Operating Systems

Advantages of Drainage

There is no doubt that a drainage system will improve your crop yield. The implementation of a corrugated polyethylene pipe drainage system gives you more control over the moisture content of the soil than was ever thought possible. With Global Positioning Systems (GPS) not only can you check the overall condition of the soil, you can see how yielding patterns improve when moisture content is altered with a drainage system. Installing a drainage system has a number of impressive benefits. Control over the moisture content of the soil:

• Reduces the effect of droughts and excessive water from heavy rains or snow.
• Increases the temperature of the soil which loses its heat to excessive surface water.
• Improves aeration and the nitrogen content of the soil which results in earlier germination and better root development.
• Eliminates planting delays resulting in a longer growing season
• Removes toxic material and disease organisms
• Reduces soil erosion by creating better root systems

Greater Profitability

If you're looking for better productivity and a faster return on your investment, installing a tile drainage system comes out ahead of new machinery, land acquisition and new buildings. And it does it, convincingly. The profitability begins right from your first crop after installing drains.



Greater Productivity

According to Ontario's Crop Insurance Program, tile-drained farms increase yields from 22% to 42% compared to untiled land.

Improved Conditions for Earlier Planting and Extended Harvest Season

Abruce Tile drainage system will ensure you can be on the field for planting at the earliest possible date. Those wet fall days should not stop you from getting your crops off the fields.

Better Soil Moisture Conditions

With better soil moisture conditions, you can plant your whole field earlier and extend your harvest season. Why? Tile drainage reduces excess moisture where plants take root, encouraging deeper rooting.

Reduced Compaction

Improved soil conditions reduce compacting from fieldwork or harvest operations. A better air/moisture balance in the soil also contributes to better root growth and micro-organic health.

Drought Resistance

And with a properly drained field, your crops are more resistant to drought, because deeper roots are able to find and utilize moisture more efficiently.

Better Use of Inputs

Fertilizer is used more effectively on drained soils. A seedbed that has consistent and ideal moisture speeds germination and emergence. Herbicides applied to the soil adhere better to soil particles.

Energy Saver

Well-drained fields will also take less of your time and energy. You won't have to return to wet areas after they've dried out because you'll have uniform moisture across all of your tiled land.

Increased Land Value

One additional and compelling benefit of a tile drainage system? It's an assured way of increasing the value of your land whether you work the farm yourself or decide to sell.

A terminal server is a specialized computer which aggregates multiple communication channels together. Because these channels are bidirectional, two models emerge: Multiple entities connecting to a single resource, and a single entity connecting to multiple resources. Both of these models are widely used. Both physical and virtual resources can be provided through a terminal server: centralized computing can provide multiple users access to a remote virtual operating system. Access Providers often use terminal servers to terminate physical connections to their customers

To see the working of the terminal server visit

http://technet.microsoft.com/en-us/library/cc755399.aspx

Answer:

Terminal server as allows windows Small Business Server 2003 and windows XP to host multiple remote desktop session. Terminal service provides for application deploment in windows server 2003,windows server terminal services that client computer connect to a remote computer, remoter desktop connect from to type in run mstsc /span. windows server 2003 system family provides a client license management systme known as teminal server licesing.

Remote desktop connection by default installed in windows XP, remote desktop used to initiate a terminal services session from client side. To open remote desktop type mstsc in the runbox then enter.

Create a Terminal Services From client disk. We are creating client disk a) Click start point to programs then administartative and after that click Terminal Services client creator. b) Create installation disk in dialog box, click the version of the clients disk then ok. c) Insert the disk then ok ,you have now created a teminal services client disk.

Microsoft windows terminal services built into windows 2000 server and windows server 2003 and then windows xp remote desktop. using terminal services connect the internet will require that you open port 3389, used by the remote protocol and then check the firwall setting. and tcp connection is configured for the terminal server network to allwow users will be connect. To disable or enable the Remote desktop service on a windows xp or windows serve 2003 computer, perform the follwing steps :- 1) Click start and then contorl panal and then select the system. 2) And then click the Remote tab. 3) After that Remote desktop, unchecked the Allow users to connect remotely to this computer .

