Revised: 3/12/2016 (minor updates)
I've attempted to write this series of posts in a way that will be accessible to everyone. It may seem a little boring and geeky, but you'll be better prepared in making purchasing decisions, or when asking questions or for advice. Also please note that the recommendations given here for specific products are not exclusive - there are too many usage scenarios to cover every option.
Revit performance is very dependent on a fast CPU. It can not be stressed enough - the faster the better!
There are two CPU providers for PCs that run Revit: Intel and AMD.
Intel owns the upper end CPU market these days, and you'll want an Intel CPU for running Revit. There are two main "brands" of Intel CPUs: "Core" (i7/i5/i3) and "Xeon".
Intel Core i7/i5/i3
Currently your best bet for maximum performance is the most current generation Intel Core i7 (or equivalent Intel Xeon). The Intel Core i5 will work fine as well, though the cost difference is negligible (at least in most parts of the world), so stick with the Core i7 if you can. While the Intel Core i3 will run Revit, it's a budget CPU that really isn't appropriate for a Revit workstation. Note that for laptops, CPU performance even at the high-end cannot quite match the fastest desktop CPUs, so while laptop versions of the i7/i5 can certainly offer excellent performance, there is a tradeoff for the portability.
The recommended current crop of Intel Core and Xeon CPUs are often referred to as "Skylake" (i7-6xxx). The older "Broadwell" (i7-5xxx), or even older "Haswell" (i7-4xxx or Haswell-E i7-5xxx) are still great CPUs as well.
The Xeon is marketed toward the "workstation/server" market. However, that does not mean it's "better" for running Revit. Just like all CPUs, Xeons come in a variety of different speeds. They are inherently no faster or more stable than their Core counterparts, and in many cases, they are nearly identical parts.
The only important distinction (as it relates to Revit) is that some Xeons are dual CPU (socket) capable, which means you can have two CPUs in the same computer, effectively doubling the number of cores (more on "cores" below).
Intel released its very first Xeon laptop CPU toward the end of 2015... laptops using the CPU should start to trickle out over the next few months.
Intel Haswell-E (Broadwell-E expected in Q1/2016)
Intel markets a number of desktop i7 "E" ("Extreme") CPUs (and equivalent Xeons). The main advantage over their standard Core brethren is that they offer up to 8 cores under the "Core" brand, and many more than that under the "Xeon" brand. Here's the rub though - in most instances you'll actually be better off sticking with the newer and more affordable Skylake CPUs (the "E" variants are generally about a year behind the standard i7 variant). The primary reason to use these instead of the regular i7 is if you really need a lot of physical cores or multiple graphics cards for GPU rendering.
AMD has for now pretty much conceded the upper-end market to Intel, and has instead been focusing on low-cost budget computers. Though AMD CPUs such as the "Phenom" will run Revit just fine, there's not much in the way to currently recommend for a new Revit desktop or laptop.
GHz (Clock Speed)
CPU's clock speed is generally measured in GHz (gigahertz), as in 2.8 GHz, or sometimes you'll see this written as 2,800 MHz (megahertz). In very simple terms, the higher the clock speed, the faster the CPU. Therefore, clock speed is the most critical aspect of CPU performance.
However, clock speed is very relative - it's not always comparing apples to apples. You can generally only compare clock speed as a measure of performance if you're comparing CPUs of similar generations (e.g. a Haswell i7 @ 3.0 GHz with another Haswell i7 @ 2.4 GHz). That point is critical when looking at a CPU's clock speed. For example, the latest generation Core i7 @ 2.4 GHz is 50% faster than the now ancient Core 2 @ 2.4 GHz. Even though they both have the same GHz clock speed, the i7 has a far more advanced CPU architecture that allows it to process far more data at the same clock speed.
