According to the Desktop P55C datasheet the CPU has a +/- 3.57% tolerance on the Vcc2 plane.
The base voltage is 2.8V and the actual range would be 2.70004V to 2.89996V.

The Icc2 power supply current is supposed to draw 6,5A at 2.9V and 233MHz and in the datasheet it's calculated ad 2.9V
Remember: The 17W power dissipation is the absolute maximum the CPU will draw. The worst case at 233MHz with 2.8V, but the typical, or average, active power of the 233MHz P55C is just 7.9W!

The 17W are calculated at 2.8V while the 6.5A are calculated at 2.9V.

Hope this helps a little bit 😀

SavantStrike wrote:

I'm a bit confused at the moment. I know Pentium MMX chips are VRE, but I'm at a loss as to what the proper voltage for the chip is. The back side of my 233 MMX says core voltage is 2.8V, but my motherboard only supplies 2.73V or 2.91V. Some of the material I've read shows that the current the chip draws is calculated at 2.9v, and not at 2.73. Furthermore, it appears the voltage range for the Pentium MMX is between 2.7 and 2.9 volts.

So does this chip run at 2.91V, or 2.73V? It makes a pretty big difference too as the motherboard I use has VRM's that can supply a maximum of 7A. With a TDP of 17W, that means the chip would draw ~5.8A at 2.91V and ~6.2A at 2.73V (alhough oddly enough the data I'm reading says 6.5A, but that can't be right). I'm not happy about that as the VRM's got too hot to touch with a Pentium 133 non mmx (3.4A). Admittedly, this is with no airflow, but I'm still concerned.

Additionally, I got my figures for TDP from this site. It's got all sorts of handy data for all kinds of chips. Amperage is provided, but the 2.73v amperage was not (but V= IR so no worries 😀 ).

I think you can run the MMX chip at both 2.73v and 2.91v, it shouldn't make much of a difference.
Basically, if your board officially supports your chip, then it's "supposed" to be safe to use them 😉
I know what you mean about the VRM heatsink getting very hot. If the design of your motherboards allows it, try mounting a heatsink that lets the extra airflow cool the VRM as well (or if you really want it hardcore, you could creatively mount another fan just to make sure the VRM receives better cooling).

I messed up saying V = IR before. I meant to say W = V X A. And since a good deal the energy consumed by a CPU goes straight to heat, then I just used TDP as a measure of total wattage. I'm a bit confused how at 2.9V the chip can draw 6.5A though, as for most of the other chips I looked at, the TDP is very much indicative of what the amperage will be. But to get 6.5A at 2.9V, it would have to have a TDP of 18.9W.

I'm concerned running this board at 2.73V as I'm pretty sure I could end up drawing close to the max the board can supply if I want to try and flog this thing and play some 3D titles on it (just for fun). I'll see how the VRM's run with some airflow on them. I intend to mod the front of the case this board goes in with a 120x38mm Panaflo which pumps out around 80CFM, so given the form factor and the location of the VRM's, they should run pretty cool. Even still though, running close to design limits is something I don't like doing. And it would get close, if the chip really does draw up to 6.5A at 2.91V, then it could 6.92A at 2.73V.

At the same time, 2.91V is the upper limit of the acceptable operating range of the chip, and by running in that range, CPU life may be shortened. Electromagnetic migration and all that jazz. Again though, the chip is going to be running very cool as it has a S370 heatsink on it and will also be in the path of the 120x38mm fan (yay for baby AT).

If only the board was designed to deliver say 7.5A. As it is I think it's probably a safer bet to keep the cpu voltage higher and the amperage on the motherboard lower?

Since MMX chips have a TDP of around 17W, your figure of 18.9W seems pretty close enough.
I'm not sure what practical value the amperage holds, other than whether a particular motherboard can handle it.

Iirc the heat produced by motherboards with the linear VRM thingy would increase if the voltage supplied to the CPU decreased, somewhat offsetting the benefit of reduced heat production by underclocking.

Tetrium wrote:

Since MMX chips have a TDP of around 17W, your figure of 18.9W seems pretty close enough.
I'm not sure what practical value the amperage holds, other than whether a particular motherboard can handle it.

Iirc the heat produced by motherboards with the linear VRM thingy would increase if the voltage supplied to the CPU decreased, somewhat offsetting the benefit of reduced heat production by underclocking.

That's the thing though, Intel's figure is 17W, but if they say 17W and 6.5A (and the voltage was 2.9V), then it's got to be 18.9W. I'd swear something is wrong with their datasheet. It won't matter much though as Mystery is right, the chip isn't going to come close to that most of the time.

IDK, I think I'll run the chip at 2.91V. I have a nice oversized heatsink for it, although I probably should have lapped it better. It's easier to keep the CPU cool than the VRM's.

So, thanks for the help all. 😀

Np 😉

Btw, it does depend on where you're getting your data from. I've tried doing calculations like those myself a number of years ago and found that in the end, there just isn't enough standardized data to get a comprehensive pattern.

