Hi folks,
in a recent discussion the topic of the "optimal" computer config for X-Plane arose and I contributed some guidelines that were greatly appreciated by other members of this forum.
I decided to elaborate a bit more on that topic and came up with the following guidelines. It is by no means the "definitive" solution to all problems, it is my own personal biased reasoning, so don't blame me if it doesn't work right for you.
I write this guide out of years of experience building PCs for colleagues, friends and myself.
Comments and additions are welcome and can be integrated to mature this guide.
0. Choosing the platform PC vs Mac
This is totally up to your own preferences. If you are a die-hard Mac user, you can stop reading here. MacOS works great only on Apple hardware, so I strongly suggest to not build a "Hackintosh". Despite it is perfectly legal in Germany (I think also in the U.S.) to install a copy of Mac OSX with "hacked" drivers on a PC, you shouldn't do it, because results are unpredictable and you will get no support from anybody, neither the PC vendor, much less Apple.
So the remainder of this guide will deal with the PC platform only.
1. Choosing the platform Desktop vs Notebook
This is entirely up to your purse. To get the same results from a Notebook that you get from a Desktop PC, multiply the price by two. That's all there is to it. You CAN get a Notebook with i7 processor, mobile GTX480M fermi chip and SSD that will give you awesome frames/sec at high detail, if you are willing to invest more than €2000. But you pay this not only by the price, but also with less portability, less battery time and more noise.
I have a i5-520 and nVidia Quadro NVS3100M graphics in my notebook and get acceptable results at medium settings. It is okay for me, because my notebook is a platform for serious development and not for serious flying.
So all things considered, the "optimum" X-Plane machine will have to be desktop computer, unless you like notebooks that are too heavy to carry, too big to rest on your lap and run out of battery quickly.
So, a desktop then. Where to start?
2. The case
Lets start with the obvious thing. A good case should
-fit a full sized ATX-mainboard
-fit a 28cm long graphics card without the need to remove the harddrive cage
-fit all drives (harddrives, SSDs, DVDs, BDs) you want
-have vibration-dampening fittings for hard disks
-have at least two 120mm fans
-have dust filters for the fans
Especially the graphics card colliding with the harddrive cage is an Achilles' heel of most cases. The best thing is to have a case with the hard drives mounted in a ninety-degree angle to the front, that is the hard disks slide in from the side. That makes plugging easier and leaves more space for the long graphic boards.
From the cases I came in contact with in the last three years (about 15 different models), my personal favorite is clearly the Lian-Li PC60-FN. I've never seen anything else so carefully thought out and well designed in this price range. It has an incredibly clever concept for hard disk dampening and mounting, fits a long 5850 graphics card with ease and is built entirely of aluminum.
A word considering "dampened" cases - personally, I don't like them. It's better to stop noise where it starts, than to glue a lot of dampening material to the walls. These material negatively effect heat dissipation. If you have the choice between investing into a dampened case and investing into quieter cooling fans, go for the fans.
Ah, the fans. There should be two of them, one mounted directly in front of the hard disks, blowing cool air from outside over the disks, the other on the top of the back wall, blowing the air out of the case. Hard disk life is greatly improved by cooler temperatures.
The fans should be 120mm in diameter or more. The more diameter, the less RPM is required to move enough air. RPM means noise. 'Nuff said.
If your case already comes with fans (some of them do, the PC60-FN also), fine. If not, Pabst is the manufacturer of choice.
3. The power supply
How might the power supply affect my flying experience?, you may ask. Well, the power supply affects overall system stability. If the PSU can't handle sudden surges in load when CPU and GPU change clock rates, there will be voltage drops that lead to microstutters at best and to blue screens of death at worst.
There has been much ado about the "watts" the PSU can deliver, and this has been greatly exaggerated in the past, leading to 1kW PSUs. More meaningful is the stability of the power delivery. As a general rule of thumb, if you are offered a 600W PSU at $X, and a 1000W PSU at $X-10, go for the 600W.
A good power supply should have two separate 12V lines, an active Power Factor Correction and have the 80+ efficiency label. The point of the efficiency label is not that you can save lots of money on your power bill (I calculated it some time ago, and found out that going for a 90% PSU would save me the equivalent of 1.5 pizzas per year) but that it indicates a good manufacturing.
