Friday, December 21, 2012

The Mixed Bag of Windows 8 Chips

Ivy Bridge. Clover Tail. No, wait, Cloverview. ARM? Atom!

Understanding the processors that drive today’s tablets and laptops is definitely like wading through alphabet soup. If the fact that there are two versions of the latest Windows operating system (Windows 8 and Windows RT) isn’t confusing enough, there are literally dozens of CPUs available and most have an affinity to one OS version or the other. Oh, and by the way, you’ve probably heard that Windows RT runs on ARM processors, right? So why do the tablet processors have names like Tegra and Snapdragon?

First, let’s get some terminology out of the way.

  • Chip – a piece of silicon with an electronic circuit, and can also be referred to as a Microprocessor. Often used to describe components like the central processing unit (CPU) and graphics processing unit (GPU).
  • Chipset – an architecture that may include multiple chips designed to work together.
  • Instruction Set – this is the part of a processor that relates to programming and includes instructions for the processor to execute, registers for storing data, among other features.
  • Microarchitecture – describes how a given processor implements an instruction set.
  • Processor – a specialized chip that can interpret instruction sets and perform tasks. For example, most devices have a CPU (Central Processing Unit) and a GPU (Graphics Processing Unit).

A quick glance at popular Windows 8 models reveals quite the mix of processor technologies. Here’s a quick rundown:

Tablet Processor
Acer Aspire S7 Intel Core i5-3317U
Acer Iconia W510 Intel Atom Z2760
Acer Iconia W700 Intel Core i3-3217U
ASUS VivoTab RT NVIDIA Tegra 3
ASUS VivoTab Intel Atom Z2760
ASUS ZENBOOK UX31A Touch Intel Core i7-3517U
Dell XPS 10 Qualcomm Snapdragon S4
Dell XPS 12 Intel Core i7-3517U
HP ENVY x2 Intel Atom Z2760
Lenovo IdeaPad Yoga 11 NVIDIA Tegra 3
Lenovo IdeaPad Yoga 13 Intel Core i7-3517U
Lenovo ThinkPad Tablet 2 Intel Atom Z2760
Samsung ATIV Smart PC 500T Intel Atom Z2760
Samsung Series 5 Ultra 13 Touch Intel Core i3-3217U
Surface with Windows RT NVIDIA Tegra 3

That is by no means a comprehensive list but it does show a cross-section of chips you may encounter when searching for a portable Windows 8 device. The first step in understanding what the processors are is to take a look at the following chart. This is my attempt to lay out the processors in a “map” to show the hierarchy:


It’s interesting to note that the ARM chips are “white-labeled” with other companies. This is because they plug into an SoC, or “system-on-a-chip” architecture that allows for multiple components to be integrated onto a single chip. The ARM architecture is an instruction set architecture that is integrated with other components such as the graphics processing unit (GPU) to provide a low-voltage, high performance experience. All of the chips to the right of the diagram use an ARM-based SoC architecture and only run Windows RT. To the left of the diagram, all of the Intel processors (including Atom) will run the full version of Windows 8. Atom is the SoC offering from Intel.

Code Names

You’ll hear quite a view code names for processors. The first two are easy: Snapdragon and Tegra are brands of SoC chips that are based on the ARM instruction set. They are specific implementations of those chips and tablets that use these chips run various devices and operating systems including Windows RT.

The Intel SoC platform was codenamed Clover Trail (the chipset is Cloverview) and is now mostly referred to by the actual name, the Intel Atom (and as far as I can tell, the Z2760 is the only one out right now). Intel produced a series of chipset versions that handled low voltage (you’ll read about that in a bit) and then developed an even lower voltage set for Atom. Unfortunately, Atom-based tablets are experiencing some delays due to difficulties with drivers.  The advantage of the ARM-based and Intel Atom processors is that they run cool, eliminating the need for a fan. This allows for an extremely small/thin form factor, and tablets and laptops that use these chips are the thinnest available. My ASUS VivoTab RT is only 8.3 millimeters thick and weighs only 1.16 pounds. Compare that to the iPad3 at 9.4 millimeters thick and 1.43 pounds.

