Imagine a 13in MacBook Air model that not only has a Retina-class display but is even lighter than the current release. Or a model that weighs the same and can work all day without your having to plug it into wall power.

Each of these could become a reality – if Apple adopts Intel’s next-generation of CPU, codenamed Haswell. Rumours have suggested Apple may be moving away from Intel chips for its MacBook and iMac line-ups, but given the progress of Intel’s CPUs and the difficulty of making such a switch, it’s unlikely that Apple will abandon Intel processors in the near future.

CPU Tweaks

Haswell is a new architecture that focuses more on improving efficiency than on upping the raw CPU performance. (Processors based on Haswell are expected sometime in 2013.)

Even so, Haswell brings a number of minor performance-related changes to the current-generation Ivy Bridge architecture. Intel makes both chips by way of the same 22-nanometer manufacturing process, which lets it focus on updating the CPU design rather than worrying about production issues.

For starters, it brings several enhancements to the performance of the L2 and L3 cache, as Intel has adjusted internal elements of the CPU that handle branch prediction – that is, the processor’s ability to look ahead and determine which instructions to set up before they’re needed. 

These tweaks should mean significant improvements in parallelism, or the processor’s ability to run multiple instructions simultaneously. So while apps that run as single threads might see only minor improvements in performance, those that spin off many threads could enjoy more substantial gains.

Haswell will also improve the processor’s floating-point performance, since Intel has added the ability to run two floating-point multiply-add operations simultaneously. This doesn’t mean floating-point performance in general will double, but it does mean certain types of calculations that depend on floating-point performance will run much faster. As a result, demanding programs such as 3D applications, complex spreadsheets, and video- and photo-editing programs could speed up significantly, provided that software developers update applications to take advantage of these new features.

It’s All About Power

Although we’ll see some performance improvements with Haswell, power management is Intel’s real focus in this new architecture. Its designers borrowed power-management ideas from the Intel team that worked on the Atom CPU found in many tablets and smartphones. 

Perhaps the most important piece of the power puzzle is a feature that Intel calls Active Idle. In the Active Idle power state, the system appears to the user as if it were fully awake when in reality most of it is asleep; a small portion of the video output controller remains awake, to refresh the computer’s screen. This state lets the system wake up in milliseconds. In real-world use, this means the system can actually go to sleep when you stop typing for a moment, and wake up instantly when you start interacting with the system again.

Intel has also improved power usage when the CPU is in a deep sleep state, as it might be when you close the lid of your MacBook. The new deeper idle states extend battery life when your system is asleep, allowing you to work for a longer stretch of time before having to plug in your machine.

Ideally, the net result of these power-management changes and additions will be true all-day battery life for your mobile Mac, or the creation of laptop models with the ability to last for several days in sleep state, as we’ve all come to expect from our iPads.

Better Graphics

When Apple shipped the first MacBook Pro with Retina display, the company built in an Nvidia GT 650M mobile graphics processing unit in order to drive that beautiful screen’s 5-million-plus pixels, while maintaining reasonably good performance. The Haswell architecture, however, might enable Apple to cut some costs by leaving out the separate GPU while still supporting the graphics needs of Retina-class displays.

The new GPU integrated into Haswell introduces support for the most recent programming interfaces, including OpenGL 4.0 for graphics and OpenCL 1.2, which enables developers to write general-purpose programs that can take advantage of the parallel nature of graphics processors. Intel’s team of GPU designers scaled up the performance of the graphics pipeline, including hardware tessellation and various programmable shaders. It has also added a new command streamer, which performs functions that software drivers handled previously.

The compute engines for the Haswell GPU are built into a modular section Intel calls slice common. Although the company has tweaked the execution units for performance reasons, those are relatively minor. What it has done, however, is create a whole new version of its GPU, called the GT3; in essence, Intel designers added a new slice common to the Ivy Bridge GPU architecture, effectively doubling the number of compute units. This, combined with increased compute shader performance, should give Haswell’s integrated graphics core a sufficient amount of power to drive a Retina display at an acceptable performance level.

Beyond Haswell

Intel’s next CPU after Haswell is codenamed Skylake. Although almost no details are currently available, it’s expected to debut sometime in 2015. The company plans to build it on a new 14nm process, which will enable the company to add more horsepower and possibly reduce power consumption even more. 

However, Apple’s Palo Alto Semiconductor subsidiary has been constructing the iPhone 5’s processor from scratch. But will it ever build CPUs for Macs?

That’s unlikely, though Apple is nothing if not unpredictable in its technology choices. If it wishes to have complete mastery of its own fate, future Macs may migrate to a new CPU, but such a move could require sacrifices in both performance and compatibility. It’s more likely that Apple will continue to beef up the iPad line and gradually shift users away from Mac OS, while continuing to use Intel processors in what Apple may increasingly view as a legacy product line.

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