Correction (15 September, 2009 @ 6:15 PM EST): The original run of this article indicated that the Lynnfield’s onboard PCIe controller depended upon the system’s bclock generator for its frequency. This is incorrect and has been redacted. All Lynnfield CPUs use an independent clock generator for the PCIe controller with a nominal frequency of 100MHz. Raising the bclock on a Lynnfield system will not push the PCI Express bus out of spec.
Original story follows:
Right on schedule, Intel has launched new Core i5 and Core i7 processors based on the LGA1156 Lynnfield core. Arriving in three flavors, are the new chips enough to unseat AMD’s price/performance crown? How do they stack up to the existing Bloomfield Core i7s? How are they different? Are they worth buying? We wanted to answer these questions ahead of our official Core i7 860 review which is coming soon.
First off, we wanted to drop all the current Core i5 and Core i7 parts in a table to show you their official specifications.
Next, we want to make some terminology very clear so as to avoid confusion going forward:
Bloomfield: This is the codename for the desktop Nehalem-based processors which launched last year. They use the LGA1366 socket, they are sold exclusively with Core i7 900 series branding, and are paired exclusively with the X58 chipset. The current roster of Bloomfield chips includes: Core i7 920, Core i7 950, and Core i7 975 XE.
Lynnfield: This is the codename for the desktop Nehalem-based processors which launch today. They use the LGA1156 socket, they are sold with Core i5 700 and Core i7 800 series branding, and are paired exclusively with the P55 chipset. The current roster of Lynnfield chips includes: Core i5 750, Core i7 860, and Core i7 870.
Now we’ll answer the million-dollar question…
How is Lynnfield different from Bloomfield?
First and foremost, Lynnfield chip is a value-conscious part. This does not mean that the two architectures won’t trade blows here and there, but it is important to know that Lynnfield is a Bloomfield that has been simplified in five big ways.
Out with QPI, in with DMI
QPI, or QuickPath Interconnect, is a new system bus architecture developed specifically for the Bloomfield-based Core i7 models. In its simplest form on a single-CPU system, QPI creates a high-speed 25.6GB/s link between the CPU and the X58 chipset.
The X58 chipset is then directly connected to the PCI Express bus, and uses a slower 2GB/s DMI link to connect to the ICH10(R) southbridge.
Lynnfield does not use an external QPI link, however. Instead, Lynnfield is launching with the P55 chipset, which condenses the north- and southbridge into a single chip called the PCH, or Platform Controller Hub. The PCH is connected directly to the CPU via that slower 2GB/s DMI link, and the PCI Express controller has been migrated onto the CPU.
QPI isn’t entirely removed, however, as it is still used internally on Lynnfield CPUs to connect the PCI Express controller to the CPU cores.
While dumping the northbridge/CPU QPI lanes in favor of internal QPI lanes won’t mean diddly for your average user, it could sway the opinion of high-end gamers:
- Tri- or Quad-SLI/Crossfire configurations are not practical on the P55. There is not enough PCIe bandwidth to reliably run them.
- SLI/CF+Physics configurations are not possible on the P55.
- SLI or CrossFire configurations are forced into two x8 PCIe lanes on P55, instead of 2 x16 lanes as with X58.
While the difference between 2×8 and 2×16 is immaterial at pedestrian resolutions like 1680×1050, 2×16 can be up to 7% faster at SLI/CF-friendly resolutions like 1920×1200 or 2560×1600. Seven percent is an admittedly small number, but we know that enthusiasts looking at CrossFire/SLI configurations are expecting the best.
On the opposite side of the coin, moving the PCI Express controller to the CPU die eliminates the latency penalty of going out across the northbridge to talk to the GPU. This is a major perk for users who intend to use a single graphics card:
- Lynnfield systems are absolutely faster than Core 2 Quad systems with a single GPU.
