Perhaps you've had this happen to you... You're wandering around and you open up a door to some random wasteland place and the game freezes. Music keeps playing.. All you can do it cntrl-alt-del and kill fallout3.exe from the task manager. Maybe you've tried editing your .ini file at the recommendation of another forum user but that didn't seem to help because now instead of freezing you're getting a CTD.

You're probably running Windows 7 too and you come here to find out that OS is not supported. Well believe it or not, FO3 runs perfectly fine under Windows 7.... Windows 7 isn't the problem. The problem is your CPU! No, there is nothing wrong with your CPU but there is something wrong with the way the game utilizes multiple threads and the way that ANY version of Windows assigns them to cores in the background. This causes the freezing. It will also happen in Vista and XP if you have more than 2 cores. Core 2 users will not experience the freeze (unless it's a Core 2 Quad) but Phenom X3 users and anybody else with multiple cores (or dual core CPUs with hyperthreading like Core i5s have) will get the freeze. This has been a known issue since the game came out and I think it even effects New Vegas (except it CTD instead of freezes)

Note this will only work if your OS shows 4 or more CPUs (virtual or physical, doesn't matter)

So try this,

Make a shortcut to FO3 by going to the games folder and right-clicking the exe file and selecting create shortcut. It will likely place it on your desktop which is fine. Right click the shortcut and select properties. Replace the 'target' with the following:

C:\Windows\System32\cmd.exe /C start /affinity 5 fallout3.exe

Now save it, maybe change the icon to the FO3 one.

What this does is limits the game to two physical cores. If you have hyperthreading, it will only use the actual physically seperate cores. You will still need to open up the fallout.ini file in your documents\games\fallout 3 folder and add iNumHWThreads=2 to the general section. Do not bother with any other ini 'tweaks' they only serve to hurt performance. For example, threadedai is set to 0 by default for a reason. Don't set it to 1, if it even does anything at all. And don't mess with the background load settings unless you want the game to stutter more when loading the world.

So there, not only have you tricked the game into thinking you only have 2 cores (which is perfectly fine performance-wise) but only two real cores will be assigned to the game so nothing Windows does in the background will cause it to crash. Is this a for sure fix? I dunno, hasn't crashed yet but that doesn't mean anything. This works for New Vegas if you want to try it there too but steam has to be closed before running the shortcut (otherwise it will load with the affinity set on all cores)

So why is everybody with Windows 7 reporting freezing? Because if you buy a new computer it comes with Windows 7, therefore everybody thinks it's a Windows 7 issue. If you go to google and search for "quad core fallout 3 freeze" you'll find tons of archived posts describing the very same thing in Vista and XP dating back to the game's release in 2008 so it is hardly new. We are unfortunately seeing it now that core i CPUs with 4 threads at the least are in the mainstream

Just an update, New Vegas must utilize multi core better. Verified with FRAPS that forcing New Vegas to use 2 cores caused reduced framerates and also bizarre framerate flucuation even when nothing goes on. Doesn't happen with FO3 though, just saying not to use this on NV. Maybe somebody will find a way (doubtful) to run FO3 using the NV executable. ha!

Yes you will all of which refer to the iNumHWThreads=2 fix in the ini and none of which have revealed this command line approach.

I'm currently testing this I can say that for the moment it seems to fix the freezing but I only tested for around 2 hours as I have a long day today, but for those of you that are using mods that are FOSE dependant you can set up the short cut with the target modified to
C:\Windows\System32\cmd.exe /C start /affinity 5 fose_loader.exe and it will load FOSE+Fallout under the same command line target.

While testing I removed all other ini tweaks except iNumHWThreads=2 and did not freeze but as stated there was only around 2 hours of hard testing so its not fully conclusive as yet, I did though with intention to see how far I could push it set all my graphics settings to ultra and other than occasional loading stutter this seems to be doing the job. I will state that you black screen on attempting to exit Fallout 3 and the process won't terminate properly, but I suppose thats better than freezing while playing FO3.

Big issue here is even gamesas tech support hasn't offered up that command line work around you've produced here. They've even linked me to multiple references on tweaks and possible fixes all of which revolve around the iNumHWThreads=2 in the ini, none of which have ever mentioned this command line work around.

So I'd think with Win 7 being a near to standard OS now for quite a lot of people these kinds of work arounds should probably be sticked at the top of the forum.

I will do further stress testing later as I get home but I did my usual full tilt run from Megaton all the way to Rivet City without a freeze based crash with all graphics settings cranked, largely the loading stutter, if this fix is actually "the fix" can easily be reduced by increasing preload memory limit and increasing cell buffers accordingly.

