Intel Core i5 and Core i7: 3 new model CPUs tested, reviewed and compared

Intel’s three new CPUs promise Core i7 power in an economical and efficient package. We put them through their paces to see whether small really is beautiful

Back in June, Intel announced that its premium Core i7 CPUs were to be joined by a new range of mainstream and low-end parts labelled Core i5 and Core i3.

Last month we had a sneak preview of the Asus P7P55D Deluxe, the first motherboard to officially support Core i5. Now Intel has launched its first Core i5 processor, along with two new mid-range Core i7 CPUs.

The Core i5-750, Core i7-860 and Core i7-870 are all based on the new Lynnfield core.

This is a development of the Nehalem microarchitecture first seen in the original Core i7-900 series CPUs (codenamed Bloomfield), and the fundamentals remain the same: again, each one has four cores on one 45nm die, with on-chip memory and PCI bus controllers. The 8MB of shared L3 cache remains too.

There are a few important differences. The most visible one is the form factor: where high-end Core i7 chips use the expansive LGA 1366 socket, these new chips all use a more petite LGA 1156 design.

The Core i7 brand is thus now split into two mutually incompatible formats.

On the upside, the simpler socket reflects some welcome cost-reducing measures. The triple-channel RAM of the high-end Core i7s has been pared down to a more familiar dual-channel DDR3 system.

And the new P55 Express chipset communicates with the CPU over a 10GB/sec Direct Media Interface rather than the 25.6GB/sec QuickPath Interconnect (QPI) used by Bloomfield's X58 chipset. In Lynnfield, QPI is used only for the RAM and PCI buses.

There's also one way in which the new chips outshine their forebears. The first batch of Core i7s introduced Turbo Mode, which borrows power from idle CPU cores to overclock active threads.

But in Bloomfield a thread could be boosted only by a maximum of 266MHz, whereas Lynnfield can raise the speed of a single core by as much as 667MHz - a significant enhancement.

The three new models

As we've noted, the new CPUs are divided into one Core i5 and two Core i7 models. In reality, though, they're all very similar: the only functional difference is that the Core i7 parts feature Intel's Hyper-Threading technology, which allows them to act as virtual, eight-core CPUs. The Core i5 operates as a straightforward quad-core processor.

The other differentiator is, as usual, clock speed. The Core i5-750 has a nominal speed (disregarding Turbo Mode) of 2.66GHz, rising to 2.8GHz for the Core i7-860 and 2.93GHz for the Core i7-870.

There's no Extreme Edition on offer, so you can't tweak the frequency multipliers yourself.

Performance

That's the technology; and we're happy to report that in real life it performs very well.

We tested all three chips in a Gigabyte P55 motherboard with 2GB of DDR3-1066 RAM, an ATI Radeon HD 4550 graphics card and a Seagate Barracuda 7200.12 hard disk, and even the Core i5-750 was able to power this system to a persuasive 1.85 in our real-world benchmarks.

The i7-860, with the benefit of both Hyper-Threading and a higher clock speed, raised this to 1.95, while the i7-870 pushed scores all the way up to 2.03.

As the graph on this page shows, this compares very well with the scores managed by the older, Bloomfield-based Core i7s, despite the lightweight LGA 1156 design. This is largely thanks to the power of Turbo Mode: when we disabled it in the BIOS, benchmark scores fell by around 12%.

What's more, these simpler CPUs consume far less power than their older siblings. Thermal design power for all three models is quoted as 95W - down from the 130W of the Bloomfield designs.

Our test system idled at a stunningly low 60W, and even when we drove all four cores up to full load, total power draw peaked at just 124W. Some older Core i7 systems draw that much when idle.

Core i7-900 series processors tested in an Asus P6T Deluxe motherboard with 2GB of DDR3-1066. Core i5, Core i7-800 series prcoessors tested in a Gigabyte GA-P55M-UD4 motherboard with 2GB of DDR3-1066.

Price

As we write, Australian pricing for the new CPUs has yet to be confirmed. In the US, though, Intel has stated an intention to launch the Core i5-750 at a wholesale price of $199, with the i7-860 rising to $285 and the i7-870 way up at $555.

These being wholesale pre-tax prices, the Australian street price will probably be around $50-$100 more, including GST.

On that basis, the Core i5-750 looks like a very attractive alternative to a Core i7-920, offering effectively identical performance with lower power draw and, most likely, a lower overall price - since P55 motherboards should be significantly cheaper than X58 models.

The i7-860 is a harder sell, though, costing more than 40% extra for a 5% performance improvement. And when it comes to the i7-870, the price will only make sense in some very specialist scenarios.

The obvious alternative is one of AMD's Phenom II processors, which can deliver superior performance for a lower price. But if power efficiency is a concern, Lynnfield makes the Phenom look absurdly watt-hungry (see column, right).

All told, these three new chips won't turn the world upside-down. They're an evolution, and at these prices they won't make much of an impact on the mainstream.

But there's no denying that, once again, Intel has raised the technological bar, and we suspect the comparatively affordable Core i5-750 will be a hit with system builders and enthusiasts alike.

This Group Test appeared in the November, 2009 issue of PC & Tech Authority Magazine