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Intel Lynnfield Core i5 750, Core i7 860 and Core i7 870 CPU review: bombarding the mid-range

by Tarinder Sandhu on 8 September 2009, 05:00 4.0

Tags: Core i5 750, Core i7 860, Core i7 870, Intel (NASDAQ:INTC)

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LGA1156 and LGA1366. What's the difference?

Lynnfield and Bloomfield. Core i7 and Core i7. Que pasa, hombre?

The question Intel's engineers face with cutting down existing Core i7 parts is which performance-enhancing features to leave out, to ensure the newer models don't quite compete on a clock-for-clock basis with the established chips.

Same architecture, really?


Lynnfield chip (courtesy of Intel)

Known by the codename Lynnfield and presented on an LGA1156 form factor - which means they won't work in present X58 chipset-based boards - the incumbent Bloomfield (LGA1366) architecture is kept intact, for the most part. All chips are based on a monolithic quad-core design, manufactured on a 45nm process, and ship with 1MB L2 and 8MB of shared L3 cache. Further similarities extend to the feature-set, which includes SSE4.2 support, Intel SpeedStep Technology and 64-bit operation. Hyperthreading, too, is present on all chips bar the entry-level Lynnfield.

Lynnfield, presented in a smaller CPU package, will share Bloomfield's 700m+ transistor-count, as much of the guts are the same. Indeed, the package is only smaller because of the lower pin-count; the silicon is the same, if not larger.

What's different?

DMI

From an architecture point of view, Lynnfield chips will interface with the system via a DMI (Direct Media Interface) conduit rather than QPI found on Bloomfield. QPI has greater bandwidth and provides processor-to-processor support in a multi-socketed system. Lynnfield is aimed squarely at the client market and the substituting of DMI for QPI should make little performance difference.

PCI-Express

Adding in a neat trick, Intel is plumbing 16 PCI-Express lanes - used primarily for graphics - right into the new chips, rather than have a separate bridge handle the duties. What this means is that the chips' supporting core-logic, P55, doesn't require an IOH bridge, as found on X58 boards.

Dual-channel memory

Current Bloomfield chips use a tri-channel memory-controller that provides excellent bandwidth. Our testing, however, has shown that the processors are relatively memory-agnostic, working almost as well in dual-channel mode - helped on, no doubt, by the large 8MB of L3 cache. Lynnfield drops the third memory channel and runs a regular dual-channel memory setup.

Intel, however, adds official DDR3-1,333 support for Lynnfield chips, up from DDR3-1,066 on most Bloomfields, helping bridge some of the pure bandwidth disadvantage.

Lower power-draw

We like the fact that Intel has dropped the power-draw of the Lynnfield chips from 130W to 95W, and we're adamant that low-power versions of the Core i5 750 and Core i7 860, pulling a maximum 82W, will be released shortly.

Enhanced Turbo Boost

The Turbo Boost feature has been enhanced for Lynnfield. The premise behind it is to ensure that compute power is kept to a maximum as long as it fits inside the chip's TDP.  Bloomfield chips can increase their frequency by one 'multiplier' (133MHz) if running all four cores, and by two for applications taking advantage of one or two cores. Lynnfield increases four-core load by two steps (266MHz), dual-core processing by four steps (533MHz) and single-core usage by five steps (666MHz). That's impressive overclocks considering the 95W TDP.

Evaluated on a clock-for-clock basis, Lynnfield chips lose a little speed, due to a lack of a third memory channel and QPI, but introduce a more-robust Turbo Boost feature that's inextricably allied to a lower power-draw.