Pegasos G4 Upgrade

[Dietmar]

I always wondered about CPU slot architecture, if you actually get the same performance out of it as if it were surface mounted.

It was a widely used design before x86  became multi GHz and FSB speed exploded, so apparently no inherent problems with a slot CPU. Anyway, the PPC does not leave much choice: the CPU does not have pins. It can only be soldered to the board (cost-effective but rendering the board non-upgradable) or be installed on a CPU card. That pretty much decides it for me.

[Dietmar]

only drawback of the Pegasos I design is... the DESIGN of the Pegasos

I have to admit I'm very impressed by your ability to diagnose systems you have not designed, out of your armchair, not even knowing what bplan's fix fixes. As to MAI's Arctica, it seems to work reasonably well in MAI's evaluation boards which should not surprise anybody. It also works well in designs derived from those boards. Big surprise. But it did not work well in the independendly designed Pegasos before fixes were added. There are at least two conclusions: Pegasos is poorly designed. Your conclusion. Or: the Arctica does not meet its specifications. I don't design boards (obviously) but, generally speaking, assume that boards are not designed by trial and error but based on the chips' specifications. If that is the case, the Arctica may very well be full of problems that just did not show up with MAI/Teron-derived boards. It will be interesting to see how the Marvell chipset works in a bplan design: it's better spec'ed and should require more design skills than an Arctica-based board.

[Dietmar]

> AFAIK, Slots tend to be more (electrically) noisy than sockets. This means you have to run the memory slower to keep it reliable.

On the purely logical level, this statement makes no sense: noisy it may be, whatever that is, but if the memory has to be slowed down or not would depend on the tolerance of the design for "noise".

On a purely empirical level, this statement obviously makes no sense, too: slot boards were the dominating design for a while and those boards did not run memory slower to keep it reliable (as far as I can remember).

[Dietmar]

What do you mean by "more design skills"?

Compared to the existing Pegasos, just about everything is higher spec'ed: PCI-X rather than PCI, the FSB will be faster (183 MHz?), the memory bus will be faster (and DDR vs SDR), etc. I was just assuming that faster components require more design skills.

[Dietmar]

Make a search on www.armada.ch and you will find their are other developers, independent of Mai, who produce marketable goods

On a purely logical level, that does not mean that the Arctica is not the culprit. It is perfectly possibly that it does not meet its specs and that the designers you are referring to have run into the same brick wall. Maybe they just had more money and redesigned their boards to meet Artica's bugs instead of having a rather visible  (and annoyingly expensive) kludge directly under MAI's chip? They would have ended up with the same result: a working mainboard.

[Dietmar]

>Ever wondered why Intel dropped those slot designs?

Maybe it's more interesting to ask why to start with a slot design? CPUs are flat. Going the extra mile and soldering a CPU to a vertically mounted card seems to defy reason. In the case of Intel, I recall problems with getting sufficient cache into the CPU. When that was fixed, they reverted back to cheaper sockets. In the case of Genesi, I suspect it is their inability to grow pins to the PPC, leaving them little choice: solder or slot. The latter obviously provides more flexibility.

[Dietmar]

> Imagine trying to mount 200g of aluminium to the side of a chip mounted in a slot - it's not going to work...

That puts the name of this passive "Eliminator" heatsink into a whole new perspective :-)

Eliminator 0.5kg heatsink

>One can solder a BGA to a PCB, and mount the PCB is a socket.

What would still speak for the slot design rather than an adaptor PCB is that it's easier to add the stuff needed in direct vincinity of the CPU (ie. L3 cache on the backside, the capacitors), while keeping the micro-atx form factor.

[Dietmar]

A BGA can still be mounted on a PCB and be attached to a mother board in a way other than linear contacts along one edge.

With two CPUs? With L3 cache on the backside? While keeping the micro-atx form factor? I find it hard to imagine any other design but a slot to offer so much flexibility (but I haven't seen the mainboards you refer to).