Operating System Chapterwise Notes of Galvin:Process

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Here we are giving chapter wise notes of operating system based on operating system concepts by galvin

PROCESS


q) what is a process?
a) a program in execution.

q) what is difference b/w the program and process?
a) program is passive entity,such as contents of file on disk. whereas process is a active entity, with program counter
indicating next instruction to be executed, and has set of associated resources.

q) how many states can a process be in?
a) 1)new 2)running 3)waiting 4)ready 5)terminated.

q) what is process control block?
a) each process in o.s is represented by process control block. it contains all information related to process. it contains:-
1) process state
2) program counter
3) cpu registers:- state of process is saved
4) cpu scheduling information:- process priority, pointers to scheduling queues.
5) memory management information:- limit and base registers, page tables.
6) accounting information:- amount of cpu and real time used.
7) i/o status information:- list of i/o devices allocated and list of open files.

q) what is ready queue?
a) processes that are in memory and are ready and are waiting to get executed are kept on list called ready queue, generally
implemented as linked list.

q) what is there in the ready queue?
a) process control blocks.

note:- there is device queue also for each device.

q) what is queueing daigram?
a) it is used to represent process scheduling,ie rectangles for queues,circles for resources etc.

q) how many types of schedulers are there?
a) in batch system, more processes are submitted than can be executed. they are spooled to disk. now we have long-term-
scheduler that selects process from the pool and load into memory. cpu or short-term scheduler selects process from memory
to be given cpu.cpu scheduler needs to take decision fast.

q) when is long term scheduler invoked?
a) when a process leaves the system.

note:- long-term scheduler must send proper mix of i/o bound and cpu bound processes to the memory.

q) which systems donot have long term scheduler?
a) time sharing systems like unix. new process is put in memory for cpu scheduler.

q) what is medium level scheduler?
a) it brings in the concept of swapping.

q) what is context switch?
a) to switch cpu to another process, needs saving state of old process and loading saved state of new process.

q) what is system call to create a new process?
a) create-process.

note:- child processes may get different resouces from its parent process or they may share resources.

q) in unix , how to create new process?
a) each process has a pid, and new process are created by fork system call.

q) what are types of concurrent processes in the system?
a) they may be independent(do not share data) or may be cooperating(share data).

q) why process cooperation is needed?
a) 1) information sharing:- shared file.
2) computation speed up:- task broken into subtasks.here we need multiple processing elements.
3) modularity

q) give examples of the producer consumer problem?
a) print program produce characters to be used by printer driver.compiler produces assembly code for assembler.

note:- a synchonization is required between producer and consumer. a buffer is required in between shared by both.

q) where do we get buffer from?
a) may programmer need to code it , or provided by o.s through use of IPC facility.

q) what is IPC?
a) it is inter process communication facility. it allows processes to communicate without sharing same address space.it is
mostly used in distributed systems. it is provided by message passing system. ex: chat program on WWW.

q) where is message passing used in computer?
a) in b/w micro kernels.

q) what operations do IPC provide?
a) at least 2 ie send(message) and recieve(message).

q) what is direct communication?
a) here we have:-
1) send(P,message):- send a message to process P.
2) recieve(Q,message):- receive a message from process Q.

q) what is indirect communication?
a) here messages are sent to and recieved from mailboxes,or ports.2 processes need to share a mailbox. it works as:-
1) send(A,message):- send a message to mailbox A.
2) recieve(A,message):- receive a message from mailbox A.

note:- mailbox can be owned by a process or by operating system.in second case o.s allows processes to create,send and
recieve and then delete a mailbox.

q) how many ways of message passing?
a) it can be blocking and non-blocking, also called as synchronous and asynchronous. it can be:-
1) blocking send
2) non blocking send
3) blocking recieve
4) non blocking recieve


q) what is rendezvous?
a) when both send and recieve are blocking ,then there is rendezvous b/w sender and reciever.

q) what is buffering here?
a) messages exchanged b/w processes reside in temporary queue. this queue can be implemented in 3 ways:-
1) 0 capacity:- no message should wait,so sender need to get blocked till recipient recieves.
2) bounded capacity:- sender need to block if queue is full.
3) unbounded capacity:- sender never blocks.

q) what is socket?
a) it is defined as end point for communication. processes communicating over network employ it.it is made up of IP address
concatenated with port number.
in genaral sockets use client-server architecture.

q) what are the ports that server listens to provide certain services?
a) telnet server listens to port 23
ftp server listens to port 21
http server listens to port 80.

note:- all ports below 1024 are used for standard services.

q) when a client process request for connection, what happens?
a) it is assigned port number >1024 by host computer. then connection will cosist of pair of sockets. then packets travel .
b/w client and server.

note:- processes on same host, when try to get connected to same server ,it would be given unique port number. all
connections must be unique.

q) how many types of sockets , java provide?
a) 3 types:-
1) connection oriented(TCP) :- implemented with Socket class.
2) connectionless(UDP) sockets use DatagramSocket class.
3) MulticastSocket class allows data to be sent to multiple recipients.

q) what is a thread?
a) it is also called light weight process. it consist of thread id,program counter,register set. it shares with other
threads belonging to same process code,data section and other o.s resources. traditional heavy weight process has single
thread of control. if a process has multiple threads,it can do more than 1 task at a time.

q) give an example of thread?
a) a word processor may have a thread for displaying graphics, another for reading keystrokes, third for performing
spelling and grammar check.they also play an important role in remote procedure calls(RPC).

note:- instead of process creation on web server to handle a client a thread is created to service request.


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