Utilization or U – Utilization of any system is defined as the Ratio of Busy Time to Total Time of Observation. Utilization is a ratio that generally refers to how busy or free the resources within a given system are. Utilization can also be used to refer to how busy or free are components within a given system instead of the system as a whole.
The following equations are used to describe Utilization:
- U = Bt / T …………………………. [ Bt = Busy Time, T = Total Observed Time Interval ]
The above equation describes utilization as the ratio of Busy Time to Total Observed Time.
Example: Let’s assume we are viewing a system for a period of 180 seconds during which it remains busy for 100 seconds.
- The Utilization of the system is calculated as follows:
- We know : U = Bt / T …………………………. [ Bt = Busy Time, T = Total Observed Time Interval ]
- Utilization (U) = 100/180 = 0.55
The Utilization thus for this system is 0.55.
In addition to the equation above Utilization can be described as:
- U = X * St …………………………. [ X = Throughput, St = Service Time ]
The above equation describes Utilization as the product of Throughput and Service Time. As mentioned earlier the above equation can be applied to either the system as a whole or at a resource level within a given system.
Example: Let’s assume we are viewing a system for a period of 180 seconds during which it remains busy for 100 seconds. The Service Time for a transaction is 2s. The throughput of the system is calculated as follows:
- U = X * St
- X = U / St = 0.55 / 2 = 0.275 Transactions/Sec
The equation provided below is very similar to the previous equation but with one subtle difference i.e. the addition of Average Number of Servers (of CPU’s in our case).
- Uavg = [ X * St ] / M …………….. [ Uavg = Average Utilization, X = Throughput, St = Service Time, M = Average Number of Servers ]
On a system with multiple servers (CPU’s) the average utilization is obtained by dividing the overall system utilization by the total number of servers (CPU’s) present.
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