don't refrain

In the deepest part of my dreams I feel your touch

Breathless....from the warmth of your skin

At the edge of the mountain I open my eyes

Seeing only clouds....feeling.... within

On the edge of my dreams is where I want to stay

It's there...I'm forever in your arms...safe...sound

At the edge of the mountain I'll remain breathless

For me.....no greater love will ever be found

Will you always be there on the edge of my dreams?

Will you always meet me to the edge of the mountain?

I will wait for you...be there for you....always.

What is multi-processing? What is multi-tasking? What is multi-threading? What is multi-programming?

Multi tasking, programming and time sharing are variations of the same thing.

Single tasking is a system where once a programme starts, no other programme can run until it has ended. Eg early home computers, you loaded a prog. ran it then moved on to the next prog.

Multi tasking/programming/ time sharing is where several progs are running at the same time, but only 1 prog is actually being worked on at any moment in time. The system will share its time between progs that need some action, but always only 1 prog at a time. If a prog needs data from disk/ram it will wait for the data to arrive. This time is used to work on other progs that already have the data needed. The earliest versions of this merely "time sliced" or shared equally between progs whether they needed time or not.

Multi processing is where you have, for example, 2 processors that allows work to be done on 2 progs at the same time. Big servers start at 32 processors and go up from there.

Lets say that you need to add 2 numbers, the hardware sequence runs something like:-
    Fetch the instruction
    Decode it
    fetch the 1st number from memory store in a register
    fetch the 2nd number etc etc
    add the 2 numbers and store the result in another register.

Multi threading allows several parts of the program to be processed without waiting for the first instruction to finish.

In the above example, each step is undertaken by a different part of the hardware, so when our instruction above has been fetched, it goes away and fetches the next instruction, so all the steps of instructions are working their way through a "pipeline". Modern processors have multi pipelines to make things even quicker. This is why some processors with a lower clock speed can out perform other CPUs. This effectively simulates multiprocessing as different progs can be in different pipelines (hyperthreading).

It is not unusual to have multiple processors, with multiple pipelines working on 1 prog. Usually something like weather forcasting where lots of similar data from many sources needs manipulating.

What is memory-mapped I/O? How is it different from I/O mapped I/O?

Memory-mapped I/O, meaning that the communication between the I/O devices and the processor is done through physical memory locations in the address space. Each I/O device will occupy some locations in the I/O address space. i.e., it will respond when those addresses are placed on the bus. The processor can write those locations to send commands and information to the I/O device and read those locations to get information and status from the I/O device.

Memory-mapped I/O makes it easy to write device drivers in a high-level language as long as the high-level language can load and store from arbitrary addresses.

What are demand- and pre-paging ?

With demand paging, a page is brought into memory only when a location on that page is actually referenced during execution. 
With pre-paging, pages other than the one demanded by a page fault are brought in. The selection of such pages is done based on common access patterns, especially for secondary memory devices.

What did you understand by term COMPACTION ?

Compaction refers to the mechanism of shuffling the memory portions such that all the free portions of the memory can be aligned (or merged) together in a single large block.OS to overcome the problem of fragmentation, either internal or external, performs this mechanism, frequently.

Compaction is possible only if relocation is dynamic and done at run-time, and if relocation is static and done at assembly or load-time then compaction is not possible.

What is cycle stealing?

We encounter cycle stealing in the context of Direct Memory Access (DMA). Either the DMA controller can use the data bus when the CPU does not need it, or it may force the CPU to temporarily suspend operation. The latter technique is called cycle stealing. 
Note that cycle stealing can be done only at specific break points in an instruction cycle.

What are turnaround time and response time?

Turnaround time is the interval between the submission of a job and its completion.

Response time is the interval between submission of a request, and the first response to that request.

In the context of memory management, what are placement and replacement algorithms?

Placement algorithms determine where in available real-memory to load a program. Common methods are first-fit, next-fit, best-fit.

Replacement algorithms are used when memory is full, and one process (or part of a process) needs to be swapped out to accommodate a new program. The replacement algorithm determines which are the partitions to be swapped out.

Define latency, transfer and seek time with respect to disk I/O ?

Seek time is the time required to move the disk arm to the required track.

Rotational delay or latency is the time it takes for the beginning of the required sector to reach the head.

Sum of seek time (if any) and latency is the access time.

Time taken to actually transfer a span of data is transfer time.

What are the typical elements of a process image?

Ø User data: Modifiable part of user space. May include program data, user stack area, and programs that may be modified.
Ø User program: The instructions to be executed.
Ø System Stack: Each process has one or more LIFO stacks associated with it. Used to store parameters and calling addresses for procedure and system calls.

Ø Process control Block (PCB): Info needed by the OS to control processes.

What did you understand by Thrashing?

