# CPU Utilization Rate and Turnaround Time Calculation in Uni-programming

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## 10 Questions

### What is the impact of multiprogramming on the overall turnaround time of processes?

It shortens the overall turnaround time.

### Which assumption about IO operations is made in the scenario described?

IO operations can only occur after all CPU bursts are complete.

### What is the reason behind the shortening of the overall turnaround time in multiprogramming?

Processes execute concurrently, allowing for overlapping CPU and IO operations.

### In a scenario where one process is in a CPU burst and another is in an IO operation, what time is saved?

The duration of the IO operation.

### How does multiprogramming impact CPU utilization rate compared to uniprogramming?

CPU utilization rate increases in multiprogramming.

### What happens during an overlapped period of time in a multiprogramming scenario?

CPU and IO operations of different processes overlap.

Process A

### Why does the OS select one process in a CPU burst to use the CPU?

To prevent the CPU from idling.

### What is a benefit of having a multi-programming scenario?

Reduced overall turnaround time

Assumption #2

## Study Notes

### Uni-programming System

• In a uni-programming system, only one process is allowed to execute at a time, and the execution of the next process begins only after the previous one has completed.
• CPU utilization rate is the proportion of time the CPU is doing useful work, which is 25% of the time in this case.
• Overall turnaround time is the total time taken for all three processes to complete their execution, which is the sum of individual process's turnaround time.
• In the given example, the overall turnaround time is 4 + 12 + 16 = 32 ms.

### Characteristics of Processes

• Process A, B, and C have turnaround times of 4, 12, and 16 ms, respectively.
• Each process spends 25% of the time in CPU bursts and 75% in IO bursts.

### CPU Utilization Rate

• The CPU utilization rate is not affected by the order of execution of the three processes in a uni-programming system.
• The CPU utilization rate is 25% in this case, which is calculated by the total time the CPU is being used divided by the overall turnaround time.

### Multi-programming System

• In a multi-programming system, the OS can execute multiple processes at the same time, and the CPU utilization rate is improved.
• Assumptions in a multi-programming system include:
• Ignoring the time taken by the OS to do work in executing the processes.
• IO operations cannot happen in parallel.
• For each process, CPU burst must happen first.
• The OS will execute all processes at the same time, and when one process is doing IO operations, the OS will select another process in CPU burst to use the CPU.
• The overall turnaround time is shorter in a multi-programming system due to the overlapped period of time when one process is doing CPU and another is doing IO.

Calculate the CPU utilization rate and the overall turnaround time of three processes (A, B, and C) with specific characteristics when only one process is allowed to execute at a time (uni-programming). The processes have defined turn-around times, CPU burst and IO burst times.

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