Intel Core i7 Nehalem processor - 9 November 2008

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Intel Core i7 Nehalem processor

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This month, Intel moves on from the Core microarchitecture to the
next generation of processors for mobile, desktop and servers,
codenamed Nehalem and officially named the Core i7 family.

We've spent a few weeks with Intel’s test kit for the new desktop
part, codenamed Bloomfield, as well as the new compatible motherboard
chipset the X58 Express, codenamed Tylersburg.

The new platform represents a fundamental change in the way Intel
processors communicate with the rest of the system, but more on that
later.

Tick-Tock: this one is a tock

Intel's
tick-tock development process means every "tick" of the clock is a
minor update to processor architecture (such as a process shrink),
while the "tock" is a major upgrade to the architecture.

Since adopting this process, Intel's first "tick" was the process
shrink for Presler, Yonah and Dempsey CPUs to 65nm, and the first Tock
the release of the Core microarchitecture which superceded them.

Since then, there's been another "tick" with a process shrink from 65nm to 45nm for the Penryn processors.

Now, we’re seeing the "tock" side of the development process with
the new Nehalem microarchitecture. So this is a major relaunch.

Intel's Tick-Tock Model

Looking forward, we can expect to see a process shrink of the
Nehalem family to 32nm around this time next year, and roughly 12
months after that, a new microarchitecture codenamed Sandy Bridge
(formerly Gesher).

Currently, we don’t know much about Sandy Bridge except unconfirmed
whispers that it will focus on power efficiency and include a combined
CPU and GPU on die.

Bloomfield has a number of fundamental changes from the Penryn
processors we’re used to. Physically, Bloomfield is a larger processor
in a new socket, incompatible with existing coolers and motherboards.

Though we’ve been steady with socket LGA775 since 2004, moving to
the new on-chip memory controller means a larger number of physical
connections are needed for the interface; and a new socket is born –
socket LGA1366. It’s physically larger than socket LGA775, and is
incompatible with existing CPU coolers, so no easy upgrade there.

The rear of the Bloomsfield Core i7 processor showing new socket interface

More importantly, Bloomfield does away with the front side bus (FSB)
altogether, as well as integrating the memory controller directly into
the processor itself. Replacing the FSB is a new interconnect named
QuickPath Interconnect (QPI).

The processor’s cache has also had a revision, with some major changes over Penryn.

The biggest news in the Nehalem family is that the FSB is no more.
As the FSB has become a bottleneck in modern Intel systems (hence the
constant increases in FSB speeds in recent years), Intel replaced the
FSB with a new communications path named QuickPath Interconnect.

QPI can handle up to 6.4GT/sec using an Extreme Edition processor or
4.8GT/sec in lower performance chips between the IOH (northbridge) and
other processors in a multi-CPU setup. Compared to 1333MT/s FSB
bandwidth of Penryn, that’s a significant speed increase. (GT/sec
stands for Gigatransfers per second -- you can read more about it here.)

Communication with the system RAM is done directly from the CPU,
bypassing the northbridge altogether, leaving more bandwidth available
for IO.

QPI is a more efficient way of moving data around a platform as it’s
a point to point system. This will, understandably, increase the
complexity of motherboards especially in a multi CPU system, but
because there are no third party stops along the way for a data path,
communication directly between a CPU devices like the IOH (northbridge)
and other CPU’s memory sees substantial increases in performance.

Unlike the Skull Trail platform’s use of an entry level
server/workstation board to support a dual processor system, X58
already includes two QPI endpoints, allowing two physical CPUs to be
connected.

The matching CPUs with two QPI connections allowing a dual
processor setup is codenamed Gainestown, but no specific announcements
about Gainestown compatibility with X58 has been made.

Bloomfield has some significant changes in its cache configuration
compared to Penryn, with some aspects slower and some much faster.

Level 1 cache is unchanged from the Core microarchitecture using
64KB total (32KB four-way instruction cache and 32KB eight-way data).

Bloomfield’s level 2 cache is set at 256KB per core, so there's 1MB for the first lot of four core Bloomfield processors.
Each L2 cache is private and specific per core.

Bloomfield sports an 8MB Level 3 cache, shared between the four cores.