So we'll see. But as stated the whole "Google Search is your friend" thing is pretty obnoxious cause there are a lot of people trying to fix this problem and you seem to be the only person thats come across this little nugget thats brought it forward anywhere where it can be seen. Nearly all results in Google I found dealt with iNumHWThreads and bThreaded entries as attempts to cull the issue.

Sorry, I'll edit the OP, what I meant by "google search" is not to find a solution but to show that quad cores have been freezing under XP and Vista since 2008 meaning it isn't a Windows 7 issue. The problem is since many are using Windows 7 now and reporting it, the devs can just point to Windows 7 being the issue and using the fact that it isn't officially supported as a safety net. It's a problem that effects all quad core CPUs or any CPU where Windows shows more than two threads (like i5) and it's also a problem I suspect affects New Vegas.

FO3 runs fine on dual core CPUs. It does not run fine on dual core CPUs with hyper-threading like Intel i5s because they show 4 cores (2 are fake) and it doesn't run fine on Phenom X3s because they have 3 cores. It doesn't run fine on core 2 quads, i7s, x4s, etc because they have 4 or more cores (i7s have 8 cores, 4 real and 4 fake).

If you look at the CPU affinity in task manager after doing this command line short cut, it will show cpu o and cpu 2 checked off only. In a hyper-threading scenario, that means that only physical CPU 1 and 2 are in use by the game. On a triple, quad, etc it means the first and third are being used. Basically, the game should in theory run identical to the way it does on a dual core cpu

Couple of notes, If you have Windows installed on a drive other than C:\ then change the drive letter to the appropriate place where you have it installed

On Core i CPUs with turboboost, this will also allow the game to utilize turboboost more efficiently. I've never seen the affinity posted in relation to fallout 3 before but I have seen it for other apps that don't play nice with multiple cores or hyperthreading

This is not only a Quad Core issue as I am experiencing it under Win7 with my Ahtlon 64 X2 5200+. It always freezes when coming near the library in the Wastelands. Puting affinty (I think it's called in english) to only one (namely the second core because it has more "capacity" than the "main" core) using ctrl-alt-del solved the problem. Also choosing low quality textures solved it but I didn't want to play with low quality textures cause it looks awful

Can this be done in XP? I have an X3 cpu with 3 cores but this doesn't launch the game for me.

I've personally never used a dual core AMD CPU so I wouldn't know. I do know that I played 50+ hours with no freezing using Windows 7 and a dual core Intel CPU. My problems only started when moving to a quad core

You can modify the shortcut to say affinity 1 instead of 5 and this way you don't have to alt-tab to task manager (alt-tabbing causes instability anyways)

Not sure, you can try it but do the following since XP hates spaces:
Make the shortcut, right-click and select properties then choose Target:

C:\Windows\System32\cmd.exe /c start “” /affinity 4 “fallout3.exe”

If Windows is installed elsewhere, change c:\ to the appropriate drive letter

The quotes are to get around XP not liking spaces for whatever reason

Never heard of the game refusing to run just because of a CPU though.. could be something else

No the game starts up fine normally, just using this command line doesn't launch it is what I meant. Still doesn't launch with the modified line. Maybe someone else knows how to set it up in XP hopefully.

On this is where I've sort of been hammering gamesas, FONV is optimized for multicore usage and I've had very little problem running it as compared to FO3, which is why I've been saying they need to patch backwards, into Fallout 3, the multi-core enhancement they added to FONV and thus they have two working major titles and not one that requires software manipulation that the average user may not be competent or comfortable attempting, and another that runs fine without any need for doing anything but adjusting graphics setting for system capability.

FONV almost never crashes on me, ever, I can run all around the Mojave doing whatever and CTD's are few and far between.

So far this forced CPU affinity command line target is appearing to address the issue with FO3, the only problem is of course attempting to terminate the process which ends up needing to be done at the task manager when you're ready to exit the game. Other than that this seems to do the job. I've updated my ticket with gamesas tech support to reflect this data and did confirm that without this command line parameter, even with iNumHWThreads=2 in the ini the game was still utilizing all four cores on my computer. With this command line it is definitely setting CPU affinity to only CPU 0 and CPU 2.

Unfortunately, I don't think they're going to do anything further with FO3 at this point...

I used the command line affinity switch with FO3 for over 6 hours now and no freezing. I might just be lucky so far cause every now and then this happens, but this might just be a 'fix' afterall

Well I was thinking this was the fix, it definitely forces a two core affinity on the executable. As compared to running Fallout3.exe straight or FOMM+FOSE Loader which without this command line, even with iNumHWThreads=2 in your ini still utilizes all cores of your CPU.

