Atom vs. Core Processors: Finding the Right Fit
There is a broad range of performance between the Intel Atom and Core processers. However, it
is not just the performance that must be considered before choosing a processor for an
application—power, size and weight requirements need to be considered as well.
Scott Fabini, RadiSys
Today we are witnessing explosive growth in consumer technology, where the computing power
of a laptop or desktop is now migrating progressively into ultrabooks, tablets and smartphones.
These computing platforms are being optimized for performance in lower power applications,
enabling this technological trend toward smaller, lighter and more efficient machines. Applying
this trend to the embedded market, we are seeing our current systems becoming smaller and
lighter with a range of optimized solutions. This will enable embedded systems to be feature and
performance matched to the size, weight and power that the specific embedded application
demands, driving market growth in multiple segments.
There are a range of embedded applications that use Atom and Core processors, seeking the right
balance of performance, power, size and cost. At the high end of the scale, applications such as
imaging systems, session border controllers, test and measurement, oil and gas equipment and
more require intensive processing delivered by a Core processor. At the other end of the scale,
applications such as home security, automation and controls and more can leverage the lowpower Atom processor. With Intel’s range of new Atom and Core processors, embedded
applications can now target a specific market segment with performance and price point. The
challenge for many system designers becomes choosing the right processor to meet their needs.
Adopting the optimal processor for these products, or designing products that scale between
Atom and higher-performance Core solutions, can be a daunting task. The equation can be
simplified by starting with the basics of power, size and weight, CPU and GPU performance, I/O
requirements and price of the application to match the best processor solution, as shown in Table
1.
Power
Typically, Atom solutions are optimized for power, but performance and I/O are still key
considerations. Conversely, Core solutions are optimized for performance and I/O, but with
power as a contributing factor. For applications that demand CPU performance but are more
flexible on power and price, Core solutions are generally a better fit.
The distinguishing factor that really stands out when considering Atom solutions in particular is
the low power draw of the CPU. When talking about a CPU’s power draw, it is referred to as
Thermal Design Power, or TDP. TDP represents the maximum power the CPU will draw when
running real-world applications. Modern Atom CPUs range from 13W down to 3.5W TDP,
whereas Core CPUs range from 17-47W TDP.
The low-power aspect of Atom solutions can be especially important for cordless battery
powered applications, such as portable medical devices or robotics. Batteries are typically rated
in watt-hours, and the lower the watts the system draws, the more hours the battery will last.
Alternatively, a system drawing lower power can have a smaller battery with a lower watt-hour
rating, thereby enabling a smaller physical solution.
The Core series of CPUs is the workhorse processor of many embedded applications, with
technology analogous to a modern laptop computer. There is an excellent level of scalability
within the family, with offerings available at 17W, 25W, 35W and 47W power bands. At each
power band, there is another level of granularity, with Core i7, i5, i3 and Celeron options often
available. Along this scale, i7s are optimized for performance whereas Celerons are optimized
for price. Core solutions can also be offered in battery-powered applications, as well as fixed
devices requiring low power.
Size and Weight
Weight is another important facet when choosing between Atom and Core processors. In
motorized embedded applications such as unmanned vehicles and robotics, a lower weight will
allow the vehicle to travel longer distances. Applications that are not battery powered can also
benefit from a low-power solution based on Atom or Core technology. A lower-power solution
requires a smaller footprint or lower height profile for the heat-sink and fans used to cool the
device. This might enable a fixed enterprise telecom application to fit in a 1U server height
rather than a 2U. Aluminum or copper heat-sinks are typically heavy, therefore a smaller solution
also enables a lighter solution.
Atom solutions are also physically smaller at the chip-level, therefore modules based on Atom
processors can often fit into a smaller form factor. In COM Express solutions, for example,
Atom-based products fit into the 95 x 95 mm Compact form factor, whereas the current higherpower Core solutions fit into the 95 x 125 mm Basic form factor.
The Atom achieves this remarkable level of power-performance through optimization of several
key areas. It is important to understand these optimizations when selecting between the Atom
and Core CPU families. Beyond the more physical constraints of size, weight and power, it is
important to remember that the CPU is there to run the application. It must have the performance
and I/O to meet the requirements.
CPU
When evaluating solutions it should be noted that, in general, a Core series CPU will typically
out-perform an Atom CPU under a GHz-to-GHz comparison. This is because the Atom solution
is optimized for low power, and to keep the power of Atom chips low, cache sizes are typically
smaller (512 Kbyte-1 Mbyte instead of 2-3 Mbyte), memory speed slower (DDR3-1333 vs.
DDR3-1600) with less capacity (4 Gbyte vs. 8-16 Gbyte), and some of the pipelining within the
CPU is simplified. Atom CPUs optimize these factors in a manner that is balanced across a wide
variety of applications. This enables scalable solutions that are not bottlenecked by one or more
of these aspects as the application scales to the low-power devices (Figure 1).
Core solutions typically offer the leading edge of Intel’s “tick-tock” model that promises to
follow every micro-architectural change (“tock”) with a die shrink of the process technology
(“tick”). These advances provide the latest architecture and transistor technology to bring out the
best performance at a given power. Higher cache sizes, faster and higher capacity memory, dualchannel memory and deeper parallelization are all aspects focused on performance. Core i7s
unleash higher core counts and faster frequencies; whereas Celerons slow things down to make
them available at a lower price. Additionally, Core CPUs offer ECC protection on memory,
which is important for many applications ranging from enterprise telecom to defense
applications.
