We recently moved our website http://www.mspinc.com to a new server and it seems slower. Could a busy server (multiple sites hosted on it) cause long time to first byte?
Yes, but there are a lot of other tuning parameters that could also cause it (Database, APC cache, Apache configuration).
Do you think the Time to First Byte is slow?
Yep. Excruciatingly. It should be well under 1 second.
Good to know. Thanks.
When you say it should be under 1 second, so you mean per file or total?
Sorry, I mean for the base page itself - the first byte time from when the test started until the base page started to come back (which is the measured first byte time for the test) - this is including the DNS lookup and socket connect.
For individual requests for the static content the first byte times should be substantially lower than that and should basically just be the round trip time (usually under 100ms).
What do you think about the time to first byte for this internal page?
That’s not bad. What you want to do is compare the orange bar to the green bar. If they are exactly the same size then that’s as fast as you could EVER be. Having a green bar around twice the size of the orange bar is on the better end of what I usually see.
And hence the “A” for first byte time 
Great. I guess I’ll just work on the homepage then. This all got started when we went to a new host and our bounce rates jumped.
Why do some files not have an orange bar?
The orange bar is for the initial connection to a given host for each TCP socket (browser connection). Once a connection is open the browser can re-use it for multiple requests so it’s normal for most of the requests to not have the orange bar. If you scroll down to the connection view waterfall you can see how each of the connections is re-used.
In general, the orange bar should be the same size for all of the connections to a given host name.
What do you think would be the best course of action for diagnosing the long first byte time on the homepage?
It’s going to depend on the platform, skillset and if you are using a 3rd-party content management system (Wordpress, drupal, etc) or if it is all under your control.
Most of the back-end tuning and diagnostics is going to require a developer and/or a sysadmin who know how the app works and how the pieces are put together.
My favorite tool for getting visibility into the back-end is New Relic: http://newrelic.com/ but you can also get by by instrumenting things yourself.
I have large time to first byte for static content on IIS 7.5, it’s not site specific it’s slow for all sites on that server. Web.config setting runAllManagedModulesForAllRequests is set to false, and gzip is enabled for static content. How can I troubleshoot this problem ?
Here are the timings, time to first byte for fairly complex ASP.NET site is 368 ms, and for just grabing css file is 617 ms !! That time is different every time but still too much, not below 200 ms that seems way too much for such task.
Server has plenty free memory (in this moment more than 7 GB).