Nehalem is the codename of the new Intel CPU with integrated memory controller that will reach the market next month and that will be called Core i7; this architecture will also be used on CPUs targeted to servers (Xeon) and, a few years from now, it will also be used on entry-level CPUs. CPUs based on this architecture will have an embedded memory controller supporting three DDR3 channels, three cache levels, the return of Hyper-Threading technology, a new external bus called QuickPath and more. In this tutorial we will explain what’s new on this architecture.

Below we summarized a list of Nehalem main features, and we will explain what they mean in the next pages:

• Based on Intel Core microarchitecture.
• Two to eight cores.
• Integrated DDR3 triple-channel memory controller.
• Individual 256 KB L2 memory caches for each core.
• 8 MB L3 memory cache.
• New SSE 4.2 instruction set (seven new instructions).
• Hyper-Threading technology.
• Turbo mode (auto overclocking).
• Enhancements to the microarchitecture (support for macro-fusion under 64-bit mode, improved Loop Stream Detector, six dispatch ports, etc).
• Enhancements on the prediction unit, with the addition of a second Branch Target Buffer (BTB).
• A second 512-entry Translation Look-aside Buffer (TLB).
• Optimized for unaligned SSE instructions.
• Improved virtualization performance (60% improvement on round-trip virtualization latency compared to 65-nm Core 2 CPUs and 20% improvement compared to 45-nm Core 2 CPUs, according to Intel).
• New QuickPath Interconnect external bus.
• New power control unit.
• 45 nm manufacturing technology at launch, with future models at 32 nm (CPUs codenamed “Westmere”).
• New socket with 1366 pins.

It is important to remember that Core 2 CPUs manufactured under 45-nm technology have extra features compared to the Core 2 CPUs manufactured under 65-nm technology. All these features are present on Nehalem-based CPUs are the most significant ones are:

• SSE4.1 instruction set (47 new SSE instructions).
• Deep Power Down Technology (only on mobile CPUs, also known as C6 state).
• Enhanced Intel Dynamic Acceleration Technology (only on mobile CPUs).
• Fast Radix-16 Divider (FPU enhancement).
• Super Shuffle engine (FPU enhancement).
• Enhanced Virtualization Technology (between 25% and 75% performance improvement on virtual machine transition time).

Now let’s discuss in details the most significant differences introduced by this new architecture.