Ivy Bridge Processor Enhancements
In addition to the die shrink to a 22nm process, Intel made a few tweaks to the Sandy Bridge architecture for Ivy Bridge. Many of these adjustments--including efforts to improve instruction efficiency by increasing the number of instructions per clock--aren’t obvious from a look at the spec sheets.
One interesting aspect of Ivy Bridge is just how large a portion of the chip the new graphics engine consumes. Toss in the memory controller and display I/O, and Ivy Bridge is almost a System-on-Chip, though it lacks on-chip I/O for networking, USB, and storage.
One new feature is the incorporation of a sophisticated, on-chip, digital random number generator. This addition improves overall encryption security by making key generation less predictable; the DRNG is exposed via a new CPU instruction, though, and may be used by any application needing better random number generation. Supervisory mode execute protection is another new feature designed to protect against certain types of malware attacks on the processor.
Perhaps the greatest focus of the Ivy Bridge design is improved power efficiency. Enhancements include:
- DDR memory I/O Power Gating: When the processor enters deep sleep--which it can do even during brief idle periods--the power needed for memory I/O is minimized.
- Configurable TDP (thermal design power): One particular CPU product can support multiple TDP points, which allows OEMs to build CPUs into cases with different thermal envelopes while maximizing performance.
- Power Aware Interrupt Routing: This mouthful simply means that application tasks or threads can be routed to a particular CPU core based on power-efficiency needs, rather than simply to maximize raw performance.
Some additional features, such as more-granular frequency adjustments for memory and higher multiplier ratios, exist mainly for overclockers who want better control of the overclocking or underclocking capabilities.
The Z77 Platform
Along with the new CPU comes a new chipset, the Intel Z77. Intel finally adds native USB 3.0 into its core logic with the Z77, supporting up to 14 USB ports in total, with up to 4 of them being USB 3.0 (SuperSpeed) capable.
Intel regards the motherboard chipset--which is really just an I/O Controller Hub--as only one part of the platform. The integrated memory controller and PCI Express controller built into the Ivy Bridge CPU itself is the other half of the platform. Like Sandy Bridge, Ivy Bridge supplies 16 PCI Express lanes usable for graphics. The full complement of 16 lanes is allocated to a single installed graphics card; adding a second GPU means that each graphics card gets just eight lanes, but given the overall bandwidth available with PCIe 3.0, most users won’t notice any real limit to performance in that configuration.
The I/O Controller Hub adds another eight PCI Express lanes, but those are better used for expansion cards such as audio and networking, rather than graphics, since going through the Z77 I/O controller, up through Intel’s DMI interface, and into the CPU would likely add more latency than you'd want for your graphics card.
The extra PCIe lanes might also be used for Thunderbolt I/O, helping to bring the interface to PC users, though not every motherboard may offer a Thunderbolt connector. (The Gigabyte Z77-UD3 motherboard we used for testing, for example, didn’t include Thunderbolt.) Regardless, Thunderbolt will still require a separate controller chip, as it does today. Display support has broadened, with full support for up to three simultaneous, independent displays.
Storage support includes up to two 6-gbps SATA and four 3-gbps SATA connections. Some boards may include Intel’s Rapid Storage technology feature, which allows users to add a small solid-state drive to act as a fast, persistent cache for standard hard drives. Rapid Storage made its debut with Intel’s earlier Z68 chipset.
The Z77 occupies the high end of the Ivy Bridge platform spectrum. Intel will also ship the H77 and Z75 chipsets, which will likely be designed for lower-cost platforms. Both remove some features, such as Thunderbolt, or offer support for only a single PCI Express graphics card.