[T42] DDR400 running at DDR333 speeds..

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azredwing · #1 Post by **azredwing** » Wed Aug 01, 2007 7:20 pm

Hey all,

I ran CPU-Z on my T42 and saw that the FSB is running around 400MHz, so I decided to get some DDR400. I put it in and.. it's still running at DDR333 speeds.

I did some reading on the boards before I decided to post and saw that this isn't unusual. Am I right in thinking that DDR400 is going to be reduced to DDR333 speeds? And if so, why would the FSB be running at 400MHz?

Thanks.

#2 Post by **Harryc** » Wed Aug 01, 2007 7:31 pm

It sounds like you are confusing the RAM bus speed with the CPU front side bus. The memory is PC2700 running at 333MHz. The CPU is a Mobile Pentium M which runs at 533 MT/s. Where you saw 400MHz I have no idea. Can you post a screenshot of what you saw? In fact if you could post screenshots of all the CPUZ screens it might give some clues. What processor do you have in that machine? What was the original RAM stick? If you saw anything running 400Mhz, is it possible that someone swapped a T40 or T41 base into the machine and it is running a 400Mhz Dothan or Banias?

http://www-307.ibm.com/pc/support/site. ... MIGR-57839

azredwing · #3 Post by **azredwing** » Wed Aug 01, 2007 7:53 pm

On the bottom left, you see "Rated FSB" around 400MHz.

Right now I put the old memory in there: 2 GB of PC2700. This screenshot is the same when either the PC2700 or the PC3200 is in the board.

#4 Post by **Harryc** » Wed Aug 01, 2007 8:15 pm

Right, the bottom left is your CPU core speed. That has nothing to do with the RAM speed, which is 166MHz, PC2700.

azredwing · #5 Post by **azredwing** » Wed Aug 01, 2007 8:17 pm

Harryc wrote:Right, the bottom left is your CPU core speed. That has nothing to do with the RAM speed, which is 166MHz, PC2700.

Core speed and FSB are not the same thing. The rated FSB is ~400MHz. Why would the FSB, which runs at 400MHz, not be able to run PC3200 at DDR400 speeds -- 400MHz?

#6 Post by **Harryc** » Wed Aug 01, 2007 8:53 pm

azredwing wrote: Core speed and FSB are not the same thing. The rated FSB is ~400MHz. Why would the FSB, which runs at 400MHz, not be able to run PC3200 at DDR400 speeds -- 400MHz?

I meant to say the bottom left is your CPU FSB speed. For some reason I was thinking you had a T43, but 400Mhz is correct for a T42 FSB. As far as the RAM question, with your chipset RAM speed is set up to be 2/3 of CPU FSB. As far as I know that is a chipset limitation which you will not beat with faster RAM. PC2700 is the correct RAM for your machine.

Melvyn · #7 Post by **Melvyn** » Wed Aug 01, 2007 11:14 pm

First: FSB speed isn't DDR spped.
Second: Your machine (your motherboard) support DDR333 (PC 2700), not DDR400 (PC4200).
Third: Your DDR will run at the slower rate from your dimms. If you mixed DDR333 with DDR400 it will run at 333 (even if your machine support DDR400 or not).

Well, only for general culture: DDR stands for "Double Data Rate".
A dimm named "DDR333" is in fact PC 2700. In reallity is not 333MHz. It's 166MHZ (doubled).
DDR400 stands for a dimm which runs at 200MHZ.
And so on.

By the way, FSB stand for Front Side Bus and it's not so related with your impressions. It says "400mhz". In reality it runs at 100mhz.

azredwing · #8 Post by **azredwing** » Wed Aug 01, 2007 11:24 pm

Fair enough, but if I *only* use DDR400 RAM, why would it clock down to DDR333?

I think the chipset explanation is the most likely..

Melvyn · #9 Post by **Melvyn** » Wed Aug 01, 2007 11:59 pm

azredwing wrote:Fair enough, but if I *only* use DDR400 RAM, why would it clock down to DDR333?

I think the chipset explanation is the most likely..

