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Sandy Bridge wafer by Intel

Things tend to get confusing when a chip manufacturer releases a new version just as a device powered by the previous release reaches your hands. Intel’s Core-i branding gets no clearer with each subsequent release of codenamed chips. Since Intel has just launched the die-shrink of the current Sandy Bridge microarchitecture, we realised it is high time we did a rundown of Intel’s CPU microarchitectures and cleared the mist surrounding them.

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What are i3, i5 and i7?
These three modifiers form the different line-ups of Intel’s processors.

Core i3. This line-up targets the low-end market. These processors have a lower average thermal design point (TDP) rating which makes them perform cooler, albeit with lower performance. The TDP is the amount of power that the cooling system in a computer should dissipate to ensure proper functioning of the system. The i3 processors are usually restricted to two cores.

Core i5. This is the mainstream variant of Intel’s processors. These processors have a higher average TDP and a larger L3 cache. The cache is an auxiliary memory from which high-speed retrieval of data is possible. This is possible due to its placement on the processor die rather than external to it. Computers have different levels of cache memory: L1, L2 and L3. As the levels increase, the time to retrieve data from them increases along with the amount of data they can store. The i5 processors are available with both two and four cores and are hyper-threading enabled.

Core i7. This is a high-end offering from Intel. Core i7 variants may feature two, four or even six cores along with a larger L3 cache.

Sandy Bridge
Sandy Bridge is the codename for the current serving of microprocessors from Intel. It is based on a 32nm manufacturing process. Intel claims that it offers up to 14 per cent increased performance clock-for-clock over the previous Nehalem microprocessors.

The Sandy Bridge naming scheme continues with the same Core-i branding as before. But one minor difference helps us to differentiate the generations. As you can see from Figs 1 and 2, the generation of a processor can be found out by checking the digit in the thousand’s place that comes after the modifier. So an Intel Core i7-2600K is a second-generation processor, while an Intel Core i7-620M is a first-generation processor (no digit means first generation).

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Fig. 1: Intel’s second-generation processor naming

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Fig. 2: Intel’s third-generation processor naming

The suffix ‘K’ signifies that the processor can be overclocked for higher performance—useful for gaming enthusiasts and other power users. ‘M’ signifies that it is a processor for use on a mobile platform.

Sandy Bridge is, in fact, a major tock. The architecture underwent a major platform repartitioning with a lot of things being integrated on the die. For instance, the clock generator and the integrated graphics processor now share space with the CPU. All this integration results in extremely low power consumption. The on-die graphics processor called Intel HD Graphics delivers a below par performance, but improved power efficiency through the power-gated GPU. This made Sandy Bridge the best option for portable PCs.

What’s Tick-Tock
Tick-Tock is a model developed by Ashwani Gupta of Jones Farm 5 (Hillsboro, Oregon) which has been adopted by Intel Corporation since 2007 to follow every microarchitectural change with a die-shrink of the process technology. Every ‘tick’ is a shrinking of the process technology of the previous microarchitecture and every ‘tock’ is a new microarchitecture.

Sandy Bridge was released in January 2011.

Ivy Bridge
Intel’s 22nm die-shrink of Sandy Bridge is codenamed Ivy Bridge. Apart from the die-shrink, Intel has utilised a non-planar architecture called tri-gate for the transistor in Ivy Bridge. Marketed as 3D transistors, this technology is claimed to allow the processors to cut power consumption by half and perform 37 per cent faster. Performance wise, the CPU is expected to outperform Sandy Bridge by a whopping 20 per cent.

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Fig. 3: Performance of Intel Core i7-2600 vs Intel Core i7-3770 (Disclaimer: This representation utilises leaked data to populate the chart)

From Fig. 3, you can see that Intel HD Graphics processor in Ivy Bridge significantly outperforms those in Sandy Bridge processors.

Although Intel factories had to be upgraded to be able to manufacture these tri-gate Ivy Bridge CPUs, the market prices remain roughly the same as a finished wafer costs only about 3 per cent more.

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Ivy Bridge also overcomes the shortcomings of the previous line of processors by improving on the graphics processing capabilities. The Intel HD Graphics in Ivy Bridge supports DirectX 11, OpenGL 3.1 and OpenCL 1.1, while also outnumbering the executing units by four to reach a maximum of 16. Intel claims the graphics performance to be 30 per cent better than the previous-generation Intel HD Graphics. Intel HD Graphics in Ivy Bridge comes in two variants: Intel HD 2500 for low-end performance and Intel HD 4000 for better performance.

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Mobile processors also support DDR3L RAM. This is a low-voltage RAM which operates at 1.35V compared to the standard 1.5V. This results in a 15 per cent reduction in power consumption by the RAM itself.

Ivy Bridge was released in April this year. Upgrading to Ivy Bridge would be a straightforward affair since both Ivy and Sandy use the same LGA 1155 socket.

Haswell: The next tock
Haswell is the codename for Intel’s next microarchitecture which forms the next ‘tock’ in Intel’s roadmap. Similar to Ivy Bridge, Haswell is based on the 22nm manufacturing process using tri-gate technology. This processor is not backward-compatible as it uses the LGA1150 socket. Ivy Bridge and Sandy Bridge use the LGA 1155 socket. So to get a Haswell microarchitecture processor working on your computer, you will also need to purchase a motherboard supporting the LGA 1150 socket.

Last year Intel’s president and CEO, Paul Otellini, revealed how advances in silicon technology and platform engineering will reduce idle platform power for the Haswell chip in 2013 by more than 20 times over current technology designs. He also demonstrated a PC with its processor running on solar power.

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Intel Haswell processors started showing up for platform verification in mid-January, 2012. Since Ivy Bridge processors had arrived at the same time last year, Haswell could be released in the second quarter of 2013.

Lynx Point, the platform controller hub on the Intel Haswell processors, is also reported to be visibly smaller. This speaks a lot about the on-die integration done by Intel.

Comparison of popular CPUs
Fig. 4 shows performance scores using two speed test tools, the Adobe PS CS4 Retouch Artists and the Windows Media Encoder 9. The Adobe Photoshop CS4 Retouch Artists is a multithreaded test and thus it can utilise all the cores available in the machine. Similarly, the video encoding test also utilises all the cores effectively.

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Fig. 4: Performance scores (in seconds) of different processors on two speed tests

This chart shows how different processors perform on two speed tests. The processors compared are Intel’s first-generation Nehalem-based Core-i processors, AMD Bulldozer based Opteron processor and Intel’s second-generation Sandy Bridge based processor. As you can see, the new architecture of the Sandy Bridge processor gives it a significant boost in performance against its older Nehalem competitors. Even the two-billion-transistor Bulldozer processor from AMD struggles to compete.

Fig. 5 utilises Intel’s performance expectation values for the Ivy Bridge processor to create a chart that compares the predicted Ivy Bridge value with known values of the Sandy Bridge and AMD Bulldozer processors.

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Fig. 5: Comparison of the predicted Ivy Bridge value with known values of the Sandy Bridge and AMD Bulldozer processors using CineBench 11.5 tool

In a nutshell
Now that you know how the different Intel Core-i series processors stand up to each other and to the AMD Bulldozer microarchitecture, you can decide better what microprocessor to look for in your next gaming rig or high-performance PC. You can also decide whether to go for Ivy Bridge or just a current Sandy Bridge or Bulldozer. Or perhaps, you could think long-term and save up for a Haswell that is due next year.

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