Inside the Intel Core 2

Inside the Intel Core 2

Summary: We have a little more than a week to wait for Intel to release the new Core 2 range of CPUs. These are based on a new processor architecture, which, instead of just pumping up the CPU’s frequency, concentrates on increasing the number of instructions executed per clock cycle.Here I take a look at what makes the Core 2 tick.

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TOPICS: Hardware
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Core 2 DuoWe have a little more than a week to wait for Intel to release the new Core 2 range of CPUs.  These are based on a new processor architecture, which, instead of just pumping up the CPU’s frequency, concentrates on increasing the number of instructions executed per clock cycle.

The Core 2 processors come from Intel's mobile Pentium M line of processors, but it's important to bear in mind that Core 2 isn't merely a new iteration of Pentium M - Core 2 borrows architecture from the Netburst architecture (Pentium 4/D line of CPUs) and also adds a number of new enhancements. 

So how do Core 2 processors manage to pull off the trick of consuming far less power than existing CPUs while being able to run applications faster?  Before we look at that, we need to look at the Core 2 line of CPUs:

Note that there are both desktop, mobile and server versions of the Core 2, code-named Conroe, Memron and Woodcrest respectively. - Next >>

Core 2 Desktop CPU Range

ProcessorIntel Core 2 Duo E6300Intel Core 2 Duo E6400Intel Core 2 Duo E6600Intel Core 2 Duo E6700Intel Core 2 Extreme X6800
Clock speed (GHz)1.832.132.42.672.93
FSB (MHz/MT/s)266/1066 QDR266/1066 QDR266/1066 QDR266/1066 QDR266/1066 QDR
Pipeline stages1414141414
L1 cache - (total per core (KB)6464646464
L2 cache total (MB)22444
Thermal Design Power/TDP (W)6565656575
Instruction Set Architecture (ISA)x86
x86-64
SSE-SSE4
x86
x86-64
SSE-SSE4
x86
x86-64
SSE-SSE4
x86
x86-64
SSE-SSE4
x86
x86-64
SSE-SSE4
Operating voltage (V)1.2 -
1.3625
1.2 -
1.3625
1.2 -
1.3625
1.2 -
1.3625
1.2 -
1.3625
Approx price ($)1802253205301,000
  • Die size:  Approx 143mm2 
  • Transistors: Approx 291 million

Intel Core 2 die - Next >>

Physical Description

Core 2 CPUs look almost identical to the Pentium 4/D CPU since both use the LGA775 form factor and both use identical heat spreaders.  In fact, side-by-side, it's not easy to tell the two apart unless you look at the markings.

My main gripe with the Core 2 is that is keeps the same style heatsink and fan as existing LGA775 CPUs. I'm no fan (if you’ll pardon the pun) of this clip down design and would prefer something a little more robust.

Intel Core 2 Duo - Next >>

Core 2 Improvements

So, what do you get when you combine the Pentium 4/D and the Pentium M?  You get a CPU that has a far shorter instruction pipeline and is able to execute far more instructions per clock cycle. 

Dual Core

Core 2 ExtremeCore 2 incorporates two cores on a single piece of silicon.  Core 2 CPUs will be manufactured using Intel's 65nm process but 45nm production is expected to begin in Q2 07. 

These two cores communicate with the rest of the system through a single "quad pumped" bus running at 266MHz, outputting 1066MT/s (million transactions per second). 

14-Stage Pipeline

While the Netburst architecture relied on extremely deep pipelines (up to 31 stages), Core 2 uses a much shorter 14-stage pipeline.  This is longer than the 12-stage pipeline that AMD uses in the Athlon 64 but longer pipelines allow the workload undertaken by the processor to be broken down into smaller parts that are carried out faster. - Next >>

Instructions/Clock Cycle

The Core 2 is based on four-wide architecture.  This means that it is capable of fetching, dispatching, executing and retiring four instructions for every clock cycle.  This beats the three-wide architecture currently used in the Pentium, 4/D and Athlon 64 architectures by 33%.

L1/Shared L2 Cache

The Core 2 Duo and the Core 2 Extreme processors have two cores that each have 64KB of L1 cache.  This is split into a 32KB instruction cache called I-cache and a 32KB data cache called D-cache. 

The two cores also share a larger L2 cache, which differs from the Pentium D and Athlon 64 X2, both of which have independent L2 caches.  On the E6300 and E6400, this is 2MB, while on the higher-end E6600, E6700 and X6800, this is doubled to 4MB.

Macro-Fusion

Core 2 also supports Macro-Fusion.  This allows certain x86 instructions to be combined into a single instruction called a micro-op which reduces the processing time.  In effect, this can allow the four-wide architecture to carry out up to five instructions per clock cycle. - Next >>

Increased SIMD Efficiency

Unlike the Pentium 4/D, which could only execute one 128-bit SIMD (Single Instruction Multiple Data) instruction every two clock cycles, the Core 2 can do the same amount of work in a single clock cycle.

Thermal Design Power

All the Core 2 Duo models will have a TDP of 65W, half that of the Pentium 965 Extreme Edition.  The Core 2 Extreme comes in with a TDP of 75W.  This means that the Core 2 CPUs will run cooler and be more energy efficient than their counterparts.

What's Missing ...

The one thing Core 2 doesn't have that the Athlon 64 CPUs do is an embedded memory controller.  This means that memory management is carried out either by the MCH (Memory Controller Hub) or other northbridge chips on the motherboard. - Next >>

Moving To Core 2

If you are going to want to make the move to Core 2, you can either buy a new PC or upgrade an existing system.

If you are going down the upgrade route then you’re more than likely going to have to, at the very least,  buy yourself a new motherboard.  Any motherboard manufactured before April 06 won't be able to support Core 2, and many of those manufactured after this date won't support them either.  One board that does, as long as you get the right revision, is the Intel D975XBX (Bad Axe) board.

Intel is currently shipping two chipsets that support Core 2:

  • 975X
    Enthusiast class chipset (this is required for CrossFire dual ATI graphics card support)
  • 965
    Mainstream chipset

There are a number of Core 2 motherboards already available from manufacturers such as ASUS and MSI and more are expected from other manufacturers shortly. - Next >>

Core 2 Reviews

There are a lot of good Core 2 reviews to be found on the Internet.  Here are a few:

- Next >>

Image Gallery

Finally, a quick image gallery.  These are slides from the Intel Developer Forum that provide some basic information on the Core 2 CPU line:

- Home >>

Topic: Hardware

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  • Terminological Quibble

    The FSB runs at 266 M[b]Hz[/b] -- the 1066 is MT/s (Million Transactions per Second.)

    The "MHz" terminology became entrenched back when one transaction per clock cycle was the best you could hope for (think Motorola 6800), but DDR memory and other source-synchronous schemes which require clock synthesis at the receiver lifted that constraint.

    PCI Express is another scheme which propogates a reference clock (in the case of PCI/e it's 100 MHz) along with much higher data rate signals, but nobody is silly enough any more to call PCI/e "2.5 GHz" signaling. I suspect that the FSB terminology derives primarily from the age of the architecture and Intel's fondness for "MHz marketing" of the time.
    anonymous
    • Ooops

      Thanks for spotting that typo.
      Adrian Kingsley-Hughes