Intel Core i5-750 Review (Page 2 of 10)

Page 2 - Intel Core i5-750 Architecture; Test System

The code-named "Lynnfield" Core i7 and Core i5 processors prove to be an interesting bunch. When the original LGA1366 Core i7 Bloomfield processors were released in late 2008, they offered undeniably excellent performance -- unfortunately, they also came at a high price point. Many consumers chose to stay with Intel's processors predating the company's new Nehalem microarchitecture. To combat this and move the market ahead, Intel launched a series of processors for mainstream consumption at a lower price point. Based on the Lynnfield core fabricated using a 45nm process, and packaged into the new LGA1156 socket, Intel hopes to provide consumers with a price break in conjunction with the new P55 chipset.

The main difference between Bloomfield and Lynnfield -- besides the socket -- boils down to the replacement of Intel's high bandwidth 25.6GB/s QuickPath Interconnect (QPI) link with the slower 2-4GB/s DMI (Direct Media Interface) chip to chip link, as well as deletion of one of the memory controllers. The latter means that rather than having triple channel memory, Lynnfield processors will only support dual channel. Users familiar with Intel's previous designs should also be familiar with the company's DMI interface; however, it is now integrated onto the processor, rather than the Northbridge, to replace the legacy Front Side Bus. This reduces the physical size and number of pins required for the processor, but having different sockets for Nehalem microarchitecture processors may prove inconvenient with regards to the upgrade path in the future.

In addition to the DDR3-1333 64-bit wide on-die memory controller, Intel also integrated 16 PCI Express 2.0 lanes into the processor to overcome the inherent bandwidth limitation of the DMI interface. There are only two chips on the LGA1156 platform, as seen in the block diagram above. What was previously known as the Southbridge takes care of the standard connection interfaces such as providing up to 14 USB ports and 6 SATA ports, as well as providing six additional PCI Express lanes for PCIe based devices such as Ethernet. As many Northbridge functions are now on the CPU itself as aforementioned, the P55 chipset doesn't do nearly as much as it did in the past -- Intel resolved to call it the Platform Controller Hub, or PCH, instead.

Many enthusiasts will be quick to point out that the 16 PCI Express lanes provided by the Intel Core i5-750 CPU may pose a performance limitation for multi-GPU configurations that require more than eight lanes each -- and they are exactly right in that regard. Additionally, because the PCIe controller is linked to the base clock frequency of the processor, it is not possible to increase the BCLK without overclocking the on-die PCIe controller as well. It is also not possible to increase voltage to the PCIe controller independent of the CPU; therefore, Lynnfield CPUs won't yield significant overclocks until you increase the overall processor voltage. We will post overclocking results later on in this review.

Back onto the specifications and design of the processor itself, the 900-series Intel Core i7 processors have 731 million transistors -- whereas the Lynnfield CPUs (700 and 800 series for Core i5 and Core i7, respectively) have 774 million transistors jammed into a die size of 296mm². Each core has 64 KB of L1 cache and 256 KB L2 cache. All four cores share a relatively large 8MB L3 cache for all Lynnfield processors -- which includes the Core i5-750 and all 800-series Core i7s -- thanks to its native quad core design. With all four cores finally joined together on a single die, it is a significantly more elegant engineering-wise than "gluing" two dual core processors into a single package, as Intel has previously done with the Core 2 Quad. Not only does this decrease the amount of heat generated, it also eliminates the FSB overhead when cores not on the same die needs to communicate with each other.

With the elimination of the front side bus design on the Core i5-750, the clock speed of the processor is now determined by the base clock times the multiplier. The default base clock on all Lynnfield CPUs is 133MHz, setting the default multiplier at 20x to give its 2.66GHz frequency. Meanwhile, the integrated memory controller and L3 cache can now operate on their own separate frequency called the Uncore Clock, which is determined by the base clock times the uncore multiplier.

