Test by Bikram | Operating Systems | Test 2 | Question: 7

Question

A computer system has $6$ tape drives with n process competing for them. Each process may need up-to $2$ tape drives. The maximum value of n from which the system is guaranteed to be deadlock free is:

• A. $2$
• B. $3$
• C. $4$
• D. $1$

Answer 1

Suppose at any instance, all 4 processes are holding 1 tape drive each as follows
       Hold   Need   Available
P1      1       1         2
P2      1       1
P3      1       1
P4      1       1
$$\begin{array}{|c|c|c|} \hline & \text{Hold} & \text{Need} & \text{Available} \\ \hline P1 & 1 & 1 & 2  \\ \hline P2 & 1 & 1 &  \\ \hline P3 & 1 & 1 & \\ \hline P4 & 1 & 1 &\\ \hline  \end{array}$$
The two tape drives can be allocated to P1, which will finish execution and gives its drives back to available pool, so that the other processes will get access to tapes. Any execution sequence will lead to safe state here. The system with 4 processes ensures dead-lock free environment .

Comments

if 5 would be in options .would it b correct to mark it as answer?

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yes,if 5 is in option then 5 should be the answer

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The question should be modified something like this... "... the max value of n among the following..."

Because if you ask for max value (in general) (i.e. the maximum value n can have), then answer is 5 and none of the option matches.