Wether you go for BeQuiet!, Sharkoon or Seasonic is up to you. I personally like the german-engineered (but chinese built, like all others 
) PSUs from BeQuiet a lot, but the name doesn't really matter. As long as you dont fall prey to the "more watts per dollar" myth, you should be okay.
So how much "watts" are really required? That depends if you want to go for two or three graphics cards. The GPUs are the biggest power consumer in your PC. With the usual single-card setup, 600 are certainly enough. Only if you want to drive 4 or more displays with more GPUs, you should look in the 750 to 1000 range
4. The mainboard
While the choice of mainboard influenced your "benchmarkable" performance in bygone days, this is not true anymore. Wether you go for a $60 or a $300 mainboard, it does not affect your frames/sec, but again is a matter of the overall stability. Cheap mainboards use cheap capacitors and cheap voltage regulator chips. Cheap capacitors dry out after a year or two and lead to malfunctions (Blue screen of death). Cheap voltage regulators often make the "whining" noise when the CPU adjusts the voltage. Modern CPUs change the core voltage thousands of times a second (as they change the clock ratio with load) and with cheap voltage regulators, you hear this and it drives you crazy. Good mainboards advertise their 6 or 8 or 10 or even "16+2" phase "power control design" as the ultimate "green energy saver". That's not the point. Again, it will save you about a soft drink a year on your power bill, but it is good manufacturing, good capacitors, and silent voltage regulators.
Apart from this, you should have a look at the overall layout (are there any expansion cards you need to keep from your old PC, are there enough PCI slots), look that ATA 6G is supported, and that either USB 3.0 or e-SATA ports are available. You will never want to put your backup again on a USB2.0 external hard disk if you ever used eSATA, trust me.
The manufacturers recommended are ASUS, Gigabyte or MSI. I liked the Gigabyte boards, but suffered three catastrophic failures in a row in 2007. I switched to ASUS then, and have an unprecedented stability record with the upper-class ASUS boards until now. Perhaps Gigabyte has improved its Q.A. now (press indicates so), but I can not comment on that, since I decided to not go for Gigabyte anymore.
5. The CPU and cooling
In this section i have little to add to my original recommendation. A decent CPU is always priority #1. Don't bother going for a $500 graphics card and a cheap CPU. Might be okay for most of the games out there, not for the flightsims. This applies to both X-Plane and MSFS.
The CPU of choice these days is the i7-2600K (note the K, which indicates a free clock multiplier). These CPUs have an incredibly large margin for OC, there is no need to invest in the expensive -2820s or "Extreme Edition". Almost every 2600K can be OCed to 4GHz without problems. Invest some $50 in a decent aftermarket CPU cooler and throw away the thing that intel ships with the CPU. I can recommend the "Alpenföhn Brocken" (again, German designed, Chinese made), it is fairly easy to install, super-silent and shows great results with moderate OC. Other good manufacturers are certainly Scythe and Thermalright. If you are going for agressive OC, then and only then you should deign water cooling a look. But a water cooled CPU for every-day use, even if moderately OC'ed, is nonsense. You should steer clear of the "all-in-one" water cooling sets out there. The hose coupling are certainly subject to small leakages over time, and this can render your PC totally worthless in blink of an eye. So unless you know exactly what you are doing, go for a decent air cooling.
6. RAM
Also, little to add to my original recommendation. 4 Gig is absolute minimum, and in combination with an i7 CPU with triple channel, it should be 6 Gig. Whether you go for Corsair, OCZ, G.Skill or G.E.I.L is up to your personal preferences. I had no RAM failures in the last three years with either of them. I suffered RAM failure with Infineon RAMs in the past.
Before you install the OS on your PC, let it do a RAM check overnight. Will save you lots of trouble when you discover a faulty RAM early, then when you hit the Blue screen of Death in final approach after a cross-the-pond. Goldmemory or Memtest86 are the tools of choice. Also, almost every CD-bootable Linux these days comes with a Memtest boot option, which usually boots Memtest86.