Problem is today while running the game for an extended period I started noticing that instead of freezing I was simply CTD'ing and once again it was around the 1.5GB area of memory footprint that my earlier findings indicated.

So this appears to stop the freezing but it doesn't appear to stop large memory footprint CTD's which still leads me to believe that using bPreemptivelyUnloadCells=1 is potentially a good idea as a addition to this to avoid that. As I was seeing fairly good results with that while the game was still using all four cores of my computer.

I'm also suspecting some problem mod installations may be part of my own personal problem and I'm going to clean install everything and Fomod install all packages to ensure thats not part of the problem because some of my crashes are occurring in regards to Pipboy Interface and I'm just using the standard Pipboy, not the Readius, only difference really is in DarNUI but DarNUI is stable but its possible some menu element I installed as part of another mod isn't so...going to see what thats about. But not all CTD's were interface based with the Pipboy some were just outright stuttering lag into a full CTD which to me is still indicative of a memory leak.

Regardless will continue to force two core usage with the new install and see if I can figure out additional things that can be added to this to try to make the CTD's stop.

I was able to find an app that allows you to set the affinity before launching the game, but sadly it didn't stop crashing for me. I was able to confirm that the game was using the cores I selected, and tried every combination I could even trying only one core.

The only way I can get consistent play without crashes is to run in windowed mode. Sometimes it still crashes but not as often.

This game and NV just don't work well on my hardware for some reason. Maybe next time I upgrade I will get lucky and the game will finally work. I never had crashes on my old computer which was a clawhammer 3700+ and gt6800. That setup could not run AA and HDR at the same time though and when it died I was looking forward to finally running this game at the detail level I wanted. While the game runs great on high settings now the crashing is a nagging issue I think can't be solved. Windowed mode is ok but I don't get as good of frame rates when running full screen.

It's really odd that as long as the game has been out that no one has found the root issue that cause so many of us problems.

If you're using mods, make sure you get the bin file to modify the exe so that it is large address aware (assuming you are using a 64-bit OS). It's probably running out of memory when it crashes. The vanilla no-mod install hovers around 1GB only of ram usage

I've tried the large address aware fix for the exe and have found that after about 20 - 30 minutes of play I start getting a lot of lag accessing corpse/container inventories for some reason. Will give it another shot now that I'm forcing it to run on two cores and see what happens.

I haven't put any more time in the game for any stability testing, but I did do a FRAPS test because I noticed some portions of the game were running with a less-than-ideal framerate. Turns out that running on all my cores does indeed improve performance by 15fps at some points which is significant. So I did a test... I tested affinity 3 (which on my i7 uses one core with hyperthreading for two total threads) and left the .ini at two hardware threads. The game runs very sluggish. I didn't try it on just one cpu only since at a minimum the game requires two cores. I tried it with affinity 55 which uses my four physical cores without hyperthreading. There was still a 5fps drop in framerate vs using all 8 of my threads. So in conclusion, you might want to put up with the freezing because despite what people have said the game is indeed using all cores! Afterall, task manager claims the game uses 40 threads.

Actually heres a zinger. I did a full fresh install yesterday, Fomod installed all mods I use for the cleanest installs possible, put together a new merged patch.

I'm forcing a two core assignment as previous. I'm using the large address aware enabler. I am not running the exe's in Vista compatibility mode they're just running straight up without a compatibility mode setting at all.

And I upgraded to 8GB of physical RAM yesterday just on the off chance that might help.

And guess what? I don't crash or freeze at all now. I played for like 10 hours straight without a single freeze or crash, ran all over the Capitol Wasteland and went and did the Pitt and everything, there are some frame rate issues and increasing cell buffers doesn't appear to help with that. That could be limiting the cores as you've stated.

I'm going to back this out a step at a time, taking off the core assignment and letting it just run all four cores and without iNumHWThreads=2 in the ini and see if the performance is the same.

If it does, then I'm going to have to stand on FO3 1.7.0.3 eating a lot more memory in Win 7 64 than it should be and on 4GB systems causing critical memory faults which result in the freeze, though I really believe its a combination of a lot of things, and the simple fix is to retroactively apply FONV's enhancements for Multicore and Win 7 to FO3.

I agree with you there, it's definitely a combination of things. I can tell you this though - the non GOTY edition with no DLC ran rock solid for 60+ hours of gameplay on my core 2 duo over a year and a half ago. On 64-bit Vista AND 64-bit Windows 7 (I upgraded it after it came out). I only started getting crashes after the DLC was installed usually around "hooks" like the ferry to point lookout or the UFO. Incidentally that's also where the console GOTYs crash the most. But this freezing thing started happening as soon as a I got a new PC with a quad core and I've tried every tweak in the book and decided when I play the game I'll just put up with the freezing.

