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Theory of Computation | Symbols, Alphabets, Strings and Language

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Theory of computation or Automata theory mainly deals with abstract modeling of machines and computation. These models embody some of the important complex logical features we encounter, on dealing software as hardware. The following are the basic terminologies, which are frequently used in Theory of Computation Symbol The smallest building entity of Automata Theory( or Theory of Computation) is known as symbol. example: a, 2, i, B... Alphabet A set of symbols forms an alphabet. An alphabet is usually represented by Greek letter sigma( Σ ) example: Σ= { x, y} String A string is a sequence of symbols in a alphabet. example: 'xy' is a string derived from the alphabet Σ= { x, y} Language Collection of strings are called as a language. example: Let an alphabet Σ= { p, q, r} Then if a language L of set of a strings of length 2 over Σ can be represented as L = { pp, pq, pr, qp, qq, qr, rp, rq, rr } ...
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Operating Systems | Scheduling Algorithms: HRRN

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Highest Response Ratio Next(HRRN) Response ration of a process in ready state at a moment is the ratio of sum of service time (equal to burst time) required and waiting time till that moment to the burst time. Among available processes on ready state ,a process with highest response ratio get allocated to CPU by a scheduler with HRRN algorithm. If response ratios are equal next priority will for one which is arrived first and even that also similar then next is for onw with lowest process ID. Example: Calculate completion time, turn around time and waiting time for the following processes using non-preemptive HRRN algorithm? Process AT BT P1 0 4 P2 1 3 P3 1 1 P4 3 2 Answer: The sequences of allocation of process into CPU can be depicted as follows: TAT = CT - AT & WT = TAT - BT ...
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Operating Systems | Scheduling Algorithms : Round Robin

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Round Robin Features : Most popular algorithm of all Practically implementable Implementable with basic data structures like queue Extremely lesser starvation Optimum efficiency can be set by controlling time quantum The round robin algorithm will continuously switch between processes if a process in CPU (under execution) exceeds a time limit set by OS called time quantum . Flow Chart : Scheduler allocated process to for execution. CPU starts monitoring the execution time right after from allocation. If the process completes its execution before exceeding time quantum, OS forwards the process to termination state. else, the processes gets preempted once the time quantum limit exceeded and if the process finished at this moment, OS moves the process to termination state, else it moves to ready queue and iterates over the whole process listed above. Example : Consider the following table of processes and calculate completion time, turn around time and waiting tim...
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