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Review: Intel Core i7-3820

by Tarinder Sandhu on 19 January 2012, 08:54 4.0

Tags: Intel (NASDAQ:INTC)

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Cheap as chips

Intel muscled into its own high-end desktop CPU territory when it launched the Sandy Bridge E (SNB-E) chips in November 2011. Expanding on the specifications of the excellent mainstream second-generation Core chips by throwing more cores, cache and memory bandwidth into the equation, SNB-E was always destined to be good.

But having performance hegemony at the high end means Intel dictates release schedules as it sees fit. There's no obvious pressure on the chip giant from AMD, the competition minnow, so the SNB-E roll-out is more calculated than rushed. And while we applaud the devastating speed achievable by the Core i7-3960X or 3930K CPUs, the need to purchase a new, expensive motherboard - X79 boards start at £170 - quad-channel memory and a £450-plus chip price combine to make Intel's speediest desktop platform also its most expensive.

Indeed, SNB-E's pricing juxtaposes with the comparative value offered by mainstream Core i5/i7 chips, where the capable Core i5-2500K, overclockable to near-5GHz, can be picked up for £150, with compatible LGA1155 motherboards on sale for significantly below £100.

Cheaper SNB-E

What SNB-E needs, therefore, is a cheaper chip that may tempt potential purchasers into opting for an X79-based platform; motherboard manufacturers would assuredly welcome such a move that'll stimulate sales. While not yet appearing on the firm's website, Intel has slipped in the four-core, eight-threaded Core i7-3820 LGA2011 chip, priced at a tantalising $286 (£250).

Unashamedly borrowing a table from the Core i7-3960X review, here's how the 3820 fits in.

Model number Cores / Threads Clock Speed
(GHz)
Max Turbo
(GHz)
IGP Process Cache Interface Memory channels TDP Turbo tech Socket Price
Intel Core i7-3960X 6/12 3.30 3.90 N/A 32nm
(Sandy Bridge-E)
1.5MB L2 15MB L3 DMI 2.0 Quad
DDR3-1,600
130W 2.0

LGA2011

X79

$999
Intel Core i7-3930K 6/12 3.20 3.80 N/A 32nm
(Sandy Bridge-E)
1.5MB L2 12MB L3 DMI 2.0 Quad
DDR3-1,600
130W 2.0

LGA2011

X79

$564
Intel Core i7-3820 4/8 3.60 3.90 N/A 32nm
(Sandy Bridge-E)
1MB L2
10MB L3
DMI 2.0 Quad
DDR3-1,600
130W 2.0

LGA2011

X79

$286
Intel Core i7-2700K 4/8 3.50 3.90 Intel HD 3000 32nm
(Sandy Bridge)
1MB L2
8MB L3
DMI 2.0 Dual
DDR3-1,333
95W 2.0

LGA1155

H, P, Z 6-series

$332
Intel Core i7-990X EE 6/12 3.46 3.73 N/A 32nm
(Westmere)
1.5MB L2
12MB L3
QPI Triple
DDR3-1,066
130W 1.0

LGA1366

X58

$999
Intel Core i7-970 6/12 3.20 3.46 N/A 32nm
(Westmere)
1.5MB L2
12MB L3
QPI Triple
DDR3-1,066
130W 1.0

LGA1366

X58

$583
Intel Core i7-950 4/8 3.06 3.33 N/A 45nm
(Bloomfield)
1MB L2
8MB L3
QPI Triple
DDR3-1,066
130W 1.0

LGA1366

X58

$294

What you're looking at is three generations of Intel CPUs. The first three entries all belong to SNB-E, the Core i7-2700K calls SNB home, while the bottom trio highlight what's best about the previous high-end desktop generation.

The same, but not the same

The Core i7-3820 is both the same and different from its SNB-E siblings. It uses the same LGA2011 form factor and slots right into any X79 board. There's no on-board video, it's specified with a 130W TDP, and communicates with the IO via a DMI interface.

But the differences are what make it stand out, and the first obvious pointer that this is a cheaper derivative rests with fewer cores/threads. Dropping down from the 6/12 setup of Core i7-3960X/3930K, the baby LGA2011 chip runs standard four-core, eight-thread processing. And understanding just how Intel arranges cores and caches, L2, which is 256KB per core, drops down to 1MB and L3 to 10MB (it's roughly set at 2.5MB per core, though it is shared amongst cores).

Fewer cores and less cache spell lower performance. Intel ameliorates some of the damage by clocking the chip in at 3.60GHz, which is higher than both six-core parts, though overall Turbo Boost speed is a 3960X-matching 3.90GHz. Really, the default clock is kind of irrelevant on a chip that Turbos so effectively, and Intel is making the 3820 look better than it perhaps is: the top-line duo both Turbo by 300MHz when under all-core load. In fact, the following table fleshes it out.

Model number/cores active Native speed One core Two cores Three cores Four cores Five cores Six cores
Intel Core i7-3960X 3.30GHz 3.90GHz 3.90GHz 3.70GHz 3.70GHz 3.60GHz 3.60GHz
Intel Core i7-3930K 3.20GHz 3.80GHz 3.80GHz 3.60GHz 3.60GHz 3.50GHz 3.50GHz
Intel Core i7-3820 3.60GHz 3.90GHz 3.80GHz 3.80GHz 3.70GHz - -
Intel Core i7-2600K 3.40GHz 3.80GHz 3.70GHz 3.60GHz 3.50GHz - -

You see, under load - one to six cores - the 3820 is pretty much the same speed as other high-end chips: the default clock is semi-meaningless.