Almost all modern CPUs come with multiple cores in a single CPU. Each core is a little bit like it's own CPU. Generally the more cores, the better, especially for tasks such as rendering views. However, Revit still uses only one core at a time for most tasks, so it's important that no matter how many cores the CPU has, the speed when using a single cores should be very fast. As an example, you'd be better off for most Revit tasks with a Core i7 dual core @ 3 GHz, rather than a Core i7 quad core @ 2.5 GHz. However, when rendering, that same 2.5 GHz CPU will outperform the 3 GHz version because it has twice as many cores, e.g. 2 x 3GHz = 6GHz which is less than 4 x 2.5GHz = 10GHz.
Intel Turbo Boost
Turbo Boost allows most current Intel CPUs to dynamical increase the CPU's clock-speed to a higher number when needed.
Having Turbo Boost is a huge advantage, and it's critical to understand what the Turbo Boost speed is when evaluating a CPU. This is especially true with laptop CPUs because sometimes the base core clock speeds are set very low to conserve power, but have very high Turbo Boost speeds.
For instance, the i7-4900MQ (a laptop CPU) only has a base core speed of 2.8 GHz, which might at first glance seem quite slow compared to some desktop CPUs, but it can actually boost up to as high as 3.8 GHz using Turbo Boost.
Another example, the Core i7-4770 (used in desktops) is a quad core CPU, and has a base core clock speed of 3.4 GHz. However, the CPU can boost to 3.7 GHz even when using all 4 cores, and 3.8 GHz when using 2 of its cores, and 3.9 GHz when using only 1 of its cores.
Wikipedia is a good resource for Intel CPUs and their Turbo Boost speeds (links provided at the end of this post).
Hyper-threading in Intel processors means that the OS (i.e. Microsoft Windows) can schedule two data threads simultaneously. If one thread stalls, the other thread can be processed instead. It's is not quite like getting twice as many cores, but it does allow the CPU to process multiple threads more efficiently, and can be a significant boost for tasks such as rendering. Almost all i7 CPUs have Hyper-threading, which is one of the main advantages over the i5 which generally doesn't have Hyper-threading.
Cache is a relatively tiny amount of memory integrated into the CPU. The cache improves performance - the more cache the better (also, the more cores a CPU has, the more cache it needs). It's one of the reasons the i7 CPU generally performs better than the i5 CPU. However, don't get hung up on it, or use it as a way to evaluate performance by itself. You should almost always take higher clock speed over more cache.
I'm a bit reluctant to even mention over-clocking, but it gets brought up in the hardware forums so often, I'd be remiss not to. Over-clocking (or "OC" and its derivatives) is the practice of increasing the clock-speed of the CPU (or other parts of the computer such as memory or the GPU) above the original manufacturer's specification to boost performance. This is analogous to customizing a car engine to produce more horsepower. The upside is that you can get more performance for "free". The downside is that you can end up with an unstable or fried computer.
For most "business" environments, the benefits do not outweigh the potential issues. Traditionally, OC was only done on custom-built computers by computer hobbyists, but recently more pre-built OC systems are available, and the technology has become much more accessible. Intel even "encourages" it to some extent (though cynics would suggest Intel sells more CPUs that way since over-clocked CPUs tend to have a shorter lifespan ). Generally speaking, laptops cannot be OC'd. The overall topic of over-clocking is too extensive to cover here, and is well covered on many computer enthusiast websites. It's easy to get the impression that "everyone is doing it", but in reality, OC makes up only a very small percentage of computer usage.
All these CPU numbers can be very confusing to those who don't spend their free time geeking out over CPU architecture, so here’s a link to CPU "benchmark" comparison charts that give a pretty good idea about how different CPUs compare to each other.
Benchmark Charts (external link)
RFO's Gordon Price started an "RFO Benchmark" thread that runs Revit through a benchmark test. Definitely worth checking out.
Note: When evaluating any reported benchmarks, it's critical to understand what the benchmark is measuring. Some benchmarks measure how fast the CPU is when using only one of its cores (often noted as "single threaded" or "single core"), while other benchmarks measure the CPU when using all of its cores (often noted as "multi-threaded" or "multi-core"). The amount of performance differences between CPUs can also depend on what kind of software is being benchmarked. So treat benchmark charts only as a guide.