- The latency reduction means single-GPU Lynnfield systems with a higher CPU frequency than single-GPU Bloomfield systems will usually offer better gaming performance.
- The latency reduction translates to a direct performance advantage over Phenom II X4 systems: Clock for clock, the new Lynnfield CPUs are much faster than Phenom II.
Changing the memory controller
The Bloomfield’s second biggest change over prior Intel chips was the implementation of a tri-channel memory controller. This swanky tri-channel controller offers Bloomfield Core i7 Extreme chips three channels of up to DDR3-1600, while vanilla Bloomfield Core i7s are limited to three channels DDR3-1066.
Lynnfield, on the other hand, defaults to two memory channels of DDR3-1333 and slightly increases memory latency. These changes make for an exchange of blows with no clear winner, just as we saw with GPUs:
- Core i7 Extreme Edition Bloomfields offer significantly superior memory bandwidth to the Lynnfield.
- Regular Core i7 Bloomfields offer moderately superior bandwidth to the Lynnfield.
- Core i7 800-series Lynnfields also happen to support the 12x memory multiplier to enable DDR3-1600 support; this puts Lynnfield and Bloomfield neck and neck if a user knows his/her way around the BIOS.
- Core i5 700-series Lynnfields are stuck at DDR3-1333, which makes them the least favorable choice for anyone with memory-intensive applications.
The Bloomfield’s overclockability is owed to four multipliers all based off a 133MHz base clock (BLCK):
- CPU Frequency: BCLK * CPU Multiplier
- QPI (System Bus) Frequency: BCLK * QPI Multiplier
- Uncore (L3 Cache, Memory Controller) Frequency: BCLK * Uncore Multiplier
- DRAM Frequency: BCLK * Memory Multiplier
All four multipliers are completely independent, but there are two minor restrictions: The Uncore multiplier should be at least twice that of the memory multiplier, and the QPI bandwidth should not exceed 8GT/s. Aside from these small hang-ups, most X58 boards happily exceed a 200MHz BCLK, push 4GHz+ on the CPU (200*20), and hum along at DDR3-2000 (200*10).
The new Lynnfield, on the other hand, locks a whole slew of multipliers, which makes it slightly more difficult to overclock than the Bloomfield.
- CPU Frequency: BCLK * CPU Multiplier (LOCKED)
- Uncore (L3 Cache, Memory Controller & PCIe) Frequency: BCLK * Uncore Multiplier
- Core i7 800-series: 133*18 (LOCKED)
- Core i5 700-series: 133*16 (LOCKED)
- DRAM Frequency: BCLK * Memory Multiplier
These changes mean that the only way to overclock a system is by adjusting the BCLK until the system achieves the desired CPU frequency. From there, the memory multiplier can be adjusted to compensate for the rise in BCLK, but that’s it.
Don’t let that restriction fool you, though. Lynnfields are easily eclipsing 4000 and 4100MHz in testing, with DDR3 speeds fast approaching DDR3-2133. This is Bloomfield territory, so Lynnfield isn’t exactly crippled–it’s just more difficult.
A new socket
A CPU interfaces with the rest of the system via the pins on the bottom of the chip. Each pin provides voltage or carries data to other parts of the system. This means that drastic changes to the architecture of a CPU must be matched with drastic changes to the pinout of the processor.
Case in point, removing a memory channel calls for a reduction in pin count. The CPU no longer needs the pins that serve as a data channel for that third channel. Moving the PCI Express controller onto the CPU increases the number of needed pins. The processor must now have enough pins to accommodate the signaling requirements two x8 PCIe lanes.
The net result of these changes makes for Lynnfield’s new Socket H, better known as LGA1156. These new LGA1156 processors are not compatible with today’s crop of X58 motherboards, which is why the chips have launched with the P55 partner chipset.
Turbo Mode was a feature that debuted with the Core i7 that allows the processor to dynamically overclock itself if the CPU is operating within safe temperature parameters. Bloomfield Core i7s implement this feature by raising the chip’s multiplier by 1x or 2x, depending on the load demanded of the chip.