Tetrium wrote:

Np 😉

Btw, it does depend on where you're getting your data from. I've tried doing calculations like those myself a number of years ago and found that in the end, there just isn't enough standardized data to get a comprehensive pattern.

Well, first I got it from the website I linked to in my first post, and then Mystery had data that backed the same findings up from Intel.

I'm looking at the Intel datasheet right now and the relevant data is on pages 31 and 32. Current is 6.5A as measured with the processor at 2.9V (page 31). TDP is 17W as measured with the processor at 2.8V (page 32).

Why the heck would they measure current at one voltage and TDP at another voltage?

At any rate, if it ran at 2.9V, TDP is in the 18 watts with some change territory according to a couple of the calculators floating around the internet. What I can't tell is if the amperage would remain constant, or if it would decrease.

SavantStrike wrote:

Why the heck would they measure current at one voltage and TDP at another voltage?

I really can't give you a sound explanation for the discrepancy shown in your data, other then that both values are probably 'measured' under different circumstances. I doubt the data is false, it's more likely the data is misleading for lack of a sound explanation.

I doubt any of the data is incorrect, as there doesn't seem any reason why a multimillion company would supply incorrect data to non-customers

Tetrium wrote:

SavantStrike wrote:

Why the heck would they measure current at one voltage and TDP at another voltage?

I really can't give you a sound explanation for the discrepancy shown in your data, other then that both values are probably 'measured' under different circumstances. I doubt the data is false, it's more likely the data is misleading for lack of a sound explanation.

I doubt any of the data is incorrect, as there doesn't seem any reason why a multimillion company would supply incorrect data to non-customers

It seems as though it's all in order, I just can't figure out why they did it the way they did, other than perhaps there are a lot of motherboards like mine with marginal VRM circuitry and perhaps the chip could draw say 7.1 or 7.2 amps at a lower voltage.

The 18 ish watts at 2.9V is also in line, as raising the voltage does raise the TDP. I'll agonize over the higher voltage and probably just snag a spare chip or two and not care about the chip. I'm more attached to the motherboard than anything 😀.

SavantStrike wrote:

I'll agonize over the higher voltage and probably just snag a spare chip or two and not care about the chip. I'm more attached to the motherboard than anything 😀.

That would be my thought 😀
The MMX chip is much more expendable then an AT SS7 motherboard!

Tetrium wrote:

SavantStrike wrote:

I'll agonize over the higher voltage and probably just snag a spare chip or two and not care about the chip. I'm more attached to the motherboard than anything 😀.

That would be my thought 😀
The MMX chip is much more expendable then an AT SS7 motherboard!

This is actually even harder to find. It's not SS7. It's a 430HX based board with proper tag ram. You wouldn't believe how many of them have crap tag ram, which defeats the entire purpose of the 430HX chipset. Even this one comes with crap tag ram, it's just that the COAST module has another tag chip on it and all is then well.

It's an irritating stunt that was pulled too. If the manufacturer isn't going to put in proper tag ram, then why not just make it a 430TX board.

SavantStrike wrote:

This is actually even harder to find. It's not SS7. It's a 430HX based board with proper tag ram. You wouldn't believe how many of them have crap tag ram, which defeats the entire purpose of the 430HX chipset. Even this one comes with crap tag ram, it's just that the COAST module has another tag chip on it and all is then well.

It's an irritating stunt that was pulled too. If the manufacturer isn't going to put in proper tag ram, then why not just make it a 430TX board.

Dunno...I just hope the ASUS P55T2P4 boards will cache correctly though. I know one of them works, even though one of those little SIMM tabs was broken. I'd need to salvage cache chips from somewhere though.

I wasn't aware that HX boards are becoming harder to find, last time I checked Ebay they were going for a LOT less then Socket 3 boards

Tetrium wrote:

SavantStrike wrote:

This is actually even harder to find. It's not SS7. It's a 430HX based board with proper tag ram. You wouldn't believe how many of them have crap tag ram, which defeats the entire purpose of the 430HX chipset. Even this one comes with crap tag ram, it's just that the COAST module has another tag chip on it and all is then well.

It's an irritating stunt that was pulled too. If the manufacturer isn't going to put in proper tag ram, then why not just make it a 430TX board.

Dunno...I just hope the ASUS P55T2P4 boards will cache correctly though. I know one of them works, even though one of those little SIMM tabs was broken. I'd need to salvage cache chips from somewhere though.

I wasn't aware that HX boards are becoming harder to find, last time I checked Ebay they were going for a LOT less then Socket 3 boards

They aren't hard to find at all. Don't go hoarding them yet 😜.

They're just hard to find in the right form factor. Originally I wanted a 430HX board in ATX. That was harder to find.

They're easy to find in Baby AT. It's just finding one that you can guarantee has the right tag chip on it, or finding one that you know you can upgrade that tag ram on adds a bit of complexity and once you settle on one then you don't want to spend another 30 minutes finding another.

