Paper 2 CS System Software & Operating System Part 5

Banker’s algorithm is used for Deadlock avoidance.

“● Starvation is method in which process with high priorities continuously uses the resources preventing low priority process to acquire the resources
● In the Shortest job next scheduling shortest job process will run first and later higher burst time.Here the process with higher burst time need to wait for longer time.
“

“Given data,
2 jobs need 10 min CPU time,
50% IO waiting time
Step-1: Here, total CPU time is IO operation time and execution time.
Step-2: We can assume, CPU time = (IO operation time*execution time) =2 times
Step-3: CPU running both the process is 10+10 mins.
1 CPU time=20 mins.
Step-4: Need= 2 times *20 min
=40mins.
Note: Actual answer key, they given Option C
“

Priority scheduling algorithm could result starvation. Starvation is nothing but indefinite blocking.

“A requires 3, B-4, C-6;
→ If A have 2, B have 3, C have 5 then deadlock will occur i.e., 2+3+5=10.
→ If we have one extra resource then deadlock will not occur i.e., 10+1=11.
→ If we have equal (or) more than 11 resources then deadlock will never occur.
“

“→ A dirty bit (or) modified bit is a bit that is associated with a block of computer memory and indicates whether or not the corresponding block of memory has been modified. The dirty bit is set when the processor writes to (modifies) this memory.
→ The bit indicates that its associated block of memory has been modified and has not been saved to storage yet. When a block of memory is to be replaced, its corresponding dirty bit is checked to see if the block needs to be written back to secondary memory before being replaced or if it can simply be removed.
→ Dirty bits are used by the CPU cache and in the page replacement algorithms of an operating system.
→ Dirty bits can also be used in Incremental computing by marking segments of data that need to be processed or have yet to be processed.
“

“→ A context switch (also sometimes referred to as a process switch or a task switch) is the switching of the CPU (central processing unit) from one processor thread to another.
→ Context switches can occur only in kernel mode. Kernel mode is a privileged mode of the CPU in which only the kernel runs and which provides access to all memory locations and all other system resource
→ Other programs, including applications, initially operate in user mode, but they can run portions of the kernel code via system calls
→ The existence of these two modes in Unix-like operating systems means that a similar, but simpler, operation is necessary when a system call causes the CPU to shift to kernel mode. This is referred to as a mode switch rather than a context switch, because it does not change the current process.
→ Context switch between the processes involves mode switch also.”

If the system is deadlocked, it implies that each process is holding one resource and is waiting for one more. Since there are 3 processes and 4 resources, one process must be able to obtain two resources. This process requires no more resources and therefore it will return its resources when done.

“→ Preprocessor is a program that processes its input data to produce output that is used as input to another program.
→ The output is said to be a preprocessed form of the input data, which is often used by some subsequent programs like compilers.
→ The amount and kind of processing done depends on the nature of the preprocessor.
→ Preprocessor is the first module of a language processing system.
“

“→ Page are fitted in frames, so first we need to determine the pages but given request are just the record request in decimal. We can assume that first page to address from 0000 to 0099 and page 2 contains records from 0100 to 0199 and so on (it is given in question that each page contains 100 records) and so on. So page request string is
01, 02, 04, 04, 05, 05, 05, 01, 02, 02, 02, 03, 03.
Clearly 7 page faults.”

“TRUE: Shortest remaining time (SRT) algorithm is the preemptive version of the shortest job next(SJN) CPU scheduling algorithm.
TRUE: A “context switch” is the mechanism to store and restore the state or context of a CPU in PCB.”

“Role of the page table
→ In operating systems that use virtual memory, every process is given the impression that it is working with large, contiguous sections of memory.
→ Physically, the memory of each process may be dispersed across different areas of physical memory, or may have been moved (paged out) to another storage, typically to a hard disk drive.
→ When a process requests access to data in its memory, it is the responsibility of the operating system to map the virtual address provided by the process to the physical address of the actual memory where that data is stored.
→ The page table is where the operating system stores its mappings of virtual addresses to physical addresses, with each mapping also known as a page table entry (PTE).
“

Noncontiguous memory allocation splits programs into blocks of memory called Segments that can be loaded into non adjacent “holes” in main memory.

“→ The 3.5-Inch floppy diskettes have dimensions of 8.9cm in width by 9.3cm in height and are referred to as floppies because of the circular magnetic floppy within the hard shell.
→ 3.5-inch floppy diskettes come in sizes of 720 KB low-density, 1.44 MB high density capacity, and IBM even developed an Extended Density disk capable of holding 2.88 MB.”

“→ Compaction refers to combining all the empty spaces together and processes. Compaction helps to solve the problem of fragmentation, but it requires too much of CPU time.
→ It moves all the occupied areas of store to one end and leaves one large free space for incoming jobs, instead of numerous small ones.
→ In compaction, the system also maintains relocation information and it must be performed on each new allocation of job to the memory or completion of job from memory.”

When process is unable to run until some task has been completed, the process is in blocked state and if process is using the CPU, it is in running state.

“→ fflush() is typically used for output stream only. Its purpose is to clear (or flush) the output buffer and move the buffered data to console (in case of stdout) or disk (in case of file output stream).
→ The two fork() calls create 3 child processes, and hence “”PROCESS”” will be executed 4 times if we don’t use fflush.
→ If we put a ‘\n’ at end of printf or use fflush(stdout); only 1 printf will be done.”

Open count indicates the number of processes that have the file open

The operating system is loaded through a bootstrapping process, more succinctly known as booting. A boot loader is a program whose task is to load a bigger program, such as the operating system.

“● The computer systems Input/output (I/O) architecture is to interface to the outside world.
● Each I/O module interfaces to the system bus and controls one or more peripheral devices.
● The major functions of an I/O module are categorized as follows:
■ Control and
■ Processor
■ Device communication
■ Data buffering
■ Error Detection
“

We will assign one thread for each image so that all images will load faster.

“1. New
A program which is going to be picked up by the OS into the main memory is called a new process.
2. Ready
Whenever a process is created, it directly enters in the ready state, in which, it waits for the CPU to be assigned. The OS picks the new processes from the secondary memory and put all of them in the main memory. The processes which are ready for the execution and reside in the main memory are called ready state processes.
3. Running
One of the processes from the ready state will be chosen by the OS depending upon the scheduling algorithm.
4. Block or wait
From the Running state, a process can make the transition to the block or wait state depending upon the scheduling algorithm or the intrinsic behavior of the process.
“

“● coalescing is the act of merging two adjacent free blocks of memory.
● When an application frees memory, gaps can fall in the memory segment that the application uses.
● Among other techniques, coalescing is used to reduce external fragmentation, but is not totally effective.
● Coalescing can be done as soon as blocks are freed, or it can be deferred until some time later (known as deferred coalescing), or it might not be done at all.
“

“→ A real-time operating system (RTOS) is any operating system (OS) intended to serve real-time applications that process data as it comes in, typically without buffer delays.
→ Processing time requirements (including any OS delay) are measured in tenths of seconds or shorter increments of time.
→ A real time system is a time bound system which has well defined fixed time constraints
→ A multitasking operating system like Unix is poor at real-time tasks. The scheduler gives the highest priority to jobs with the lowest demand on the computer, so there is no way to ensure that a time-critical job will have access to enough resources.
“

“● A path, the general form of the name of a file or directory, specifies a unique location in a file system.
● An absolute or full path points to the same location in a file system, regardless of the current working directory. To do that, it must include the root directory.
● By contrast, a relative path starts from some given working directory, avoiding the need to provide the full absolute path.”