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NVIDIA nForce 790i and Intel X48 Chipsets

Transition to DDR3, 1600 MHz FSB support, fully-fledged PCI-E 2.0.

June 23, 2008

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As was promised by NVIDIA representatives, motherboards on nForce 790i chipsets have appeared in stores in Q1 2008. That's right, "chipsets", although the company had promised only one chipset (but these chipsets naturally have only marketing differences). These solutions offer expected functionality: we already wrote about the most obvious changes to be introduced into the new chipsets in our review of the nForce 700i. However, both nForce 790i SLI chipsets differ noticeably from nForce 780i SLI and nForce 750i SLI. So we can say that they form the nForce 700i family, instead of regarding the new chipsets as replacements to older products (even though we had all reasons to believe that).

Another today's contender, Intel X48, is a typical Intel product: if a new generation of processors from this company is rolled out in the market, the company provides large-scale support for them - chipsets for all price segments and preferences. But if changes are made only to the top CPU segment, only a top chipset is launched, which differs from its predecessor only in minor mandatory details. The typical example is i925XE launched in addition to i925X: the new solution added only 1066 MHz FSB to the list of features supported by the previous product. Formally, the X48 belongs to a new generation of chipsets. But it does not have many features in common with the Eaglelake family, including the fact that the X48 will use the old ICH9 Southbridge instead of ICH10 (in future P/G45).

NVIDIA nForce 790i SLI and Ultra SLI

Let's sum up nForce 780i/750i SLI drawbacks and changes in the market since the nForce 700i, which require an adequate response. What concerns the drawbacks, we can recall its strange support for PCI Express 2.0 - it's implemented in an additional chip connected to the chipset with an insufficiently wide bus. Besides, nForce 700i is rather hot, but we cannot expect significant improvements here: chipset functionality hasn't been reduced, and this generation hasn't been upgraded to a new fabrication process. Besides, it does not always solve the problem.

As far as objective changes are concerned, we can mention only dropping prices for DDR3 memory (especially if we consider price correlations, not prices per se). DDR3 modules are still significantly more expensive than their DDR2 counterparts, but in this case both Intel and NVIDIA stake on the new memory standard. Thus, both nForce 790i SLI chipsets (they differ only in EPP2 support, and the Ultra chipset officially supports higher memory frequencies) offer the following characteristics:

NVIDIA nForce 790i Ultra SLI features
  • Support for all Intel Celeron 400, Pentium Dual-Core, and Core 2 processors; FSB clock rate can officially reach 1600 MHz; there is also official support for Intel processors manufactured by the 45-nm fabrication process (Wolfdale and Yorkfield)
  • Dual-channel DDR3-800/1066/1333 memory controller, up to four DIMM modules with the total size of up to 8 GB (without ECC), nForce 790i Ultra SLI supports SLI-Ready memory (with EPP 2.0)
  • Bidirectional HyperTransport bus (1 GHz, 16 bit in each direction) to connect chipset bridges
  • Three PCIEx16 graphics interfaces (two of them are based on the Northbridge, the third interface is based on the Southbridge) supporting 3-way SLI (x16+x16+x16), PCI-E ports on the Northbridge support PCI Express 2.0 mode (doubled throughput)
  • PCI Express x8 interface on the Southbridge
  • 4 x PCI Express x1 on the Southbridge
  • Up to five PCI devices
  • Up to six Serial ATA ports for six SATA300 devices (SATA-II, the second generation of the standard) supporting NCQ, TCQ, and Hot-plug
  • SATA RAID 0, 1, 0+1, and 5
  • Up to two ATA133 devices (one channel)
  • 2 x MAC controllers for 10/100/1000 Mbps network (Gigabit Ethernet) supporting such functions as unloading processor when processing TCP/IP traffic, traffic shaping, balancing the load, channel teaming and duplexing
  • Up to ten USB 2.0 devices
  • High Definition Audio support
NVIDIA nForce 790i Ultra SLI Northbridge

So, the new pair of chipsets feature the same Southbridge as in nForce 780i (and in nForce 680i). But their Northbridge is different.