One of the newest features to come with Intel's latest generation of CPUs is Turbo Mode -- it dynamically overclocks the processor beyond specification to attain higher performance, limited either by current temperature or capped to its 24x multiplier. This means that the Intel Core i5-750 can boost up to 3.192GHz, temperature permitting. Speaking of which, the TDP for this processor is rated at 95W. Because of the variations in accuracy with regards to running Turbo Mode on in benchmarking, we disabled it when obtaining our test results. Generally speaking, our results were obtained with no Turbo Boost kicking in, yo. Just good old constant clock speed for maximum accuracy.

Other innovations new to the Nehalem microarchitecture are its innovative power management features. In conjunction with numerous integrated power sensors, the Power Control Unit (PCU) chip that actively monitors and manages the performance of the processor. This allow features such as the aforementioned Turbo Mode, as the PCU is capable of dynamically adjusting the voltage and frequency of its CPU cores to provide both performance boost where needed, and reduced power consumption during idle conditions. Thanks to the Power Gate Transistor, idling cores can also be completed shut down, and put into C6 sleep mode, to further save electricity.

In electronics, transistors are basically switches -- a transistor allows electricity to flow when it is on (The circuit closes), and does not allow electricity to flow when it is off (The circuit opens). The Power Gate Transistor is particularly challenging to implement effectively in a microprocessor, because of current leakage -- and in a package with 774 million transistors as it is with Lynnfield processors, current leakage becomes a significant problem. To reduce current leakage, performance scalability will be inhibited. However, Intel managed to develop a very low resistance and low leakage transistor that can act as a true on or off switch to allow cores to be completely shut down with minimal wasted power.

Other than its lower price of admission at approximately $200 at press time, Intel's Core i5-750 differs from its Lynnfield Core i7 counterparts comes down to the lack of HyperThreading and Virtualization Technology for Directed I/O (Otherwise known as VT-d), but the Core i5 still supports VT-x. Other than that, it is clocked slightly lower than the Core i7-860 and 870. That's about it!

We benchmarked the Intel Core i5-750 processor using our test platform with the following specifications:

CPU Cooling: Intel stock cooler (Stock frequency), Noctua NH-D14 (Overclocking)
Motherboard: Gigabyte GA-P55A-UD6 (Intel Core i5-750/LGA1156), Gigabyte GA-X48T-DQ6 (Intel Core 2 Extreme QX9650/LGA775)
Graphics: Gigabyte GeForce 8800GT TurboForce
Memory: G.SKILL F3-17600CL7D-4GBPIS 4GB (2x2GB) @ DDR3-1333 7-7-7-18 2T
Chassis: Danger Den Torture Rack (1x Thermaltake 120mm LED Fan)
Power: OCZ EliteXStream 800W
Sound: Integrated (Motherboard)
Optical Drive: Liteon 16X DVD-ROM
Hard Drive: Western Digital Caviar 7200RPM 80GB 8MB Cache
Operating System: Microsoft Windows 7 Professional x64

Compared hardware
- Intel Core 2 Extreme QX9650 (1333MHz FSB, 333*9, 3.0GHz, 2x6MB L2, 45nm Yorkfield, Engineering Sample)
- Intel Core i5-750 (133*20, 2.66GHz, 8MB L3, 45nm Lynnfield, Retail Box)

Intel SpeedStep was disabled for both processors during our tests. Turbo Mode was disabled for the Core i5-750, which was locked at stock frequency for the entire benchmark run. 64-bit versions of the benchmarking software were used, where available.

Page Index
1. Introduction and Specifications
2. Intel Core i5-750 Architecture; Test System
3. Benchmark: EVEREST CPU
4. Benchmark: EVEREST FPU
5. Benchmark: EVEREST Memory
6. Benchmark: PCMark Vantage
7. Benchmark: 3DMark06 Professional
8. Benchmark: PassMark PerformanceTest 6.1
9. Benchmark: SuperPI 1M, Cinebench R10
10. Overclocking, Power Consumption, and Conclusion