The cube will run a 7450 or 7455 fine. Apple intentionally crippled the firmware for later CPUs like the 7447, 7457, and 7448. You can patch the firmware for these to work though, which is how the various aftermarket CPUs work in the Cube.
Yes, the VRM can be a limitation for running high power CPUs. There is plenty of info on this, as well as aftermarket VRMs.
Yes, at the same clock the 7450 is slower than the 7400. Check out barefeats for benchmarks of systems from that era, notably the 533MHz digital audio vs the 733MHz version.
real world speed test results for performance minded Macintosh users
barefeats.com
real world speed test results for performance minded Macintosh users
barefeats.com
Quite interesting. I was mainly interested in the fact that the 7450 had some advancements over the 7400/7410 which could make a couple things faster. (which could be better optimized for the 7450 if possible?)
And yes, the cache runs at full speed on the 7450 whereas it runs at half speed on the 7400/7410 chips, but the 7450 has effectively LESS cache than a 7400/7410 card. The pipeline appears to be longer (not sure by how much, but it was almost 2x longer if i recall correctly) which could cause instructions to take more time.
I also heard that some QS cards use the 7455... which was merely a revision of the 7450. Same transistor count, same manufacturing node, different scaling. Maybe it has something different internally that does not relate to the clock speed, but I am not sure.
My other concern is L3 cache.... which may or may not work. The failed AGP>QS experiment didn't detect any L3 cache whatsoever, and I am afraid the cube may not detect it either. To be fair, that card was pretty broken, even before I started modding it. Seems like these later dual G4s just have a fair share of issues. I even had a 1.25GHz dual MDD card just... fry itself upon starting up when NO mods were made. The chips oozed out a weird brown liquid in a very small quantity, and I called it quits from there. As with the experiment I did a year and a half ago, I will never forget that Curb Your Enthusiasm reply.
With all this in mind, I have thought of quite a complicated project. I might get some complaints in, but hey... I was born to modify hardware, especially old PowerPC macs that could have much better potential. I even got a 2005 eMac to run at 1.92GHz and it's still rock stable! Plan to put an SSD in and install z970's Sorbet Leopard.
...Or I might just end up slapping a dual 500MHz 7400 G4 in this thing. With a fan, of course. The computer works great and I even managed to put a Radeon 7500 from a QS2002 in here. Fancy having Quartz on a cube!