SavantStrike wrote:

They aren't hard to find at all. Don't go hoarding them yet 😜.

They're just hard to find in the right form factor. Originally I wanted a 430HX board in ATX. That was harder to find.

They're easy to find in Baby AT. It's just finding one that you can guarantee has the right tag chip on it, or finding one that you know you can upgrade that tag ram on adds a bit of complexity and once you settle on one then you don't want to spend another 30 minutes finding another.

Lol!
Ah, I see now. Good thing I'm already stocked up well enough on HX boards already. The ASUS P55T2P4 apparently was a popular board here in The Netherlands 😁

SavantStrike wrote:

They aren't hard to find at all. Don't go hoarding them yet :P. […]
Show full quote

Tetrium wrote:

SavantStrike wrote:

This is actually even harder to find. It's not SS7. It's a 430HX based board with proper tag ram. You wouldn't believe how many of them have crap tag ram, which defeats the entire purpose of the 430HX chipset. Even this one comes with crap tag ram, it's just that the COAST module has another tag chip on it and all is then well.

It's an irritating stunt that was pulled too. If the manufacturer isn't going to put in proper tag ram, then why not just make it a 430TX board.

Dunno...I just hope the ASUS P55T2P4 boards will cache correctly though. I know one of them works, even though one of those little SIMM tabs was broken. I'd need to salvage cache chips from somewhere though.

I wasn't aware that HX boards are becoming harder to find, last time I checked Ebay they were going for a LOT less then Socket 3 boards

They aren't hard to find at all. Don't go hoarding them yet 😜.

They're just hard to find in the right form factor. Originally I wanted a 430HX board in ATX. That was harder to find.

They're easy to find in Baby AT. It's just finding one that you can guarantee has the right tag chip on it, or finding one that you know you can upgrade that tag ram on adds a bit of complexity and once you settle on one then you don't want to spend another 30 minutes finding another.

It's when things AREN'T hard to find to find that you want to start hoarding them. If you wait until they become hard to find you'll end paying more for them. 😜

sliderider wrote:

SavantStrike wrote:

They aren't hard to find at all. Don't go hoarding them yet :P. […]
Show full quote

Tetrium wrote:

Dunno...I just hope the ASUS P55T2P4 boards will cache correctly though. I know one of them works, even though one of those little SIMM tabs was broken. I'd need to salvage cache chips from somewhere though.

I wasn't aware that HX boards are becoming harder to find, last time I checked Ebay they were going for a LOT less then Socket 3 boards

They aren't hard to find at all. Don't go hoarding them yet 😜.

They're just hard to find in the right form factor. Originally I wanted a 430HX board in ATX. That was harder to find.

They're easy to find in Baby AT. It's just finding one that you can guarantee has the right tag chip on it, or finding one that you know you can upgrade that tag ram on adds a bit of complexity and once you settle on one then you don't want to spend another 30 minutes finding another.

It's when things AREN'T hard to find to find that you want to start hoarding them. If you wait until they become hard to find you'll end paying more for them. 😜

But by hoarding them, I make them hard for others to find 😜.

SavantStrike wrote:

sliderider wrote:

SavantStrike wrote:

They aren't hard to find at all. Don't go hoarding them yet 😜.

They're just hard to find in the right form factor. Originally I wanted a 430HX board in ATX. That was harder to find.

They're easy to find in Baby AT. It's just finding one that you can guarantee has the right tag chip on it, or finding one that you know you can upgrade that tag ram on adds a bit of complexity and once you settle on one then you don't want to spend another 30 minutes finding another.

It's when things AREN'T hard to find to find that you want to start hoarding them. If you wait until they become hard to find you'll end paying more for them. 😜

But by hoarding them, I make them hard for others to find 😜.

Exactly! Just try to find a Diamond Rendition Verite, you won't find them, as I already got all of them!!!11 😁

Tetrium wrote:

SavantStrike wrote:

sliderider wrote:

It's when things AREN'T hard to find to find that you want to start hoarding them. If you wait until they become hard to find you'll end paying more for them. 😜

But by hoarding them, I make them hard for others to find 😜.

Exactly! Just try to find a Diamond Rendition Verite, you won't find them, as I already got all of them!!!11 😁

I'm still floored you bought NINE 233 mmx chips (yeah that's right, I saw that on CPU World). 😜

All I can think is that you're running them at 3.3V or something 😜.

SavantStrike wrote:

Tetrium wrote:

SavantStrike wrote:

But by hoarding them, I make them hard for others to find 😜.

Exactly! Just try to find a Diamond Rendition Verite, you won't find them, as I already got all of them!!!11 😁

I'm still floored you bought NINE 233 mmx chips (yeah that's right, I saw that on CPU World). 😜

All I can think is that you're running them at 3.3V or something 😜.

Yup, fastest desktop MMX chip ever made...and they were how expensive?
That's right, they were dirt cheap!
Life long supply! 😁