Real time means that correctness of result depends on both functional correctness and time that the result is delivered

* Soft real time

:- Utility degrades with distance from deadline

* Hard real time

:- System fails if deadline window is missed

* Firm real time

:- Result has no utility outside deadline window, but system can withstand a few missed results

Scheduling: FCFS [60]

* assume processes arrive in this order: P1, P2, P3 * nonpreemptive scheduling * average waiting time: (0+24+27)/3=17 ms PIDBurstP124P23P33 Gantt chart 0242730

* assume processes arrive in this order: P2, P3, P1 * average waiting time: (6+0+3)/3=3 ms

PIDBurstP23P33P124 Gantt chart 03630

* in general, FCFS average waiting time is not minimal * in general, better to process shortest jobs first

Scheduling: Round Robin (RR) [61]

* similar to FCFS, but preemption to switch between processes * time quantum (time slice) is a small unit of time (10 to 100 ms) * process is executed on the CPU for at most one time quantum * implemented by using the ready queue as a circular queue * head process gets the CPU * uses less than a time quantum IMPLIES gives up the CPU voluntarily * uses full time quantum IMPLIES timer will cause an interrupt * context switch will be executed * process will be put at the tail of queue

[III.B] Scheduling: RR [62]

* assume processes arrive in this order: P1, P2, P3 * preemptive scheduling * time quantum: 4 ms * P1 uses a full time quantum; P2, P3 use only a part of a quantum * P1 waits 0+6=6; P2 waits 4; P3 waits 7 * average waiting time: (6+4+7)/3=5.66 ms

PIDBurstP124P23P33 Gantt chart 047101418222630

* very large time quantum IMPLIES RR = FCFS * very small time quantum IMPLIES context switch is too much overhead * quantum approximately CPU burst IMPLIES better turnaround * rule of thumb: 80% should finish burst in 1 quantum

Scheduling: Shortest-Job-First (SJF) [63]

* assume the next burst time of each process is known * SJF selects process which has the shortest burst time * optimal algorithm because it has the shortest average waiting time * impossible to know in advance * OS knows the past burst times - make a prediction using an average * nonpreemptive * or preemptive: * shortest-remaining-time-first * interrupts running process if a new process enters the queue * new process must have shorter burst than remaining time

Scheduling: SJF [64]

* assume all processes arrive at the same time: P1, P2, P3, P4 * nonpreemptive scheduling * average waiting time: (3+16+9+0)/4=7 ms

PIDBurstP16P28P37P43 Gantt chart 0391624

* SJF is optimal: shortest average waiting time * but burst times are not known in advance * next_predicted burst time by (weighted) average of past burst times * * next_predict = last_observed + last_predict * next_predict = initialized value (usually 0) * next_predict = last_observed

SJF: Weighted Average Burst [65]

: : : recent and past history the same time 0 1 2 3 4 5 6 7 Burst ()

6 4 6 4 13 13 13 Guess () 10 8 6 6 5 9 11 12

Scheduling: SJF [66]

* assume processes arrive at 1 ms intervals: P1, P2, P3, P4 * preemptive scheduling: shortest-remaining-time-first* P1 waits 0+(10-1)=9; P2 waits 1-1=0 * P3 waits 17-2=15; P4 waits 5-3=2 * average waiting time: (9+0+15+2)/4=6.5 ms

PIDBurstArrivalP180P241P392P453 Gantt chart 015101726

* nonpremptive SJF: 7.75 ms

Scheduling: Priority (PRIO) [67]

* assume a priority is associated with each process * select highest priority process from the ready queue * let be the (predicted) next CPU burst of a process * SJF is a special case of priority scheduling * assume: high numbers IMPLY high priority * then priority is * assume: low numbers IMPLY high priority * then priority is * equal-priority processes are scheduled in FCFS order * PRIO can be preemptive or nonpreemptive * priorities can be defined internally* memory requirements, number of open files, burst times * priorities can be defined externally * user, department, company

Scheduling: PRIO [68]

* assume all processes arrive at the same time: P1, P2, P3, P4, P5 * nonpreemptive scheduling * high priority: low number * some OS use a high number!!! See VOS. * average waiting time is: (6+0+16+18+1)/5=8.2 ms

PIDBurstPriorityP1103P211P323P414P552 Gantt chart 0161618 19

* indefinite blocking (starvation): low priority process never runs * aging: low priorities increase with waiting time, will eventually run

VOS Scheduling: PRIO, FCFS, SJF [69]

for (i=1; i<=10; i++){ /* 10 CPU BURSTS */

for (j=1;j<=HOWLONG;j++) /* 1 CPU BURST */

pm_busywait(); /* PID1:long PID2:medium PID 3:short*/

pm_yield(); /* GO BACK TO READY QUEUE */

}

PRIOFCFSSJFPIDBurstpriority=fixedpriority=equalpriority=1/burst1long21low2medium3 high1medium3short1 low1high

* schedulers favor different PIDs * SUMMARY shows CPU burst (running) time for each PID * SUMMARY shows waiting time for each PID in ready queue * Gantt chart shows how long each PID is on the CPU * schedulers have different performance

VOS Scheduling: PRIO [70]

================================================================

FREE SUSPENDED READY RUNNING WAITING RECEIVING SLEEPING WRITING READ

PID time cnt time cnt time cnt time cnt time cnt time cnt time cnt time cnt ...

