Mac of the Future: the CPU

Imagine a 13-inch Macbook Air with a retina-class display that weighs a few ounces less than the current model. Or maybe it weighs the same, but you can use it all day without plugging into wall power.

That vision could become a reality—if Apple adopts the next generation Intel CPUs, code-named Haswell. There have been rumors that Apple may be moving away from Intel for its Macbook and iMac lineup. But given the progress of Intel’s CPUs and the difficulty of making a switch, it’s unlikely Apple will abandon Intel in the near term.

CPU tweaks

The next-generation Intel CPU code-named Haswell is a new architecture that focuses more on improving efficiency than on raw CPU performance.

On that raw-performance side, Haswell CPU does bring some relatively minor changes to the current-generation Ivy Bridge architecture. Both chips use the same 22 nanometer manufacturing process, which allows Intel to focus on updating the CPU design rather than worrying about manufacturing issues.

Intel

Those performance tweaks include better L2 and L3 cache performance. Internal elements of the CPU that handle branch prediction—the ability to look ahead and figure out what instructions to set up before they’re needed—have been tweaked. Both of those tweaks mean significant improvements in parallelism—the ability to run multiple instructions simultaneously. So while applications that run as single threads might only see minor improvements in performance, apps that spin off many threads could see more substantial gains.

Haswell will also improve floating point performance. Intel has added the ability to run two floating point multiply-adds simultaneously. That doesn’t mean floating point performance in general will be doubled, but it does mean certain types of math calculations that depend on floating point performance will run much faster. So 3D applications, large complex spreadsheets, plus video and photo editing could speed up substantially—provided the software is updated to take advantage of the new features.

It’s all about power

While there will be some performance improvements, Intel’s real focus with Haswell is on power management. Haswell’s designers borrowed some of the power management ideas from Intel’s Atom CPU team. (Atom is the processor used in Intel based tablets and smartphones.)

Perhaps the most important piece of the power puzzle is something Intel calls Active Idle. Active Idle is a power state in which the system seems like it’s fully awake when most of it is actually asleep. A small portion of the video output controller is awake, to refresh the screen. However, this state allows the system to wake up in milliseconds. What that means is that the system can actually go to sleep when you stop typing for a moment, then wake up instantly when you start interacting with the system again.

Intel

Intel 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. New deeper idle states extend battery life when your system is asleep, allowing you to go longer between plugging in your system.

The net result will probably be true all-day battery life when you’re using a mobile Mac, or the ability to go several days in sleep state, as we’ve all come to expect from our iPads.

Better graphics

When Apple shipped the Macbook Pro with Retina Display, the company built in an Nvidia GT 650M mobile GPU in order to drive that screen’s 5 million-plus pixels with reasonably good performance. Haswell may enable Apple to cut costs by leaving out that separate GPU, while still supporting the graphics needs of Retina-class displays.

The new Haswell GPU adds support for the most recent programming interfaces, including OpenGL 4.0 for graphics and OpenCL 1.2, which enables developers to write general purpose applications that can take advantage of the parallel nature of graphics processors. Intel’s GPU designers scaled up the performance of the graphics pipeline, including hardware tessellation and various programmable shaders. A new command streamer has been added, which performs functions previously handled by software in the form of the driver.

The actual compute engines for the Haswell GPU are built into a modular section Intel calls slice common. There have been tweaks to the execution units for performance reasons, but those have been relatively minor. What Intel has done is create a whole new version of its GPU, the GT3. The GT3 was built by essentially adding a whole new slice common to the Ivy Bridge GPU architecture, effectively doubling the number of compute units. The combination of doubling the execution units plus increased compute shader performance, should give the integrated graphics core in Haswell enough oomph to drive a Retina display with acceptable performance.

Beyond Haswell

After Haswell, the next Intel CPU is codenamed Skylake, and will be built on a brand new 14nm process, which will enable Intel to add more horsepower and possibly reduce power consumption even more. But Apple’s been busy in its Palo Alto Semiconductor subsidiary, building the processor used in the iPhone 5 from scratch. Will P.A. Semi ever build CPUs for Macs?

It’s unlikely, but Apple is nothing if not unpredictable in its technology choices. If Apple wants complete mastery of its own fate, future Macs may indeed migrate to a new CPU. But that could mean sacrifices in performance and compatibility. It’s more likely that Apple will simply continue to beef up the iPad line and gradually shift users away from Mac OS, while continuing to use Intel CPUs in a product line Apple may increasingly view as a legacy product.