title: virtual memory on compute nodes in a grid
body: <p>When I run a job on a node, using PBS, and I get finally in the job report: </p>
  
  <pre><code>resources_used.mem=1616024kb
  resources_used.vmem=2350176kb
  resources_used.walltime=00:06:32
  </code></pre>
  
  <p>What does the virtual memory really means? I don't think there is a hard drive connected to each node.</p>
  
  <p>Which kind of memory should I take into account when I try to increase the size of the problem, such that I don't hit the 16GB capacity of the node memory, the normal memory (mem) or the virtual memory (vmem) ? 
  Thanks</p>