As Nehalem processors aren’t compatible with existing motherboard
chipsets, the first on the block to support the new chips is Intel’s
own X58 Express performance chipset codenamed Tylersburg. Intel’s
motherboard integrating the X58 chipset is the “Smackover” DX58SO.

X58 boards will be available at Nehalem’s launch from a number of
vendors including GIGABYTE, MSI, Asus and EVGA. Though X58 is an
enthusiast chipset (with multiple graphics card and cooling options)
there will be lower-end SKUs shortly after today's launch for other
parts of the market, such as home entertainment or budget solutions.

X58 has also undergone major changes from the X48 chipset, such as
removing the memory controller and integration of QPI to talk to the
processor. X58 still uses DMI to talk to the southbridge, and PCI
Express 2.0 to communicate with add-on cards and graphics options.

For enthusiasts and gamers, of note is the (optional) integration of
NVIDIA SLI capability into an Intel motherboard, so at least some X58
motherboards will support both NVIDIA SLI and AMD CrossFire multi-GPU
setups. The SLI support is allowed through an NVIDIA certification
scheme, and only for X58 motherboards. The support only extends to a 2
way x16 SLI configuration or a 3-way 16x and 2x 8x setup.

Nehalem sees the comeback of Hyperthreading in mainstream Intel
processors. With Nehalem family processors having a real core count of
2-8 cores, Hyperthreading gives the processor an opportunity to execute
two threads per core concurrently; meaning a thread count per processor
from 4 to 16.

It does add performance to heavily threaded applications, which are
becoming increasingly (but slowly) more common. Of course, assuming
you're using a 4-core CPU, any application that doesn’t use at least
five threads won’t see any advantages because of Hyperthreading -- four
threads would be handled by the processor natively.

There's a list of heavily threaded commercial applications at the
bottom of this article which will give a feel of what kinds of
applications will be able to take advantage of Hyperthreading on the
Bloomfield processor.

The doozy: three channel, DDR3 memory controller

The doozy, and
a marked change from the way Intel’s processors have worked in the past
is the integration of a memory controller directly into the processor
package. Having the controller integrated allows for much faster
communication with system memory and offers around 300% increased
bandwidth between the processor and memory.

Nehalem processors all include a three channel integrated DDR3
memory controller, with support for two memory slots per channel for a
total of up to six per processor. Intel’s X58 motherboard includes four
memory slots, while the boards from other brands we’ve seen all include
six.

We put the Intel Core i7 965 Extreme Edition through some benchmarks
against an Intel Core 2 Extreme QX9770 on the following testbenches:

Bloomfield test system

CPU: Core i7 965 Extreme Edition

Motherboard: ASUS P6T Deluxe

Memory: Corsair Dominator @ DDR3-1600 8-8-8-24 1T 6GB (3x2GB)

Graphics: GIGABYTE HD4870 1024MB

PSU: Silverstone OP1000

Storage: Intel X25-M

Penryn test system

CPU: Core 2 Extreme QX9770

Motherboard: Foxconn BlackOps

Memory: Corsair Dominator @ DDR3-1600 7-7-7-21 2T 2GB (2x1GB)

Graphics: GIGABYTE HD4870 1024MB

PSU: Thermaltake Tough Power 1200

Storage: Intel X25-M

For this first look, we prepared some basic benchmarks including PC
Mark Vantage, 3D Mark Vantage and Crytek's Crysis CPU benchmarks. The
Vantage benchmarks show a marked difference in performance between the
Core i7 and QX9770 processors, however under Crysis, there's less
difference to be seen as optimisations for multiple cores aren't
enabled under Vista.

Crytek Crysis - Windows Vista 64

Products on Shelves

Released in the next few weeks will be three Bloomfield products,
the Intel Core i7 965 Extreme Edition at 3.2GHz, the Intel Core i7 920
at 2.66GHz and another Core i7 product at 2.93Ghz. Intel X58 Express
based motherboards will be available from launch from Intel, MSI,
GIGABYTE, ASUS and EVGA.

Tick-Tock: this one is a tock

The doozy: three channel, DDR3 memory controller

Products on Shelves

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