This is old. About a rumour of N64 that I heard.

[Urian]

A little bird told to me that the original specs that were shown to the developers were under NDA and that the specs were this:

CPU 105Mhz
RCP 70Mhz
400k pol/sec with all the effects on.

and the final specs:

CPU 93.75Mhz
RCP 62.5Mhz
150k pol/seg with all the effects on.

I have heard 2 stories about this change of specs.

The first said that the desing of the SGI processor failed and Nintendo changed it for an IBM CPU losing a lot of power because the RSX has a lot of registers and instruccionts that must be used with the original CPU to work.

The second said that the RCP is 1/4 of Reality Inmersion because it was designed for run in 320x240 and the RI in 640x480. With this cut combined to the lack of sound chip in the system the console loses a lot of polygonal performance.

Any of you can confirm this?

And if you cannot tell anything in a public forum my MSN is urian10041983@hotmail.com.

 

[Guden Oden]

Well, the first rumor isn't true because there isn't an IBM CPU in the N64; it's a MIPS chip (and fabbed by NEC IIRC). The second rumor isn't true because the RCP is a custom jobbie built for the N64 specifically. So in the end, neither of your rumors are true.

 

[akira888]

Actually, to be a bit on the pedantic side, it is an SGI CPU in the Nintendo 64. At the time MIPS Technologies was owned by Silicon Graphics and the semi-custom CPU and the graphics subsystem were developed IIRC concurrently. Later, SGI spun MIPS off into a separate unit focused on the embedded market, and they adopted Itanium as their flagship CPU. Which was a debatable decision in retrospect.

From what someone was told me vis-a-vis vertex transform performance on N64 you can trade off less precision for more speed, and early microcode libraries leaned too heavily on the precision side, which later microcodes fixed. But my memory is fuzzy so I could be thinking about something else entirely. I've never done N64 hobbyist coding in my life. But feel free to ask about PSX!

 

[Guden Oden]

Actually, to be a bit on the pedantic side, it is an SGI CPU in the Nintendo 64.

ACTUALLY, it IS a MIPS CPU. MIPS was owned by SGI, but that doesn't make it an SGI CPU. The N64 CPU wasn't even a custom chip, it was (or even is still probably) available to buy as a stand-alone chip with pretty much the exact technical specs as in the N64 (only thing that differed were clock speeds, with some variations of R4400i being faster/slower than in the N64). Possibly, pinout might have differed between the N64 CPU and the stand-alone version, but I somehow doubt it; total pin count of the PLCCs themselves were also identical.

From what someone was told me vis-a-vis vertex transform performance on N64 you can trade off less precision for more speed, and early microcode libraries leaned too heavily on the precision side

Yea, that's been confirmed by...uhhh...I don't recall, some N64 ex-dev who posts here more or less regularly. Might've been ERP?

 

[akira888]

Well, I did give a pedantry warning. But in those days SGI was by far MIPS largest customer, so it's sensible to say they were calling the shots on design. On the R4300, IIRC it's a R4000 series chip with only a 32 bit external bus whereas the mainline R4000s had 64 bit data bus widths. While it was developed initially for Nintendo, it was sold later in the open market.

Vis-a-vis precision/speed, I found an old ERP post that confirmed what the hobbyist coder told me, which gives it much more credibility now.

 

[ERP]

I've never had this confirmed from anyone that would "know" but,
There was a rumour that the original design had 2 RSP's (or an RSP with twice the performance) in it, but this happened VERY early in development. We were one of the first US 3rd party devs to have dev kits and if it happened it was well before we saw hardware.