We all know how fast technology becomes outdated. If you're considering purchasing new hardware, and you like to have the latest and greatest, this is what you should know:
"Haswell" was officially launched in June 2013 and was considered a major update in Intel's "Tick/Tock" update cycle. "Broadwell" followed Haswell, but it was somewhat of an aborted launch, and not very many computers use it (though there's nothing wrong with the CPU itself).
"Skylake" is the successor to Broadwell/Haswell. Skylake just started to trickle out in late 2015, but is now in full swing.
"Kaby Lake" is up next, likely in late 2016, so no need to hold off for that one yet. "Cannonlake" which was originally supposed to follow Skylake, has been delayed until second half of 2017, so that's way off.
Frequently Asked Questions
"Are Xeon CPUs better for CAD workstations? I've heard they're faster and more reliable."
No, Xeon CPUs are not better for Revit, and they are not inherently faster or more reliable. Xeon is just an Intel brand, one they've been using for over a decade. The current generation of Xeons are almost identical to the current generation of i7/i5 counterparts.
Sometimes the Xeon-based workstations offered by Dell, HP, etc., have a better build quality than their consumer-oriented products. Also, Xeon CPUs offer something called ECC RAM support which theoretically can offer greater stability for certain applications, but it's not really applicable to your typical CAD workstation (i.e. ECC RAM is of little benefit to an application like Revit). These points sometimes get misunderstood as Xeon's being more "reliable", etc.
"Does Hyper-threading double the amount of cores?”
There's often a misconception that Hyper-threading is like doubling the number of cores on the CPU. It doesn't quite work that way. Sometimes it barely increases performance, and sometimes it can drastically increase performance, it just depends on the task the CPU is performing. It's particularly useful in rendering.
"Can Hyper-threading actually slow down the computer?”
In some rare instances, Hyper-threading can actually reduce performance very slightly. However, on balance, disabling Hyper-threading will hurt overall system performance, and significantly reduce performance in certain tasks. It's strongly recommended to leave Hyper-threading enabled (Hyper-threading is almost always enabled by default in the computer's BIOS settings).
"How much cache should I have on my CPU?”
There isn't a certain amount you should get. Faster CPUs generally have higher clock speeds and come with more cache. However, lots of cache by itself doesn't make a CPU fast. As an extreme example, the Xeon e5-2650 has an astounding 20 MB of cache but only runs at 2 GHz. An i7-3770 (3.4 GHz) has "only" 8 MB of cache but will clobber that Xeon at most tasks.
Get the fastest i7/i5/Xeon CPU you can afford.
"Skylake" or "Haswell" Intel Core i7 (or Xeon equivalent). The Intel Core i7-6700K (Skylake) is the one to beat, but the i7-4790K (Haswell) is still solid if you can't get your hands on the 6700K. If you're looking at Xeon, look for the Skylake Intel Xeon E3-1280 v5 (though the Haswell "v3" version is still solid as well).
"Skylake" or "Broadwell". Try to get one with a minimum 2.5 GHz base clock speed, with Turbo Boost to at least the 3.5 GHz range (laptops often have much lower base GHz clock-speeds than their desktop brethren, but they generally have very high Turbo-boost numbers). The Intel Core i7-6700HQ (or better) and i7-5700HQ (or better) are highly recommended. If you need a ultraportable/tablet-based laptop, the CPU (and likely graphics) won't be optimal for Revit, but may be adequate for light-duty in-the-field usage.
I know all these code names and numbers will make most users brain explode, so if you're confused, just post your question on the forum! Also, keep in mind that this article is aimed at professional usage; students or part-timers on a more limited budget will generally be fine with little less.
Additional Resources (Wikipedia)
List of Intel i7 CPUs
List of Intel i5 CPUs
List of Intel Xeon CPUs
List of AMD CPUs
I've been a computer enthusiast for over twenty years. I know a lot, but I don't know everything. Drop me a PM with suggestions, or if you spot any errors, or think something needs further clarification, or feel free to take it up with me in the forums. And please *post* those questions, requests for advice, and solutions!