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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 | Time Aspects of Process

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Important time parameters of process Arrival Time(AT) Entry time of process into ready queue. Burst Time(BT) Amount time spend for execution of process in CPU. Completion Time(CT) Finishing time of execution of the process Waiting Time(WT) Amount of time spend by process for waiting CPU after arrival and before completion. Turn Around Time(TAT) Time gap between arrival and completion time of a process. Response Time(RT) The range of time between initial scheduling and entry/arrival time of process. I/O Time The time spend for completion of input output request. For an preemptive algorithm the the waiting time and burst time may be intermittent time slices(BT1/ WT1,BT2/ WT2...) of its over all burst time(BT)/waiting time(WT). RT = tX - AT CT - AT = BT + WT WT = TAT - BT | Previous | Next | Home |
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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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