7. GPU
First question: How many of them? Neither X-Plane nor MSFS gains any power from SLI or crossfire, neither X-P nor MSFS uses PhysX, so there is no need for a installing two GPU boards if you want to feed one or two (or three, via triplehead) monitors. Only if you have to drive more displays, you need a second card.
It goes without saying that X-P will not gain anything from a dual-GPU on one board graphics card. If you play Crisis when not flying X-Plane, okay, go for it, but otherwise save the money.
I have nothing to add to my original opinion on nVidia vs ATI:
I still prefer nVidia over ATI cards even today. The ATIs are currently on the bleeding edge of technology and nvidia is a bit behind. That's true. But nVidia's drivers a far superior to the ATI ones. Much less fiddling required to get everything look "just right". Also, ATIs driver situation on Linux is ridiculous. I use Linux as my primary X-Plane platform and get outstanding results with the newest nvidia drivers. On MAC, the situation is exactly inverse, the nvidia drivers for Mac are a bad joke. Only there I would go for ATI.
So in summary: For Mac ATI, for Linux nVidia. For Windows only environments, the ATI 6950 might be an option, offering more power at less noise and less heat than the GTX570 at a cheaper price. I'm not a neutral adviser here, because I use Linux as my primary platform, so ATI is never in my research of the "best choice". But the better driver remains true also on Windows. Less fuss, at the cost of more heat, more noise, and more money. Up to you to decide whether you go for ATI 6950 or nVidia GTX570.
What might be a good deal however, is the GTX560Ti from nVidia, which suits also a smaller budget, but also fulfills the requirements of X-Plane 10 (Shader Model 5). But be very sure to get a GTX560 Ti and not the GTX560 Ti (OEM), which is a downsized version with less shader units.
8. Hard disks and SSDs
The only thing that didn't speed up over the past five years are our hard disks. CPUs and GPUs have become incredibly faster, but HDDs remain slow even today. That being said it is not a question if an SSD is a good choice, but how big it shall be. You can answer this question yourself, open your file manager and look up the size of your X-Plane installation, the size of your OS, add them, and add a 25% margin. If you are one of those "I install every scenery all over the world no matter if I ever fly there", I have bad news for you. An SSD suiting a full-fledged X-Plane and Windows (at least 25Gigabyte for a decent Win7 64bit installation these days) costs a small fortune. See below for an alternative. The 25% margin is by all means necessary for performance. This is due how to the SSD controllers arrange the write-accesses to the memory, and if they can't find enough blocks in a row, IO-performance greatly degrades. Also remember that de-fragmentation is deadly for SSDs.
So, a reasonable X-Plane installation with only the scenery installed where you actually fly will fit nicely on a 120Gig SSD from the Intel 320 series. The Intels are currently the only ones to use the fast SLC memory, in contrast to the slower MLC. So if you are going for an SSD, nothing beats an Intel 320.
It goes without saying that you don't want to put all your Downloads, Music and stuff on the SSD, but on a separate hard disk. Here you can simply go "bigger is better", because speed doesn't matter anymore for your system performance. Wether you choose Western Digital, Seagate or Samsung is up to you. I had two catastrophic failures with IBM/Hitachi disks shortly after each other in 2006 and decided to not buy any disk from IBM/Hitachi ever again. From what I have heard from a friend who worked in data recovery, Samsungs are the most reliable disks out there and IBM hasn't become any better until now.
So you absolutely need your 100GB X-Plane install with all sceneries from Timbuktu and Spratly Islands? Well, there is the VelociRaptor disk from Western Digital. It's a disk originally from the server business, tuned for optimum speed. It is loud, expensive, and not as fast as an SSD, but at its size of 150GB considerably cheaper than an SLC SSD the same size.
What about a RAID, you may ask. A RAID is only good with a dedicated RAID controller, a separate PCI-Express card that offers a real controller. Software-RAID is useless in terms of speed, because it puts load on the CPU. The RAID-controllers on the mainboards can do the job, but it is dangerous. It goes without saying that a RAID 0 must be backed up externally, since you double the probability of a hard drive failure. But also a RAID 5 or 6 is a dangerous thing without a dedicated controller, because the RAID depends entirely on the controller, its firmware, and its settings. Chances are that you suffer a mainboard failure, all your data on your disks is perfectly okay, but you don't get a replacement mainboard with exactly the same controller, firmware and setup. Then say farewell to your data on the healthy hard disks. This is less a problem with an industry-grade dedicated RAID controller, but these are expensive.
