title: Excel: Can using external links improve performance?
body: <p>I'm wondering if there is a performance gain when using external links vs. opening a spreadsheet and copying cells (using VBA).</p>
  
  <p>I would imagine that Excel has to open the file just the same, but when I test using the following code, external linking comes out faster:</p>
  
  <pre><code>Dim t As Double
  Dim rng As Range
  
  For Each rng In shtId.Range("A1:A5")
      t = Now
      ThisWorkbook.Names("rngID").RefersToRange = rng
      ThisWorkbook.UpdateLink "H:\manualData.xlsx", xlExcelLinks
      Debug.Print "link: " &amp; Format(Now - t, "######.0000000")
  
      t = Now
      Workbooks.Open "H:\manualData.xlsx", readonly:=True
      ActiveWorkbook.Close False
      Debug.Print "open: " &amp; Format(Now - t, "######.0000000")
  Next
  
  
  Results:
  
  link: .0000116
  open: .0000231
  link: .0000116
  open: .0000347
  link: .0000000
  open: .0000347
  link: .0000000
  open: .0000347
  link: .0000000
  open: .0000347
  </code></pre>
  
  <p>The workbook has a range of cells with lookup formulas keyed on an ID field.  These formulas have external links.  To test it, I change the ID and force an update.  To test the file open approach, I just open and close the source file.</p>
  
  <p>I'm looking to speed up a process that's having an issue due to low bandwidth over the network.  I've already explored various options and would just like to understand if this is a valid one.  I searched on this topic and some people say external links could cause performance issues while some say otherwise.  I'd like to get a better idea of the mechanism behind external links so that I can understand what to expect when implemented.</p>
  
  <p>Any thoughts?</p>