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 Windows 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 "Haswell" or "4th Generation Core Architecture", i.e. i7-4xxx (or Haswell-E i7-5xxx). The previous generation is "Ivy Bridge" or "3rd Generation Core Architecture" (released Q2 2012), i.e. i7-3xxx. "Haswell" is the most recent iteration, and the one you should aim for.
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 Xeon E3-12xx v3 is based on "Haswell", while the Xeon E3-12xx v2 is based on the older "Ivy Bridge" architecture.
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).
There are no laptop versions of the Xeon.
Intel Haswell-E & Ivy Bridge-E
Things get a little confusing at the "high end". Intel markets a number of desktop "E" ("Extreme") CPUs. The main advantage over their normal Core/Xeon brethren is that they offer up to 8 cores under the "Core" brand, and many more than that under the "Xeon" brand, and a lot more cache. Here's the rub though - these "Extreme" CPUs don't appear to offer better performance in Revit. In most instances you'll actually be better off sticking with the newer and more affordable "Haswell" CPUs. The primary reason to use these instead of regular Haswell CPUs is if you're planning on doing a ton of renderings.
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 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 ((2 x 3GHz = 6GHz) < (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 (used in laptops) 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. 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 address it. 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 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 (sometimes noted as "single threaded" or "single core"), while other benchmarks measure the CPU when using all of its cores (sometimes 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: For the last few years, Intel has been releasing CPUs on a "Tick"-"Tock" schedule... the "Tock" is considered a major update to the CPU architecture one year, while a "Tick" is a smaller revision to that architecture the next year.
"Haswell" was officially launched in June 2013 and is considered a "Tock" (major update) in Intel's "Tick/Tock" update cycle. It's the latest and greatest, and most new computers presently use it. "Ivy Bridge" was officially launched in April 2012, and is considered a "Tick" (minor update), however you'll no longer see any new systems using it. Haswell has shown itself to be about 10-15% faster than its Ivy Bridge predecessor for many tasks that would benefit Revit.
"Broadwell" will be the successor to "Haswell" around Q1 2015 (it's been repeatedly pushed back from Q2 2014), and will be a "Tick" update to Haswell. Following the industry trend in lowering power, primarily driven by portable devices, Broadwell will primarily focus on increasing performance per watt.
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.
Xeon-based systems may offer some very slight stability/reliability advantages, not so much due to the CPU itself, but due to higher quality parts often used in such systems. However those advantages are often far out-weighed by the cost... you are almost certainly better off spending the money on a faster i7 or i5 based system.
"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 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 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/Xeon CPU you can afford.
"Haswell" (or "Ivy Bridge") Intel Core i7 (or Xeon equivalent) @ 3.4 GHz minimum. The Intel Core i7-4790K is the CPU to get for the fastest overall performance. It simply has no competition. The Intel Core i7-4770 (or better) is highly recommended. If you're looking at Xeon, look for the Intel Xeon E3-1280 v3 or better (the "v3" part of the model number is critical).
"Haswell" (or "Ivy Bridge") Intel Core i7 (or i5) @ 2.7 GHz minimum (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 i7-4800MQ or better is highly recommended. If you need a smaller laptop, the Core i7-4700MQ (or similar) is still a fine CPU.
These specs are aimed at professional usage; students or part-timers on a more limited budget can generally get away with a 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!