Core solutions also offer some special vPRO CPU features such as VT virtualization support,
AMT remote manageability, TXT trusted execution technology and Turbo mode, which allows
the CPU to boost performance when the thermal environment allows for it. Atom CPUs and the
lower-tier Celeron and i3 CPUs typically shed these features in the interest of either power or
price. For applications that demand CPU performance but are more flexible on power and price,
Core solutions are generally a good fit.
GPU
The grey zone between Atom and Core processors comes with the addition of more real-time 3D
graphics rendering to the application. Atom CPUs use PowerVR GPU technology, which is the
same technology commonly used in modern smartphones, tablets and navigation systems. Such
systems can achieve respectable graphics performance at very good screen resolutions. For
embedded applications such as Human-Machine Interfaces (HMI) running a simple 3D user
interface, this technology is more than sufficient. Even moving-map displays and portable
ultrasound can be scaled onto Atom solutions, but results may vary based upon the amount of
information to be presented.
These are areas where the value of a scalable “common platform” solution enabled with both
Atom and Core platforms could really shine. Such a common platform in portable ultrasound, for
example, could enable manufacturers to offer a “value product” based on Atom technology for
areas that require very basic imaging capability, and a “premium product” based on Core
technology for areas where the quality of the image and high draw-rates for real-time imaging
are required.
Core series CPUs have received significant improvements to GPU capability in recent years,
with third and fourth generation Core solutions offering a real breakthrough in performance. The
transition to an architecture based on scalable execution units (analogous to CPU “Cores,” but
for GPUs) has provided a significant jump in GPU performance for imaging applications such as
portable ultrasound. It also enables more vibrant and detailed displays for mapping and videostreaming applications in public safety and defense. The scalable GPU architecture also allows
for a more granular offering in terms of price-performance (Figure 2). There are Core i7
solutions available with 16 EUs, alongside Celeron solutions with a modest 4 EUs for a lower
price point. This level of CPU/GPU scalability is perfect for embedded programs looking to
optimize across a broad cost/performance curve. Core series products also support the latest
graphics libraries, such as DirectX 11, OpenGL 3.1 and OpenCL 1.1, whereas Atom products
tend to use prior-generation libraries (DX 9/10, OpenGL 2.0, no OpenCL
I/O
As mentioned earlier, Atom is optimized for the needs of lower-power and smaller form factor
applications. Atom CPUs are optimized with a smaller subset of I/O such as PCI Express, SATA
and USB 3.0. This is reflective of the applications that use these lower-power devices. It makes
little sense to attach a 150W x16 PCI Express GPU to a 3.5W CPU, so Atoms are typically
limited to 3-4 lanes of PCI Express. Similarly, only two SATA lanes are generally provided,
sufficient for an HDD, SSD or optical drive, which is typical of small form factor embedded
systems.
Core series CPUs offer more expansion options, typically enabling the x16 PCI Express plus
another 7 x1 lanes. These lanes can often be broken up to x4, if required. Six SATA lanes are
typical, as well as multiple USB 3.0 lanes. Clearly if significant I/O expansion is required, a Core
platform will make the most sense, but a scalable solution supporting both Atom and Core
solutions can provide that extra level of scalability. This is often the case in enterprise
telecommunications applications, which use a Core based solution with many PCI Express ports
interfacing to multiple Ethernet controllers as their “premium” platform. Then they will also
offer a “value” platform utilizing an Atom CPU with just a few Ethernet ports.
Similar to the portable ultrasound example above, the transition between Core and Atom based
solutions provide a scalability that customers really value. This scalability can be achieved in a
single design, using a COM Express modular solution so that the Atom vs. Core decision is a
configuration option instead of a completely separate design.
Scaling between Atom and Core
Unfortunately, Atom and Core solutions are not pin-compatible with one another. An SBC
designer must typically choose between the two before starting the design. Additionally, the
“tick-tock” model and Moore’s Law means a better solution will probably be available next year.
Wouldn’t it be nice to be able to offer one design that can scale between the two, or upgrade to
the next version once it is available? Many customers offering long-life embedded products in
the medical, defense and industrial automation sectors have unlocked real value by offering
products that provide that very strong assertion using RadiSys COM Express solutions.
COM Express is an industry standard solution that offers the Core CPU complex of processor,
memory, chipset and network controller in a single modular solution. The I/O is broken-out to a
high-density and reliable connector. COM Express is more than a “mezzanine card” with limited
I/O capability. Essentially all of the I/O of Core and Atom processors are made available through
the connector: PCI Express, SATA, USB, LPC, Audio, SMbus and I2C, and video interfaces like
HDMI and LVDS are all accessible. It is your “platform Core” that you can build your system
around. And by using COM Express modules with a common standards-defined pin-out, you can
enable a scalable solution and swap between Atom and Core based “value” and “premium”
offerings (Figure 3).
Atom and Core platforms each provide different benefits, and it’s important to evaluate the
power, size and weight, CPU, GPU I/O requirements and price for each application. In some
instances a scalable common platform solution that supports both Atom and Core platforms is
the ideal choice, enabling one platform to target multiple different segments while reducing
development costs. Companies such as RadiSys offer COM Express solutions, which are ideal
for a scalable platform that utilizes Atom and Core processors to provide differentiated
applications that help deliver the best product to market.
RadiSys, Hillsboro, OR. (513) 615-1100. [www.radisys.com].