A word to backups, if I may.
I have met people who say "I never to backups, I have a RAID 1/5/6/JBOD, whatever". RAID protects you against a drive failure, but not against voltage surges, PSU failures, fire, water, theft and plain stupidity. And RAID 5/6 is dangerous because people get lazy: "Oh, the hard disk failed. Well, the two others are doing well, I'll buy a new one when I have time..." Chances are, that when you are running a RAID of hard disks from the same manufacturer you bought at the same time, they are going to fail at about the same time. Again, saionara data. Data recovery from failed RAIDs is immensely complicated and costs several thousand Dollars.
If you want to protect your data, make backups on an external hard drive, and store this drive as far away from your computer as possible. If you have really critical data, save the backup on an encrypted volume and give it to one of your friends to store it for you.
An external e-SATA or UDB3.0 HDD is a must.
9. Sound
Do I need a dedicated sound chip? For most purposes, no. X-Plane's sound is a joke compared to the surround sound of FSX, sorry to say that. I have two sound cards in my PC for the simple reason of a more realistic online flying experience. I put the sim sound through one sound chip to my stereo, to get the right "big roaring engine" sound as the background, and use the other sound chip tied to my headset for VATSIM. Of course, this is gross overkill since you can achieve the same result when using a USB headset (headset with integrated audio chip) and X-Plane doesn't draw any benefit from a dedicated sound chip. If I hadn't been into audio-editing before, the sound chip of the mainboard would do.
10. The OS
Whether you go for Linux or Windows is a choice of your personal preferences. But a 64bit OS is mandatory today. I've been using 64bit Linux for years now, the troublesome era of compatibility nightmares is over now, same applies to Windows 7 x64 these days. 6 useable Gigabytes of RAM are great for doing number-crunching jobs like videos or audio editing. If you're not relying on stoneage scanners or tape drives without 64bit drivers, there is no need to stick to 32bit a OS.
When you go for Windows, 7 is the system of choice. Who worked with 7 for a day, doesn't want to use XP or Vista ever again.
I personally like to be in control of everything, and that is why my OS of choice is Linux. I had Suse, Mandriva and Ubuntu in the past and got stuck with Suse. For the beginner Ubuntu is of course the system of choice, since you get a lot of community support for it. I personally go for Suse because of the great KDE Integration.
11. The network, internet and security
I have nothing to add to what I wrote before:
Internet connection is a must. Far too many applications require internet access. Do you really want to download your weather on one PC and drag the METAR file to the other on a USB drive? How to pull in weather updates on long haul flights w/o internet connection?
You should definitely use a home router with stateful deep packet inspection and NAT. I think most people use these today, but those who don't are the reason we still have so much zombie PCs sending all the spam.
If you have a rouer, you should forget all the "Personal Firewall" and "Security Suite" stuff that is sold for Windows PCs. It's totally useless at best, certainly impairs I/O-performance and makes your PC a nightmare to administrate at worst.
You don't need a firewall behind a router. period.
On Windows, install Microsoft Security Essentials and be done with it. It's free, and you come in contact with it only once during the lifetime of your windows installation. And that is when you install it. It's the AV with the absolute minimum "annoyment" potential these days. It's just there and doesn't bother you at all. IMO the best invention from Microsoft for years now.
What you should do nevertheless, is to exclude your X-Plane directory from the AV guard and scanner scope. That will increase I/O-performance, while posing no additonal risk. You don't normally extract stuff downloaded from the Internet directly into your X-Plane dir, you usually unpack it to some temporary folder, don't you? When you do, the AV guard will have scanned all this already, and there is no need to scan every file loaded by X-Plane every time.
Okay, time for a break now. This is all I can think of right now, I certainly missed some points and certainly some of my propositions are questionable. So comments are highly welcome.
Philipp