Following the previous upgrades to my 2006 Mac Pro I finally decided to take the plunge and swap out the original dual core Xeon CPU’s for some quad core ones.  A matched pair of Xeon 5355’s came up on Ebay at a sensible price and from a reputable seller so I snapped them up.  The seller actually had four pairs for sale and they were sold pretty quickly so there is clearly still some demand for 5355’s.

There are a multitude of videos available on Youtube detailing the relatively simple procedure of removing the old Xeons and replacing them.  All you need are the new processors, some good thermal paste, a couple of Phillips screwdrivers and a 3mm Allen/Hex key which needs to ideally be at least 6″ long.  You’ll also need something to clean the old thermal paste off of the heat sinks, isopropyl alcohol is ideal, anything else risks leaving residue which will negatively impact on the heat transfer between CPU and heat sink.  Optional extras are a can of compressed air for cleaning out any dust build up and an anti-static wrist strap.

I won’t go into the full procedure here as others have already documented it well.  A couple of points I would make are firstly many who have performed the upgrade refer to issues removing the memory cage screws, I had no such problems but did use a small jeweller’s screwdriver which allowed vertical orientation and full purchase with the screw head.

Secondly, I was surprised by how thick the factory application of thermal compound was when I removed the heat sinks, I had expected a thin veneer but it was definitely thicker than that.  This rather threw me as to how much compound I should apply on re-installation.

In the end I decided to apply a thin line horizontally across the CPU’s with an additional smaller vertical line making a cross.  I didn’t spread out the compound but instead allowed the pressure of re-attaching the heat sink to flatten it out.

Reassembly was straightforward, I even managed to complete the whole operation without dropping one screw.  The machine promptly booted up and I ran Geekbench to assess what performance improvement the new Xeons were giving.

With the original Xeon 5150’s Geekbench would typical return a score in the low 5000’s.  With the 5355’s the score has leapt to 9456, a very useful improvement in performance bringing my 2006 Mac Pro within touching distance of a 2012 iMac Core i7.

The only thing left to do now is monitor the CPU temperatures for a while to ensure the thermal compound is working well.  There are a number of different apps out there that claim to give accurate read outs of the Pro’s thermal sensors, however in my experience they all seem to give different results.  I’ve therefore decided to trust the software that I’m familiar with, namely Marcel Bresink’s aptly named ‘Temperature Monitor”.

This is showing the cores running at an average of about 40°C under light load* which is around 30% higher than the previous processors. Considering there are twice as many cores and that the thermal compound has not broken in yet this seems pretty reasonable to me.  Also a considerable upswing in the ambient temperature that has coincided with the upgrade must be taken into account.

I decided to download SMC Fan Control and crank the systems fans up by a couple of hundred RPM just to be on the safe side, they are still whisper quiet.  There is one last issue that needed resolving, when you perform this upgrade and click on About This Mac you’re likely to get a processor unknown reading although System Report will show the correct number of cores.

There are a couple of solutions to this, you can try upgrading the 1,1 firmware to 2,1 using this utility.  Or you can do what I did which was download the CPU injector Kext from here (updated with new link, see original article here) and install it with a kext utility, I used Kext Helper b7 here (updated with new link.)

*After three months of running smoothly the CPU temperatures under light load are now averaging around 32°C so clearly the thermal compound has bedded in well and I’ve been able to leave the fans running at factory settings.  I recently installed Windows 7 and have been enjoying a number of games, the machine remains stable and reliable.

*More than 12 months have now passed since this upgrade and I’m pleased to report the machine is still running smoothly.  Despite very hot ambient temperatures here presently, the Mac Pro remains whisper quiet.

*Update (08 December 2013) Following John’s post in the comments section below I returned to find some of the links in the original post broken.  I have therefore hosted the CPU Injector Kext and the Kext Help B7 utility myself and updated the links.  The original article covering the CPU injector Kext can by found at the Internet Archive.  With regards to the machine itself it is still running perfectly.

*Update (19 December 2013) I’ve installed OS X Mavericks using the target disk mode method.  Running Geekbench again under Mavericks yields a result of 9841.

*Update (11 October 2014) Another reader has pointed out that the links in the original post are broken again.  I have therefore reolcated and hosted the CPU Injector Kext and the Kext Help B7 utility myself and updated the links.

*Update (7 May 2018) I have noticed that this post is still quite popular and I thought therefore that those reading it might be interested to know that this Mac Pro is still running without fault.

*Update (23 June 2020) This post remains popular, those reading it might be interested to know that this Mac Pro is still running without fault.