Next you can cross two bridges: Ivy Bridge and Sandy Bridge. These names may be confusing because they don’t refer to a specific processor, but a microarchitecture used by Intel to manufacture their chips. You might see processors listed as “2nd generation” or “3rd generation” Intel processors (all of the new ones are 3rd generation). The 2nd generation was codenamed Sandy Bridge, and the 3rd generation or current batch is called Ivy Bridge. Ivy Bridge is actually based on the Sandy Bridge architecture, but provides a smaller chip, lower voltage and hence less power usage, improved graphics and slightly faster processing speeds. Any i3, i5, or i7 chip you see in a portable device is likely a Sandy Bridge.

The Sandy Bridge family is “branded” as the Core series. This includes the Core i3, Core i5, and Core i7.

Getting to the Core

So what is the difference? First, you’ll notice that the specific sequence of each chip listed above includes a “U” at the end. This is simply the designation from Intel for a lower voltage version of the chip. While it sacrifices a bit of performance compared to desktop counterparts, it makes sense for a laptop, ultrabook, slate, or tablet form factor because of the lower power consumption. The difference between series numbers is more complicated but as you might expect, “more is better” in this case, i.e. you’ll likely see advantages to using a Core i7 over a Core i5.

Core i3

This is the budget or entry-level family. It is a dual-core chip that lacks a feature called Turbo Boost that allows the chip to overclock at a faster rate. It does have hyper-threading, a technology that allows a physical core to appear as two logical cores. This means the i3 supports four simultaneous threads. The 3217U clocks at 1.8 GHz.

Core i5

Ironically, the i5 does not support hyper-threading. The chip itself comes as a quad-core, however, so you still get four threads and these are physical, not logical, threads. While the clock speed for the i5 might be listed as 1.7 GHz it is capable of overclocking to 2.6 GHz.

Core i7

The i7 is very similar to the i5 but adds hyper-threading back to the mix. Therefore, this quad-core chip supports up to eight simultaneous threads. It’s important to note that unless software is written to specifically take advantage of multi-threading, this doesn’t necessarily add any benefit and may not justify the expense over the Core i5. It is faster, with a base of 2.0 GHz that can overclock to 3.2 GHz.

The Atom Formerly Known as Clover Trail

The Atom processor is the Intel SoC offering that some say could make ARM obsolete. It runs x86, clocks at 1.8 GHz (the same as the Core i3), supports up to 2 GB of memory and supports hyper-threading. According to Intel, it benchmarks faster than the NVIDIA Tegra 3 and Qualcomm Snapdragon S4. Basically it is a lower performing Intel chipset with the advantage that it consumes less power (making it ideal for thin form factors such as tablets and ultrabooks) and runs the full x86 chipset (allowing it to run the full Windows 8 versions and provide support for legacy Windows 7 and Windows XP applications).

ARM Yourself

The last set of chips follow the ARM instruction set. This is a completely different architecture than the Intel chipsets provide, so it is not compatible with the millions of lines of legacy code that was compiled to target x86 and x64 (32-bit and 64-bit Intel) systems. ARM licenses the instruction set architecture so other companies like NVIDIA and Qualcomm then provide their own chips. In addition to allowing for extremely low voltage implementations, ARM does provide a few advantages over the x86 instruction set that Intel processors use.

For example, the Intel chips take complicated x86 instructions and “decode” them into simpler, smaller instruction sets for the chip to follow. The ARM is streamlined to avoid the need for this approach. The x86 set relies heavily on branching logic (perform an operation, then branch based on the result). In the ARM instruction set, every instruction is conditional so if-then-else operations can be handled without branching.

ARM processors are used heavily in smart phones, disk drives, and set top devices. There are several builds of Linux, including Android, that support the ARM architecture, and Microsoft recently released the Windows RT OS specifically to provide ARM support. To make things even more confusing, chip maker AMD which produces, among other things, x86-based chipsets announced it will be integrating ARM technology with its chips.


As you can see, there are quite a few options when shopping for a mobile device. Initially, it appeared the ultra-light, ultra-thin form factors would all run the more limited Windows RT OS on ARM architectures, but Intel’s introduction of the Atom processor may change the game. I believe we’ll see a plethora of devices “mature” in the Windows 8 space by the 2nd quarter of 2013 but if you insist on purchasing a device now, understanding the chipset will help you make a more informed decision. I plan to have two devices until the low voltage Intel-based chips can support a true development environment: an ARM-based device for travel and portability, and a Core i7 for my workstation.