Feedback and HRRN Scheduling Algorithms?

These are examples from William Stallings Operating Systems Internal and Principles Design (7th ed). Below are the process arrival times and the service times:

HRRN:

I understand A and B but then according to what C is chosen before others and then why D is in the end I don't understand...

Feedback with q = 2

I read on a source that is a priority version of Round Robin and on our script it says another version of short response next algorithm with q. I mixed everything on this one and cant really find a correct logic. Most interesting why is there a block greater than 2? Final block of B.

I would be glad if you can explain the answers.

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In the HRRN question, the process B executes from 4-7 ms. Since process C arrived at 4ms, it has to wait 3ms. Similarly process D, arrived at 6ms and it has to wait for 1ms.

According HRRN, ratio for C = 1 + 3/4 = 1.75 ratio for D = 1 + 1/5 = 1.2 , therefore process C executes from 7-11ms.

Now, D has to wait for 4ms more till C completes. Similarly E waits for 3ms.

Ratio for D = 1 + (4+1)/5 = 2 Ratio for E = 1 + 3/2 = 2.5

Therefore E executes next and D gets executed finally. Hope this clarifies. I have no idea about problem 2.

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