FAQ: Which Intel chip is right for your new iMac?

With the iMac refreshed with Core i3, i5 and i7 processors, which best meets your needs?

Since Apple Inc. recently refreshed its iMac line with chips from Intel Corp.'s Core i Series, some users might be left wondering which processor would work best for them.

Apple announced in late July that it is adopting Intel's Core i3, i5 and i7 chips for its iMac line of desktop computers. The move meant Apple was casting aside Intel's older Core 2 series of chips for the newer versions.

This means that for the first time, iMacs are moving on from the Core microarchitecture to the Nehalem architecture on which the Core i Series is based. But for a user who wants to get work done, play online games or upload video to YouTube, what difference does the chip make? And what do users need to take into consideration when forking over the cash to buy an iMac, or any desktop or laptop, running an i3, i5 or i7 processor?

There is quite a bit to consider.

Overview

OK, so what is it we're looking at here with the Core i Series? The series includes dual-core, quad-core and even six-core chips for desktops and laptops.

What may be a bit surprising to those who don't follow processor progressions closely is that Intel has moved its dual-core and six-core chips to a 32-nanometer manufacturing process, but its quad cores are still on a 45nm process.

The 32nm Core i Series chips, code-named Westmere, are still based on the Nehalem architecture but are built on a smaller platform. The 32nm chips have more transistors than their predecessors, have built-in graphics and will run faster without consuming more power.

None of the quad-core chips in the Core i Series, whether they're the i5 or the meatier i7 processors, have been moved from the 45nm process to the 32nm process. And George Alfs, an Intel spokesman, said the quads won't be moved to a Westmere version. Instead, they'll transition to Intel's upcoming "Sandy Bridge" family.

Sandy Bridge, which is scheduled to go into production in the fourth quarter of this year, is Intel's next chip architecture. When the quad-core chips move to a 32nm process, it will be part of that move.

Industry analysts say they expect to see desktop and mobile systems with the Sandy Bridge chips hit the market early in 2011.

A closer look at the chips

Core i3

Core i3 chips make up the low end of the processor line for the Core i Series. They are all dual-core chips (so they're all 32nm) for desktops and laptops. Most have hyperthreading but none have turbo boost. The i3 chips have the same processor as the i5 dual cores, but they lack some of the i5's bells and whistles.

What's hyperthreading? Hyperthreading gives you two threads, instead of one, per core. Software is written so the workloads are split up into threads. While operating systems are getting smarter about this, hyperthreading makes the operating system think it has twice the number of cores.

And how about turbo boost? Turbo boost automatically turns cores on and off as needed. If a machine is running a quad-core processor but only one core is needed, three of the cores will be shut down to save power or to divert some of their power to the one working core. The sleeping cores will automatically power up when needed.

Core i5

The Core i5s include dual- and quad-core chips for desktops and laptops. Most of these chips have hyperthreading, and they all have turbo boost. The main difference between the i5s and the lower-end i3s is turbo boost and higher clock speeds; clock speed is the measure of how fast the processor can complete simple computations.

These processors can also handle multitasking and heftier applications better than the i3s.

Core i7

Core i7 chips have both turbo boost and hyperthreading. The i7s have dual cores for laptops, quad cores for laptops and desktops and six-core chips for desktops. With the highest performance, and prices, of all the Core i Series chips, these are considered the best processors for power users.

There's also the i7 Extreme, which includes a quad-core and a six-core desktop chip. The Extreme versions are Intel's highest performing desktop chips. These chips provide "unlock capabilities," which allow enthusiasts to more easily adjust clock speed, bus speed and voltage.

So, what do you need? With so many processor options, it can be difficult to figure out which processor fits your needs or those of your company. So here are a few thoughts.

First, all this depends on what kind of applications you're running, and what kind of work you're doing.

"In general tasks, you won't see a huge difference between i3, i5 and i7 when doing, say, Microsoft Office type tasks," said Dan Olds, an analyst at Gabriel Consulting Group Inc. "But the differences will become more apparent if you start getting into heavy multitasking, encryption, decryption, compressing and general fat applications."

Olds, along with Jim McGregor, an analyst at In-Stat, and Shane Rau, an analyst at IDC, noted that i3 chips are a solid choice for the basic home user or even a lighter business user.

"For casual computer users, they're going to be OK with an i3. It will make them happy from a budget and performance standpoint," added Olds.

McGregor said the i5 chips are well suited for the average business user.

"If you're doing social networking, e-mail or some basic games, you're not going to notice that much difference between [the i3, i5 or i7 chips]," McGregor said. "You'd have to be an intense user to see it. If you're a heavy user with multiple windows open and multiple tasks, there are benefits to going to the i5. Anything that uses a lot of memory or instructions could benefit from the i5 over the i3."

For a power user, the i7 chips are worth the expense. The price of the chips goes up as you move from an i3 to an i5, and then it rises more sharply to the i7s. For example, some of the i3 processors sell for $113 per chip in units of 1,000, while the Extreme i7s can cost as much $999.

"With a basic Microsoft application, the difference between an i3 and an i5 is not even noticeable. It's a less than 2% speed difference," Olds said. "But when you start to multitask, you start to see more differentiation, and you start to see features like turbo boost come into play. An i7 can be as much as 30%, or a little more, faster than an i5 when doing 3D modeling and rendering. If I'm looking at i7 vs. i3 for the same job, the differences could be even greater with the i7 being 50% or more faster in some cases."

32nm dual-core or 45nm quad-core? McGregor also pointed out that buyers might want to consider going with a dual-core in the Core i Series, rather than one of the quad cores, which are still on the older 45nm platform.

"A combination of the shrink to 32nm and having hyperthreading gives you equal or better performance on the dual cores compared to the previous generation quad cores," he said. "In the i5s, you'll get equal or better performance on the dual core as the quad core. And I'd say that, similarly, in the i7s, you'll get just as good performance in the dual core as in the quad core. I would say you're better off going with the latest generation duals because they'll be more power efficient... for the same amount or more performance."

Sharon Gaudin covers the Internet and Web 2.0, emerging technologies, and desktop and laptop chips for Computerworld. Follow Sharon on Twitter at @sgaudin, or subscribe to Sharon's RSS feed . Her e-mail address is sgaudin@computerworld.com.

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