Thrashing is also known as a high-paging activity. It is a phenomenon in virtual memory schemes when the processor spends most of its time swapping pages, rather than executing instructions. This is due to an inordinate number of page faults.

Explain Belady's Anomaly ?

Also called FIFO anomaly. Usually, on increasing the number of frames allocated to a process' virtual memory, the process execution is faster, because fewer page faults occur. Sometimes, the reverse happens, i.e., the execution time increases even when more frames are allocated to the process. This is Belady's Anomaly. This is true for certain page reference patterns.

List the Coffman's conditions that lead to a Deadlock ?

There are the 4 conditions which if occured together then only the system would be in Deadlocked condition, these are:

Ø Mutual Exclusion: Only one process may use a critical resource at a  time.
Ø Hold & Wait: A process may be allocated some resources while waiting for others.
Ø No Pre-emption: No resource can be forcible removed from a process holding it.

Ø Circular Wait: A closed chain of processes exist such that each process holds at least one resource needed by another process in the chain.

What did you understand by Spinlocks and How are they different from Semaphores ?

There are two main types of kernel locks. The fundamental type is the spinlock(include/asm/spinlock.h), which is a very simple single-holder lock: if you can't get the spinlock, you keep trying (spinning) until you can. Spinlocks are very small and fast, and can be used anywhere.

The second type is a semaphore (include/asm/semaphore.h): it can have more than one holder at any time (the number decided at initialization time), although it is most commonly used as a single-holder lock (a mutex). If you can't get a semaphore, your task will put itself on the queue, and be woken up when the semaphore is released. This means the CPU will do something else while you are waiting, but there are many cases when you simply can't sleep and so have to use a spinlock instead e.g. in interrupt service routines.

What is a binary semaphore? What is its use?

A binary semaphore is one, which takes only 0 and 1 as values.

They are used to implement mutual exclusion and synchronize concurrent processes.

Explain the concept of Reentrancy ?

It is a useful, memory-saving technique for multiprogrammed timesharing systems. A Reentrant Procedure is one in which multiple users can share a single copy of a program during the same period. 
Reentrancy has 2 key aspects: The program code cannot modify itself, and the local data for each user process must be stored separately. Thus, the permanent part is the code, and the temporary part is the pointer back to the calling program and local variables used by that program. Each execution instance is called activation. It executes the code in the permanent part, but has its own copy of local variables/parameters. The temporary part associated with each activation is the activation record. Generally, the activation record is kept on the stack.

 Note: A reentrant procedure can be interrupted and called by an interrupting program, and still execute correctly on returning to the procedure.

What is the resident set and working set of a process?

Resident set is that portion of the process image that is actually in real-memory at a particular instant. 
Working set is that subset of resident set that is actually needed for execution. (Relate this to the variable-window size method for swapping techniques.)

What did you understand by the term Translation Lookaside Buffer (TLB)?

n a cached system, the base addresses of the last few referenced pages is maintained in registers called the TLB that aids in faster lookup.TLB contains those page-table entries that have been most recently used.
Normally, each virtual memory reference causes 2 physical memory accesses-- one to fetch appropriate page-table entry, and one to fetch the desired data. Using TLB in-between, this is reduced to just one physical memory access in cases of TLB-hit.

What did you understand by short-, long- and medium-term scheduling ?

Long term scheduler determines which programs are admitted to the system for processing. It controls the degree of multiprogramming. Once admitted, a job becomes a process.

Medium term scheduling is part of the swapping function. This relates to processes that are in a blocked or in a suspended state. They are swapped out of real-memory until they are ready to execute. The swapping-in decision is based on memory-management criteria.

 Short term scheduler, also know as a dispatcher executes most frequently, and makes the finest-grained decision of which process should execute next. This scheduler is invoked whenever an event occurs. It may lead to interruption of one process by preemption.

Headstrong Corporation - Immoral Management?

Incorporated in Virginia and having offshore development centres in Manila, Noida and Bangalore, Headstrong employees were sent an email that no increments will be there in 2009 citing the global downturn and talked about how the Management was leading from the front and not taking any increase on their salaries. However it did not disclose that the Indian Management awarded itself $8m bonus inOctober this year out of the blue.

Do employees have any legal recourse against such unscrupulous managements worldover who are trying to take advantage of the downturn to either fire people or make them slog hard without expecting any wage increases?

Satyam blacklisted by World Bank

Hi,

What I heard what that Satyam sought World Bamk's apology andrequested it to lift its ban for 8 years.But World Bank spurned the apology.

It seems Satyam has reacted in defence by accusing World Bank. Sad to hear an Indian company earning bad name  because of  the practices followed by it.

Important!! For MDI applicants..

Please check if your MDI applications are in order at http://www.mdi.ac.in/home/important_admissios_related_information.asp.