AnandTech: Apple Makes the Switch: iMac G5 vs. iMac Core Duo

The Search for Universal Binaries

All of the applications that we've looked at thus far are Universal binaries, meaning that they are compiled to work on both PowerPC and x86 architectures. And although the number of Universal applications is quite large, there are still quite a few that are missing. The entire Microsoft Office suite, all of Adobe's products, and even Apple's professional application line have yet to be made available as Universal binaries. All have been scheduled and committed, but we're still at least another month away from seeing their debut.

Apple has done a tremendous job of making sure that non-Universal binaries do run on their new Intel based Macs, thanks to a binary translation program called Rosetta. Apple has been extremely quiet about the specifics of Rosetta, in my opinion, because it is a temporary solution that doesn't perform very well and they would rather that everyone forget it exists and port to Universal binaries immediately than rely on it as a crutch. The basic gist of Rosetta is this: when a non-Universal application runs its PowerPC assembly code, it is handed off to Rosetta, which then translates it into another form, optimizes it and then generates its own x86 code. The code is also cached along the way so that frequently used code blocks run quicker, since they don't have to be re-translated.

If you're familiar with compilers, this very much sounds like a real time compiler, except that you are going from low level assembly code to low level assembly code instead of a high level programming language to the latter. And although the process works, it is primarily to ensure functionality and wreaks havoc on performance.

You can tell if an application is Universal or not by looking at its info, the Kind: field will be listed as "Application (Universal)".

The other side effect to a Rosetta-style binary translation is that the amount of memory that you need goes up, sometimes significantly. Let's look at an example. First, let's take a Universal application, in this case iPhoto, and look at its memory footprint:

	iMac G5 1.9GHz	iMac Core Duo 1.83GHz
iPhoto Memory Size (at Open)	20.48MB	21.24MB

On the iMac G5, the application, with no photos in its database, takes up 20.48MB of memory. On the Intel based iMac, iPhoto '06 occupies 21.24MB. We've already seen that the Intel based Macs do take up a little more memory when running the same applications as the PowerPC based Macs, so the differences here are expected.

Now, let's take a look at a non-Universal application, Microsoft Word, that has to be executed using Rosetta:

Rosetta Performance Comparison	iMac G5 1.9GHz	iMac Core Duo 1.83GHz
MS Word Memory Size (at Open)	40.03MB	64.43MB
MS Word # of Threads (at Open)	2	3

At startup, with no open documents, Rosetta increases the memory footprint of MS Word from 40MB to just over 64MB - an increase of over 60%!

Remember the PDF that we generated in our Pages benchmark earlier? Instead of outputting it to a PDF, I exported it to MS Word and opened it on the two machines. I timed how long it took to open the 116-page document, but first. let's look at how much memory MS Word is occupying:

Rosetta Performance Comparison	iMac G5 1.9GHz	iMac Core Duo 1.83GHz
MS Word Memory Size (116 page Document Open)	75.75MB	218.79MB
MS Word # of Threads (116 page Document Open)	4	5

The memory footprint of MS Word has gone absolutely insane, growing from "only" 60% greater than the native application on the G5 to just under 3x the size. With the document open, the Intel based iMac had 218.79MB of its 512MB of memory being used by MS Word and Rosetta, compared to 75.78MB on the G5. I stressed earlier that 512MB isn't enough once you start to seriously use iLife/iWork applications. Now it's worth amending that to include anything that requires Rosetta to run.

So, how long did it take to open the Word document? Approximately 69% longer, thanks to the necessary binary translation during the process. Since Rosetta operates in its own thread, I checked to see if having a dual core processor sped things up at all. Unfortunately, the gain is basically nothing.

Rosetta Performance Comparison	iMac G5 1.9GHz	iMac Core Duo 1.83GHz	iMac Core Solo 1.83GHz
MS Word Document Open	27.1 seconds	45.7 seconds	47.9 seconds
MS Word Document Convert to HTML	36 seconds	114 seconds*

I eventually mustered up the courage to do the unthinkable: convert the open Word document to HTML. On the iMac G5, this process took a healthy 36 seconds; on the Core Duo based iMac running Rosetta, the process took 114 seconds and then crashed, leaving me without my HTML file. No matter what I did, I could not get the process to complete without crashing.

I turned to one more test of performance under Rosetta; this time, to see how Rosetta impacted graphics operations as well as some more CPU bound tasks. Cinebench 2003 has yet to be made Universal, and as a scripted benchmark, it's very easy to generate and compare data that it produces. I used the unoptimized (non-G5) version for both platforms to keep things as equal as possible. The results are below (scores are in Cinebench 2003's own units, higher numbers are better):

Cinebench 2003 Rosetta Performance Comparison	iMac G5 1.9GHz	iMac Core Duo 1.83GHz	iMac Core Solo 1.83GHz
Rendering-1CPU	203	76	75
Rendering-2CPU		143
C4D Shading	246	103	101
OpenGL Software Lighting	634	182	185
OpenGL Hardware Lighting	1336	506	504

Once again, the inclusion of a second core doesn't really seem to speed up the translation process at all, with the Core Duo and Core Solo posting very similar scores. The actual performance is absolutely abysmal, not to mention the serious performance hit when looking at the OpenGL tests. In the OpenGL Software Lighting test, the Core Duo running the benchmark using Rosetta can't even perform at 1/3 the level of the G5.