Technical Difference Between Q9450 And X3350

It has been almost two weeks since the speculated shipment dates for the Yorkfield 45nm processors. But Q9450’s are still hard to spot. It briefly appeared on Newegg in the evening of March 25 but the supply was apparently very limited and barely lasted till the next morning. And of course, early adopters had to pay a hefty premium. As a result, quite a few people bought X3350 instead.

Many forum posts have suggested that Q9450 and X3350 were largely identical and had recommended buying the cheaper server version of the chip (X3350) instead of Q9450. But are they really identical as claimed by so many people? I decided to figure it out myself.

After some digging, I found the data sheet for both Q9XXX and X33XX on Intel’s web site. After comparing the two specifications, it became clear that while the majority characteristics of these two chips are identical, there are some differences never the less. Here are some of the highlights:

Pin differences:

The following are the pins that Q9450 has but not defined for X3350

  • DPRSTP# (Deep Sleep State to Deeper Sleep State transition when asserted)
  • DPSLP# (Sleep State to Deep Sleep State transition when asserted)
  • SLP# (Sleep State)

The  absence  the above three signals in X3350 is not a surprise at all since it is a server class CPU, which usually means 24×7 operation.

A few test pins are different as well:

On Q9450, according to Intel’s documentation on the placement of pull-up resistors, TESTHI10 pin cannot be grouped with other TESTHI pins. While on X3350, this limitation applies to not only TESTHI10, but TESTHI11 and TESTHI13 as well.

Other electrical differences:

ICC_VCCPLL ICC for PLL land — 260 mA
RON Buffer On Resistance 7.5 – 11 Ω (GTL+ Signal Group)
ICC_VCCPLL ICC for PLL land — 130 mA
RON Buffer On Resistance 7.49 – 9.16 Ω (GTL+ Signal Group)

So, it does seem that the two processors are largely compatible. However given the TEST pin pull-up register placement differences, it is possible that certain workstation motherboards’ (e.g. workstation bords not specifically stated supporting X3350) designs do not meet Intel’s guideline for X3350 and may result some stability issues.

The minor current requirement should not be an issue in my opion, but the missing SLEEP states pins in X3350 could result in some stability issues as well, since those pins are reserved in X3350 and reserved pins in general requires a static reference voltage or simply unconnected. But on a board build for workstations specifically, those pins may change states as the processor goes into and comes out of sleep state.

To summarize, I personally would not recommend putting a non-officially supported CPU in for reasons stated above. In the case of Q9450 and X3350 though, the differences are minute enough and from a technical stand point, it is possible that most motherboards that support Q9450 may also be compatible with X3350. Of course, even a motherboard is electronically compatible with X3350, we would still need the blessing of the BIOS. And since X3350 is officially unsupported, such blessing is totally at the mercy of each motherboard manufacturer and can not be guaranteed.

I guess I will stick with a Q9450. Hopefully there will be more in stock soon as the IDF starts next week.

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One Comment

  1. hi says:

    Both spec sheets have the same diagrams and other info for entering low power states. See section 6.

    Both processors show an extended halt power of 12W.

    Thanks for the links.

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