NVIDIA nForce 790i Ultra SLI Southbridge is also used as an independent Northbridge

First of all, full support for Intel Penryn processors (45 nm) is confirmed. The list of supported products now includes models with the 1600 MHz bus (at the time this article was written, there was only one such processor - QX9770). Indeed, we acknowledge that QX9770 is fully supported by nForce 790i Ultra SLI motherboards.

Let's make a little digression. Many users are surprised to see "third-party" chipsets (in this case it's NVIDIA with the nForce 680i) having certain problems with the latest Intel processors (in this case - 45-nm models), although they were said to have full support for future processors. The fact is, only two companies compete in the profitable Intel chipset market: Intel and NVIDIA (we are not interested in the segment of budget solutions in this case). They compete by all undercover rules - backhanding, traps, and all that. For example, Intel came up with XMP extension of the SPD specifications for DDR3 memory modules. JEDEC is going to approve it, as Intel is quite influential in these circles - it's apparently done to spite NVIDIA's counterpart (EPP). Both companies have their trump cards: NVIDIA offers exclusive SLI support, Intel - traditionally promises support for the latest processors and new FSB parameters (it has been so since the old times and other competitors involved). So there is nothing surprising about it.

Secondly, PCI Express 2.0 has been finally brought to shape. Now both PCIEx16 interfaces (PCI-E 2.0) are based on the Northbridge without additional controllers. Moreover, PCI Express controller in the chipset can arrange data transfers directly between two PCI-E devices or send data from a processor right to all PCI-E devices at once. That is nForce 790i solves the problem of insufficient interface bandwidth for graphics cards (we actually noticed this insufficiency in practice only in special tests and solely in specific modes) and gets an advantage over other solutions in the market. To complete the picture, Northbridge can organize PCI-E interfaces as 2xPCIEx16 (PCI-E 2.0) or 4xPCIEx8 (PCI-E 2.0). As before, 3-way SLI uses the third PCIEx16 interface (PCI-E 1.0) in the Southbridge.

Memory controller is probably the most noticeable update in the nForce 790i. NVIDIA does not use a hybrid modification that supports both DDR2 and DDR3 (like in Intel 3x chipsets), the company switched from using DDR2 in nForce 780i and nForce 750i right to DDR3. It's difficult to distinguish oneself in this support, because the standards are dictated by JEDEC. By the way, maximum DDR3 speed (1600 MHz) was approved by this committee long ago, but JEDEC does not certify memory modules operating at this frequency yet. So officially you will need memory modules with EPP 2.0 if you want memory faster than DDR3-1333 (in case of Intel X48, you'll need XMP). The only difference between nForce 790i SLI and nForce 790i Ultra SLI has to do with their memory controllers: the former is limited to DDR3-1333 only, while the latter can work with SLI-Ready memory, including higher frequencies. By the way, NVIDIA chipsets can clock memory and FSB independently, allowing to use practically any combinations of their frequencies.

It's too early to describe the new SPD extension - EPP 2.0, which NVIDIA offered for DDR3. We are waiting for corresponding modules. In brief, it's an open standard (like EPP 1.0), actually an interpretation of EPP [1.0] for DDR3. This standard also implies several profiles for memory modules, they specify an extended set of memory timings and voltage. It must be noted that the system reads possible frequencies and timings at the first startup from SPD (at least well-written BIOS should do it). That is the system is guaranteed to start up and let a user choose a profile with increased frequencies/reduced timings/or both from EPP/2.

What concerns heat dissipation of the new chipsets, there are no significant changes versus nForce 780i, we've already mentioned it. Yep, a single hot bridge has disappeared. But its functionality has been moved into the chipset, which also has to support higher FSB and memory frequencies. So it will be hotter in any case. However, NVIDIA traditionally does not publish TDP values for their chipsets. Judging by the cooling system on the reference motherboard and our tests, nForce 790i remains one of the hottest (if not the hottest) products in its class. Besides, NVIDIA designs motherboards on its chipsets for enthusiasts (including overclockers), so cooling requires a serious approach.

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Page 2: Intel X48 Express

Page 3: Performance tests

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