Operating System - Concepts
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777 |
1016 | Program - Process and States of Process
778 |Program Vs Process :
779 |Consider an example where you have to open the google 780 | chrome.
781 |what will happen -:
782 |-
783 |
- The CPU got triggered to open google chrome. 784 |
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786 |
- The CPU will look for chrome in the RAM 787 |
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789 |
- If it finds then show that if not then search in the hard-drive 790 |
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792 |
- In the hard drive it will find the program and make a copy of it which is called a process 793 |
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795 |
- And Hence, we can open two windows of chrome itself which are nothing but two process of chrome 796 | running that is two copies of chrome moved to RAM from harddisk 797 |
799 |
800 |States of a process :
801 |-
802 |
- New State : When the program is making the process 803 |
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805 |
- Ready State : Instance or process is generated and ready for the CPU to take action. 806 |
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808 |
- Running State : Process is running by the CPU 809 |
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811 |
- I/O State : Process is ready for some I/O. 812 |
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814 |
- Terminated State : Process has done execution and has been removed from the RAM. 815 |
817 |
818 |Degree of Multiprogramming
819 |820 |
821 |Maximum number of processes which are present inside 822 | our computer is called degree of multiprogramming.
823 |For example
824 |if XPLANE takes 1 GB of RAM per process and total free 825 | RAM in user space is 4 GB then the degree of multiprogramming is 4.
826 |827 |
828 |Types of Operating Systems
829 |Basic Terminologies :
830 |831 |
832 |-
833 |
- CPU efficiency : CPU efficiency is somewhat related that for how less time the CPU 834 | was not working, for example in 10 seconds, the CPU needed to be idle for 2 seconds and working for 835 | 8 seconds then that CPU is 80% efficient. 836 |
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838 |
- Parallel Processing : Parallel processing is a type of processing when the 839 | processes are executed by the CPU at the same time. For example, a mother is feeding her two 840 | children with both her hands, left for one children and right for other. 841 |
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843 |
- Concurrent Processing : Concurrent processing is a type of processing when the CPU 844 | is focusing on one process at one time , For example, mother uses only one hand to feed her two 845 | children, when one child is chewing she use the hand to feed the other child and vice-versa. 846 |
848 |
849 |Types of Operating Systems :
850 |851 |
852 |-
853 |
- Batch Operating Systems : Batch operating systems have two properties, they only
854 | have one CPU and they can only hold one process in their RAM on a time point, that means a process
855 | need to be terminated if you want to open another process.
They have Degree of 857 | Multiprogramming - 1
858 |-
859 |
- Disadvantages :
860 |
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861 |
- Very Low CPU efficiency : Consider an example where you are using
862 | batch operating system for typing your name.
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864 |
- You type something on Keyboard ( I/O process, CPU idle). 865 |
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867 |
- CPU understands that ( executing ) ( CPU running ) 868 |
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870 |
- Output on display ( CPU idle, I/O process ) 871 |
As you know that execution and 873 | I/O can't be done at the same time, you can see how many times CPU goes 874 | idle ( resting CPU , not working) and that make it super inefficient .
875 |876 |
877 |
878 |
880 | - Very Low CPU efficiency : Consider an example where you are using
862 | batch operating system for typing your name.
882 | - Disadvantages :
860 |
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884 |
- Multiprogramming Operating Systems : This types of systems are widely used in 885 | today, they have one CPU and they can store more than one process in RAM and that makes it cost 886 | effective as well as they provide average efficiency for use. They use concurrent processing. 888 |
890 |
891 |-
892 |
- Multiprocessing Operating System : This type of processing systems have more than
893 | one CPU and they can also handle one than one process in their RAM. Like you might have heard
894 | octacore CPU that actually means that there are 8 processors embedded in the CPU which can undergo
895 | the processes that actually means Multiprocessing OS.
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897 |
- The major disadvantage they bring to us is their high cost. 898 |
900 |
902 |
903 |Process Control Block and Attributes of a process : 904 |
905 |906 |
907 |Terminologies :
908 |-
909 |
- Active Entity and Passive Entity : When you load up a process then there are two 910 | thing in the hard - disk before going to the RAM, one is the part which would be pushed to the RAM 911 | while there would be other part which is the main program, always in the Hard-disk, this part is 912 | called the passive entity while the other part is called the active entity. 913 |
915 |
916 |Process Control Block :
917 |When the process is load up there is not only the copy 918 | of the program that is placed inside the RAM, in RAM their is a whole process control block or PCB which 919 | is placed.
