RCS is patch based, the most recent version is kept in clear text and the previous version is stored as a reverse patch and so on back to the first version.  So getting the most recent version could be fast (it isn&#x27;t) but the farther back you go in history the more time it takes.  And branches are even worse, you have to patch backwards to the branch point and then forwards to the tip of the branch.<p>SCCS is a &quot;weave&quot;.  The time to get the tip is the same as the time to get the first version or any version.  The file format looks like<p><pre><code>  ^AI 1
  this is the first line in the first version.
  ^AE 1
</code></pre>
That&#x27;s &quot;insert in version 1&quot; data &quot;end of insert for version one&quot;.<p>Now lets say you added another line in version 2:<p><pre><code>  ^AI 1
  this is the first line in the first version.
  ^AE 1
  ^AI 2
  this is the line that was added in the second version
  ^AE 2
</code></pre>
So how do you get a particular version?  You build up the set of versions that are in that version.  In version 1, that&#x27;s just &quot;1&quot;, in version 2, that&#x27;s &quot;1, 2&quot;.  So if you wanted to get version 1 you sweep through the file and print anything that&#x27;s in your set.  So you print the first line, get to the ^AI 2 and look to see if that&#x27;s in your set, it isn&#x27;t, so you skip until you get to the ^AE 2.<p>So any version is the same time.  And that time is fast, the largest file in our source base is slib.c, 18K lines, checks out in 20 milliseconds.