Cfrgtkky

I want to make a larger width of the selected box between two columns.

begin{table}[H]

  centering

  begin{tabularx}{columnwidth}{@{}XXX@{}}

  toprule

  textbf{Parameter} & Description & Unit\

  toprule

textbf{Task} & Total number of task in the system & numeric count\

textbf{VM} & Total number of VM in the system & numeric count\

textbf{Time} & Average required time to complete a task & milisec\

textbf{Utilization} & Resource utilization & %\

textbf{VM's BW} & Bandwidth allocated for each VM & MB\

textbf{VM's CPU} & Number of CPU in a VM & Numeric Count\

textbf{Utilization Model} & CloudSim utilization model & Stochastic\

 bottomrule

  end{tabularx}

  caption{Difference performance metrics label{tab:difMetrics}}

 end{table}

The mismatch between the intercolumn spaces is due to the fact you're using X for columns that should be l.

You can increase the spacing between the second and third columns like it's done below, but it would be curing the symptoms rather than the disease.

In the bottom table, you see how to increase the intercolumn space for a single table (in the environment); if you want it global, set the desired width of tabcolsep in the preamble. Probably you won't need to even for the present table.

documentclass{article}

usepackage{tabularx,booktabs}



begin{document}



begin{table}[htp]

centering



begin{tabularx}{columnwidth}{@{}XX@{hspace{2em}}X@{}}

toprule

textbf{Parameter} & Description & Unit\

toprule

textbf{Task} & Total number of task in the system & numeric count\

textbf{VM} & Total number of VM in the system & numeric count\

textbf{Time} & Average required time to complete a task & milisec\

textbf{Utilization} & Resource utilization & %\

textbf{VM's BW} & Bandwidth allocated for each VM & MB\

textbf{VM's CPU} & Number of CPU in a VM & Numeric Count\

textbf{Utilization Model} & CloudSim utilization model & Stochastic\

bottomrule

end{tabularx}



caption{Difference performance metricslabel{tab:difMetrics}}



end{table}



begin{table}[htp]

centering



setlength{tabcolsep}{1em}

begin{tabularx}{columnwidth}{

  @{}

  >{bfseries}l

  X

  l

  @{}

}

toprule

Parameter & Description & Unit\

toprule

Task & Total number of task in the system & numeric count\

VM & Total number of VM in the system & numeric count\

Time & Average required time to complete a task & milisec\

Utilization & Resource utilization & %\

VM's BW & Bandwidth allocated for each VM & MB\

VM's CPU & Number of CPU in a VM & Numeric Count\

Utilization Model & CloudSim utilization model & Stochastic\

bottomrule

end{tabularx}



caption{Difference performance metrics}



end{table}



end{document}