920 |In a PCB there are 4 parts basically, Stack 921 | Memory, Heap Memory, Data Part and Program Part
922 |-
923 |
- Stack Memory : A stack memory stores all the functions of the program which will be 924 | executed at some point of time. 925 |
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927 |
- Heap Memory : Heap Memory stores all the things which are dynamically allocated, 928 | which means the allocation was not done on build-time but it was done on the runtime. 929 |
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931 |
- Data Part : The variables which are attached to a function will go with the 932 | functions in the stack memory there is no issue with that but the variable which are not associated 933 | with any functions like global variables and static variables, where will they go?, they will be 934 | stored in data part of the PCB. 935 |
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937 |
- Program-Part : This is where the program itself get stored. 938 |
For several processes there are several PCB's 940 | controlling the process environment.
941 |Process Attributes :
942 |943 |
944 |Scenario to be understood : So till now it 945 | has been made clear that how CPU works, it is nothing but a resource manager somehow managing the 946 | processes's PCBs, this work is somhow done by schedulers, a process is scheduled means that 947 | processor is currently executing that operation and a process is truncated that means the process is 948 | eliminated by for sometime. 949 | Now, there are various scheduling algorithms which we use for scheduling processes, like first come 950 | first serve or shortest job first algorithm, now to understand process attribute, let's take an 951 | example that a processor is using a shortest job first scheduling algorithm. 952 | Now take two processes, A and process B, A take 5 ns to execute while B takes 2 ns to execute, the 953 | scheduling algorithm used the algo and obviously picked up process B to implement, B has somewhat 100 954 | lines of code and 100 files to be read by B to be executed, imagine any game in your mind, now the user 955 | pushed another PCB of process C which takes only 1 ns to execute, now according to the algo B should not 956 | be executed first, now C is the top priority. 957 | Now, C would get what it deserve, the first priority, say B has been executed till line number 20 okay 958 | and read 10 files out of 100 and also has opened 5 files out of 10 ( maybe displayed (I/0)) understand 959 | it like you are playing CSGO and a gun is loaded but the player model is not loaded yet. 960 | So, B need to be forcefully stop now and something we should also think with our common sense, 20 lines 961 | of code has been already executed, when we will come back to execute process B after we execute C we 962 | will not load those 20 lines of code, that will be efficient, 10 files we have already read so we will 963 | not read them again, 5 files have already displayed, we will not display them again, we need everything 964 | to be effiecient na, why we will do the work that we have already did. 965 | So, we need to store some information about B that how much work has been done to B first by the CPU, so 966 | that when we come back to B after the execution of C we have a clear knowledge of what we have to do 967 | next and we won't repeat things and are super efficient. 968 | That's why we use process attributes, they are nothing but some attributes which help us to store 969 | the information about a particular process.970 |
971 |
972 |-
973 |
- Process ID : Process ID is assigned to every process to every process automatically 974 | so that it can be easily identified by the CPU. 975 |
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977 |
- Process Counters : Process counters gives us information that how much process has 978 | been executed, in our case that is line 20. 979 |
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981 |
- Process State : Truncated or Scheduled. 982 |
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984 |
- General Purpose Registers : Registers are also memory blocks like heaps and stack, 985 | so consider that till the 20th line has executed the program has stored some information, consider 986 | playing CSGO, the player has 20 gold coins, so now we are terminating B we need to store this 987 | information also somewhere, so we store such information in registers. 988 |
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990 |
- Priority : The priority of the process according to the scheduling algorithm . 991 |
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993 |
- List of open files : The list of files B have read till now so you don't have 994 | to read them again 995 |
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997 |
- List of open devices : List of open devices for the process, take example of 998 | headphone support while playing CSGO, the process must remember na that it has given headphone 999 | support already so don't need to give them or verify them back. 1000 |
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1002 |
- Protection : While C is executing, B also has something in the RAM, so it is 1003 | ensured that C do not mess up with the registers of B, this is reffered as protection. 1004 |
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1007 |1008 |
1009 |1010 |
1011 |1012 |
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