Your machine, your chipset, it's limited to DDR333. From your motherboard it can't "read" at more spped from your memory. It's hardware limited.

lilserenity · #10 Post by **lilserenity** » Thu Aug 02, 2007 2:29 am

Without wishing to duplicate what has already been excellent explained (quad pumped busses and double-data-rates aren't exactly that easy to explain!) the major reason your ThinkPad doesn't think "Hey I have faster RAM, let's let it stretch its legs and go full pelt" is that the RAM would start running faster than the rest of the system which is designed to communicate with the memory at a certain speed; in which case the RAM would be flinging information out too quick for the parts of the system to cope and so it would miss the cycle it is expect to respond on; and in actual fact slow things down or cause system instabillities.

The only way I can describe this is a club with everyone dancing to some music in perfect time, and then some drunkard comes in stumbling and falling over, before leaping into the air again and again like some lunatic before stumbling some more, it spoils things and it doesn't really work

The issue is that there is a lot of other logic besides the RAM and CPU which is only rated and set to work at 333MHz DDR rates; and one part of the system (a major part) that runs faster than it should will cause problems.

DDR is a clever idea that does what it says on the tin where it manages to squeeze two I/O ops into one clock cycle, so rather than just operating on the clock signal, it operates on both the rise of the clock signal and the fall of the clock signal; so the part is still working at 133/166/200 etc. MHz but by effectively doubling what it sends vs. a SDR part on the same clock speed, it effectively becomes the equivalent of 266/333/400MHz SDR part.

I hope I've got this right

At least that's my understanding of these things. Goodness knows how DDR2/3 figures into this, I just make websites; that's all

Melvyn · #11 Post by **Melvyn** » Thu Aug 02, 2007 10:41 am

Oh Vicky you're so clear, so sweet...

Are you single?

lilserenity wrote:The only way I can describe this is a club with everyone dancing to some music in perfect time, and then some drunkard comes in stumbling and falling over, before leaping into the air again and again like some lunatic before stumbling some more, it spoils things and it doesn't really work

SHoTTa35 · #12 Post by **SHoTTa35** » Thu Aug 02, 2007 11:35 am

Melvyn wrote:Oh Vicky you're so clear, so sweet...

Are you single?

lilserenity wrote:The only way I can describe this is a club with everyone dancing to some music in perfect time, and then some drunkard comes in stumbling and falling over, before leaping into the air again and again like some lunatic before stumbling some more, it spoils things and it doesn't really work

\

picking up girls on a forum? bad bad move!

Melvyn · #13 Post by **Melvyn** » Thu Aug 02, 2007 1:06 pm

SHoTTa35 wrote:picking up girls on a forum? bad bad move!

Well SHoTTa35, I'm not looking for girls, but this one: girl + thinkpadder + coder + geek + linux girl + writer...

That's sound like a ThinkPad with n-Core at 20GHZ, 128GB of Ram, 16GB of video, and plenty of Tera Bytes.

SHoTTa35 · #14 Post by **SHoTTa35** » Thu Aug 02, 2007 1:27 pm

well honestly i was thinking the same that you are, you were just braver than me to say it

My girlfriend now is basically jealous of my Thinkpad and threatens to throw it out the window almost daily. LOL

Melvyn · #15 Post by **Melvyn** » Thu Aug 02, 2007 1:33 pm

SHoTTa35 wrote:My girlfriend now is basically jealous of my Thinkpad and threatens to throw it out the window almost daily. LOL

You're lucky because is a ThinkPad and can hit the window without issues. A typical Dell or Toshiba can be broken by the glass

lilserenity · #16 Post by **lilserenity** » Fri Aug 03, 2007 2:14 am

My god I'm whipping up a storm here

I'm just glad my words are helpful. I am single for the record; but there again I think I'll probably keep it that way for now!

As for being compared to a ThinkPad with 128GB of RAM; lol!

Oh I'm not the lunatic on the dance floor for the record; that would waste precious drink bounding around like an idiot

[T42] DDR400 running at DDR333 speeds..

[T42] DDR400 running at DDR333 speeds..

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