Lynnfield, on the other hand, is considerably more aggressive with Turbo Mode, and that is one of the biggest reasons why it is so damn competitive with the Bloomfield. Lynnfield more than doubles the range of Turbo Mode multipliers from 2-5x, which means the new chips might run up to 667MHz faster than their default frequencies. That’s pretty damn impressive if you ask us.
What about pricing?
Now that you know the ins and outs of what makes Lynnfield different from its big brother, let’s take a look at the real meat’n'potatoes of the launch: Pricing.
One of the biggest criticisms leveled at the Core i7 was that its price increase was not commensurate with the performance increase it offered over the Core 2 Quad. Furthermore, aggressive clock scaling from the boys in green meant that the Phenom II X4 965 put the price/performance crown squarely on AMD’s head.
Has Lynnfield done anything to change that? You bet.
On average, the lowly Core i5 750 turns in 8-20% better performance than the Phenom II X4 965 for $40.00 less. The price/performance win is clear in this comparison. Restricting our net to the Core i7s, the new Core i7 860 is clear price/performance champ for anyone looking to buy into the Core-series platform.
All of these chips are available immediately, and in volume, which means you can go out and buy one right now if you so choose.
The Lynnfield’s Achilles Heel
Westmere is coming. Westmere is the 32nm successor to today’s Bloomfield CPUs, and it will debut exclusively for the LGA1366 socket. Not only do Westmere chips offer six physical cores to today’s four, it will run colder, faster, and overclock better than any Nehalem we have talked about today.
Users enticed by tantalizing price/performance offers made by the Core i5 must answer an essential question: Are you really interested in opting out of more, cooler, faster cores?
That’s the big question, and it’s not for us to decide. Enthusiasts will almost certainly see the merits of buying into LGA1366, because they know that past die shrinks like Conroe to Penryn made impressive thermal and performance gains. More traditional users may not care, because they’ll own the system well into 2011, and by then both AMD and Intel will have new architectures in the form of Bulldozer and Sandy Bridge, respectively.
All that said, knowing that LGA1156 was born with limited upgrade options is a bit sobering, and it’s a big point of annoyance with us. Offering users a platform with little to no future is not taken kindly, and we were similarly critical of AMD when it did the same thing with Socket 754.
Making sense of it all
There is no clear answer for users looking to buy into Nehalem today. The upper echelons of Lynnfield completely cannibalize any value the Core i7 920 once had, which means Bloomfield’s barrier entry has really been raised to the $569.99 price tag of the Core i7 950.
At the same time, the promise of Westmere’s year-end launch makes a compelling argument for the 920. We do not believe the i7 920 is long for this world, which means it might be a great idea to prepare for Westmere by buying into LGA1366 while it’s less than $500 for a good board and a chip. Wait too long and that price tag may float towards $800 if the 950 becomes the low-end model in the Bloomfield family.
Running on the assumption that the Core i7 950 will soon serve as the lowest model in the Bloomfield family, you really only have four choices:
- Buy the Core i7 920 and an X58 motherboard right now to prepare for Westmere on the cheap, knowing that a Lynnfield system would have been faster
- Buy into Core i7 950+X58 for performance that exceeds Lynnfield, at the expense of a hefty increase in price over a Lynnfield solution.
- Maximize your price/performance by purchasing a Core i5 750 and a P55, knowing that you’ve beaten Core 2 Quads and Phenom II X4s, but fallen short of all other Core i-series products.
- Buy a Core i7 860+P55 for respectable savings and price/performance in the short term, at the expense of significant future upgrades.
Only you have the answer to that, but we hope we’ve made it a little easier to get there. For more answers and a slate of benchmarks, keep your dial tuned to Icrontic for our upcoming shootout between Bloomfield, Lynnfield and the Phenom II X4.