Intel's Core i7/Core i5 Lynnfield Processors
Nehalem’s new architecture shatters performance records
Last November, Intel shook up the CPU landscape with the introduction of their first Core i7 processors based on their then new next-generation Nehalem microarchitecture.
Nehalem brought with it a number of firsts for Intel. It was the first Intel processor to ship with an integrated memory controller -- previously this function was found on the North Bridge of the system chipset. By moving the memory controller from the chipset directly onto the processor itself, memory latency is dramatically reduced, thus improving performance. Intel actually one-upped AMD by outfitting the first Nehalem CPUs with a triple (rather than dual) channel memory controller.
Nehalem was also Intel's first processor to feature an L3 cache. 8MB of L3 cache is shared amongst all four processing cores. This last level cache stores data that the processor may need to use later, saving time as the CPU doesn’t have to tap into slower system memory.
Intel also introduced Turbo Mode with Nehalem. One lesson both Intel and AMD have learned the hard way is despite their work over the years with game developers, only a small percentage of games on the market today take advantage of more than two processing cores. In these cases, the other cores are essentially wasted.
With both AMD and Intel moving from two, to four, and next year, six processing cores, there’s very real potential that many of these additional cores will sit idling completely untapped by the software.
In these cases, Nehalem uses Turbo Mode to provide an instant performance boost. With Turbo Mode, the CPU can automatically shut down the cores that aren’t being used and overclock the core(s) that are being taxed. A built-in power control unit (PCU) watches the processing cores for aspects such as CPU utilization and temperature. If it detects that only one core is being used, it shuts off the other three cores and can bump up the speed of the one active core by up to 266MHz; so the one active core on a 2.67GHz Core i7-920 for example is clocked up to 2.93GHz. If the PCU detects that the core's power usage, current, or temps are too high at that level, it will automatically drop the active core down to just one speed bump (+133MHz), knocking you down to 2.80GHz.
We’ll be discussing Turbo Mode in much more depth later in this review.
Phenom II upper left, followed by Core i7 Lynnfield and Core i7 Bloomfield bottom
Bloomfield (left) Lynnfield (right)
Nehalem was also Intel’s first native quad-core CPU. Previously Intel merely slapped two dual-core processors together onto the same package, linked by the front-side bus (FSB). This native design improves communication between the four cores.
The final significant first Intel introduced with Nehalem is its Quick Path Interconnect (QPI), which replaced the FSB. QPI is a high-speed, point-to-point interconnect that provides connections between processors in multi-processor server systems and also links the CPU to the North Bridge (IOH chip) of the system chipset. Each QPI link boasts up to 6.4 Gigatransfers/second (one link is the equivalent of 12.8GB/sec of bandwidth), since it’s bi-directional, QPI effectively delivers 25.6GB of total bandwidth. In comparison, the latest Penryn Core 2 Quad processors relied on a 1333MHz FSB which provided up to 10.7GB/sec of peak bandwidth.
Intel incorporated a number of other additions and new features into Nehalem, including better prediction of branch instructions, SSE 4.2, and the return of Hyper-Threading, but for the sake of space, we’re going to suggest you flip back to our Nehalem preview article
for more info on the rest of the CPU’s features. The bottom line is that thanks to its new architecture, Nehalem was able to exceed all our expectations when it came to performance. The CPU was universally hailed as being the world’s best processor by media outlets across the globe.
Nehalem goes mainstream
Intel’s first Core i7 Nehalem CPUs relied on their high-end Bloomfield core. From the get-go, Bloomfield was intended for use in the fastest, most expensive high-end PCs. Intel refers to Bloomfield as the processor for “extreme gaming and enthusiast platforms”.
These flagship processors relied on pricey motherboards based on Intel’s X58 chipset and supported triple-channel memory (you could actually run the processor in single or dual-channel memory mode, but this reduced performance). At launch X58 motherboards sold for over $300, and triple-channel memory kits would set you back over $120: that’s well over $400 before you even factor in the cost of the processor!
Fortunately prices on X58 motherboards have come down significantly in the past 9 months, you can now find motherboards and triple-channel memory kits for about half of what you would’ve paid when Core i7 launched last November. These lower prices have helped boost Bloomfield’s adoption rate among gamers and enthusiasts significantly, but it’s still out of reach for the mainstream consumer who may not want to shell out over $1,000 for a decent Core i7 PC based on the Bloomfield/X58 platform.
For this user, Intel has concocted their Lynnfield core with P55 chipset.
Like Bloomfield, Lynnfield is based on Intel’s Nehalem architecture, only it’s been tweaked to make the CPU+platform more affordable for the mainstream market. Instead of Bloomfield’s triple-channel memory controller, Intel removes one of the memory controllers in Lynnfield, knocking it down to a dual-channel design. As a result, you only need 2 sticks of memory instead of 3 for the best performance.
At the platform level, the P55 chipset relies on a single chip, instead of the traditional North Bridge/South Bridge (2-chip) design of X58. For motherboard manufacturers, an expensive 8-layer PCB with six DIMM slots for memory is no longer needed for your high-end mobo (the cheapest X58 motherboards sometimes rely on 6-layer PCBs), a 6-layer PCB is all that’s required with just 4 DIMM slots (4-layer PCB if you’re willing to forego SLI/CrossFire).
Those are just a couple of the changes between Lynnfield and Bloomfield though. Read on for more details…