I have a 2006 mac pro, if I upgrade memory can I update to OS X Maverick?

No. Your computer can't run Mavericks, and in all probability, won't be able to run Yosemite.

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Apple only supports the 2006 and 2007 models up to 10.7.5, which continue to run in 32-bit kernel mode.

There are some hacks you can install that load the 64-bit firmware into main RAM, but Apple does not support them and does not condone discussing them in detail here. They started out as hacks to run Mac OS X on unsupported hardware. These hacks are only appropriate for users who are developers, or think like developers. There is NO support from anyone.

One helper download provides an extension that boots up 64bit firmware on top of the built-in 32bit firmware, and can only be run on older Macs (not Hackintosh) -- so this is less repugnant. A search for the words, spelled out, (no numbers) may give you some help.

You should already put 4 to 8GB RAM and it cheap enough, $22 - 44

Then move the system onto SSD great performance boost

Upgrade to Lion

There are tools and sites to get it to boot Maverick if you have another Mac that can but it is a hack, a alternative unsupported boot loader.

Was just wondering about the same thing. This is my configuration:

Model Name: Mac Pro

Model Identifier: MacPro1,1

Processor Name: Dual-Core Intel Xeon

Processor Speed: 3 GHz

Number Of Processors: 2

Total Number Of Cores: 4

L2 Cache (per processor): 4 MB

Memory: 11 GB

Bus Speed: 1.33 GHz

And according to everything I've read, Lion's going to be the end of the road for a straight-up OS upgrade - is this correct?

Yes, but:

If you need a big speedup (quick and easy) the SSD Boot Drive The hatter mentioned is worth considering.

You can also (if you are handy) consider upgrading your processor chips to make yours into the equivalent of a 2007 model with dual quad processors.

I like the idea of the SSD Boot drive, will give that some serious consideration. Any recommendations for sourcing that? I got a piece of garbage memory recently for a Lenovo upgrade, ended up buying Crucial's. What's worked for you?

Unlike for memory, any SSD will work. You do not even need SATA III SSD since your older Mac does not support that speed but a SATA III will works fine too.

If you are in the USA then Amazon has what I have found to be best engineered and price on FBDIMMs, $23 for 2x2

And can't go wrong with Samsung EVO - forget 128GB when 250 is only $139 (or less) and sometimes the 1TB drops to $389 area.

You do have two ODD SATA ports (on logicboard) that are SATA II and bootable, or use an SSD Icy Dock to adapt to the drive bay $14 also on Amazon.

PCIe SSD cards are not bootable but some are fine for data use, scratch, Aperture, iPhoto etc or audio and those uses do benefit from SATA III 6G

Even Crucial can not work once in awhile, cost more, but good service. Then again, as soon as UPS picked up and entered a return into their system hours after pickup, they let me know I would see my credit/refund in 2-3 days, which is amazing (don't do that often and didn't realize it had gotten so good) so very happy using Amazon.

The SSD with 8GB RAM or more were cheap but also the best performance improvement in 8 years. And I tend to upgrade GPU and the rest on a two year cycle.