--- ---- --- ---- --- ---- --- ---- --- ---- --- ---- --- ---- --- ---- ---

0 0 1 0 0 72 2 17 3 0 0 0 0 0 0 0 0

1 29 2 1 1 25 11 34 11 0 0 0 0 0 0 0 0

2 64 2 0 1 1 11 24 11 0 0 0 0 0 0 0 0

3 16 2 1 1 58 11 14 11 0 0 0 0 0 0 0 0

4 89 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0

5 89 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0

6 89 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0

7 89 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0

8 89 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0

9 89 2 0 1 0 1 0 1 0 0 0 0 0 0 0 0

---- --- ---- --- ---- --- ---- --- ---- --- ---- --- ---- --- ---- ---

TOT 643 14 2 4 156 36 89 37 0 0 0 0 0 0 0 0

Utilization: 80.9 %Busy

Throughput : 2.0 Jobs/Min

Wait Time : 28.0 Sec/Job

Burst Time : 24.0 Sec/Job

VOS Scheduling: PRIO [71]

Scheduling Algorithm: PRIO

>>> SUMMARY (READY) <<< >>>>>>>>>>> SUMMARY (RUNNING) <<<<<<<<<<

PID TOT Wait Time TOT Burst Time / Cnt = Single Burst

=========

1 25 34 11 3.1

2 1 24 11 2.2

3 58 14 11 1.3

Sum Wait Time: 84 /3 Jobs Sum Burst Time: 72 /3 Jobs

Avg Wait Time: 28 Sec/Job Avg Burst Time: 24 Sec/Job

Longest Wait: 58(PID: 3) Longest Single Burst: 3.1(PID: 1)

Shortest Wait: 1(PID: 2) Shortest Single Burst: 1.3(PID: 3)

* other algorithms will have different average wait time

VOS Scheduling: PRIO [72]

Gantt chart of CPU Usage (Last Scheduler: PRIO)

------------------+-----------+---+-----+---+---+-----+---+--

PID |0 |2 |2 |2 |2 |2 |2 |2

------------------+-----------+---+-----+---+---+-----+---+--

time 9 15 17 20 22 24 27 29

--+-----+---+---+-+-----+-------+-----+-----+-------+-----+--

PID |2 |2 |2 |2|1 |1 |1 |1 |1 |1 |1

--+-----+---+---+-+-----+-------+-----+-----+-------+-----+--

time 31 34 36 3839 42 46 49 52 56 59

------+-----+-----+-------+-+---+-+---+-+-+---+-+---+-+------

PID |1 |1 |1 |1|3 |3|3 |3|3|3 |3|3 |3|3

------+-----+-----+-------+-+---+-+---+-+-+---+-+---+-+------

time 63 66 69 7374 7677 798081 8384 8687

* other algorithms will favor different PIDs

Mechanism (how) vs. Policy (what) [73]

mechanism * how to do something * implementation or function with parameters * used in many ways (by policies) * OS may be micro kernel - only basic mechanisms * policies are decided at the user level

policy * what or when to do something * set of rules * use mechanisms by setting parameters * important choices in the design of the OS * mechanisms should be separate from policies

Mechanism vs. Policy: Examples [74]

Timer(x sec) * Policy 1: if LOW_PRIORITY Timer(0.1) else Timer(1.0) * Policy 2: if LOW_PRIORITY Timer(0.1) else Timer(0.2)

Schedule(job) * Policy 1: Schedule(I/O Job A); Schedule(CPU Job B) * Policy 2: Schedule(CPU Job A); Schedule(I/O Job B)

Preempt(job) * Policy 1: if A.running greater than 0.1 sec then Preempt(Job A) * Policy 2: if A.running greater than 0.2 sec then Preempt(Job A)

Remove_From

Ready_Q(job) * Policy 1: Remove_Ready_Q(oldest job): FCFS * Policy 2: Remove_Ready_Q(highest priority job): PRIO * Policy 3: Remove_Ready_Q(shortest job): SJF