So no matter what i have tried... The affinity thing or changing the ini NOTHING WORKS.. runnin GOTY on an Intel Core 2 Quad 3.4 GHZ(OverClocked) Nvidia GTX 260 4 GB Of ram (3gb Utilized) on XP Pro SP3

and all the affinity does is pops a very fast flash of a cmd window then closes instantly...

Had the same problem in XP. You can use Task Assign to set affinity before launching the game, but as discovered here it probably won't help. I have just gone back to a default ini only allowing archive invalidation, and playing in windowed mode as that's the only way the game stays somewhat stable for me. For purely testing purposes you can download Task Assign here http://www.xdowns.com/soft/download.asp?softid=19069 and see what your results are. Just run the program, add fallout 3 to it and set the processors you want to use. Keep the program open and launch the game and it should work.

Where should I send the bouquet of flowers? This is just what I needed to fix the freeze problem, and I'd have missed this if I'd tried to run the game a month ago, when I finally got it to install after a year's wait.( I DL'd FO3 over a year ago from D2D, and somehow screwed up the InstallShield program so much that I gave up, which wasn't all bad; My 7 yo granddaughter knows all of Minsk's phrases in Baldur's Gate, and finishing The Nameless One's tale was very satisfying. Plus, I'm retired, so I have lots of time, though no patience. hehe) It wasn't until I re-installed Vista x64 and replaced the faltering video card that Fallout 3 installed successfully, and I'd have given up before seeing your very easy to accomplish solution a month ago. ( As you can surmise from my InstallShield fiasco, I am an ignorant nitwit, computer-wise.)

Anyway, thanks so much for sharing this, and I sure hope more people are helped by this simple remedy.

Digital Storm :
Intel Core I7 Extreme Edition 980X 3.33 over clocked to 3.9 GHz
EVGA X58 Classified 3X SLI MB
ATI Radeon HD 5870 4GB (ASUS ARES Unlimited Power Edition GPU
12GB DDR3 1600MHz Corsair Dominator DHX
2x (256GB Corsair Solid State) HD's
Extreme Cooling: H20: Stage 5 Sub-Zero system

Clicking "NEW Game" Fallout 3 starts the "clock" and freezes my computer at the completion of one cycle.

I have up dated to version 1.7.

So anyone assist these very OLD (81 years) bones?

Many thanks,
drybones

Perhaps you've had this happen to you... You're wandering around and you open up a door to some random wasteland place and the game freezes. Music keeps playing.. All you can do it cntrl-alt-del and kill fallout3.exe from the task manager. Maybe you've tried editing your .ini file at the recommendation of another forum user but that didn't seem to help because now instead of freezing you're getting a CTD.

You're probably running Windows 7 too and you come here to find out that OS is not supported. Well believe it or not, FO3 runs perfectly fine under Windows 7.... Windows 7 isn't the problem. The problem is your CPU! No, there is nothing wrong with your CPU but there is something wrong with the way the game utilizes multiple threads and the way that ANY version of Windows assigns them to cores in the background. This causes the freezing. It will also happen in Vista and XP if you have more than 2 cores. Core 2 users will not experience the freeze (unless it's a Core 2 Quad) but Phenom X3 users and anybody else with multiple cores (or dual core CPUs with hyperthreading like Core i5s have) will get the freeze. This has been a known issue since the game came out and I think it even effects New Vegas (except it CTD instead of freezes)

Note this will only work if your OS shows 4 or more CPUs (virtual or physical, doesn't matter)

So try this,

Make a shortcut to FO3 by going to the games folder and right-clicking the exe file and selecting create shortcut. It will likely place it on your desktop which is fine. Right click the shortcut and select properties. Replace the 'target' with the following:

C:\Windows\System32\cmd.exe /C start /affinity 5 fallout3.exe

Now save it, maybe change the icon to the FO3 one.

What this does is limits the game to two physical cores. If you have hyperthreading, it will only use the actual physically seperate cores. You will still need to open up the fallout.ini file in your documents\games\fallout 3 folder and add iNumHWThreads=2 to the general section. Do not bother with any other ini 'tweaks' they only serve to hurt performance. For example, threadedai is set to 0 by default for a reason. Don't set it to 1, if it even does anything at all. And don't mess with the background load settings unless you want the game to stutter more when loading the world.

So there, not only have you tricked the game into thinking you only have 2 cores (which is perfectly fine performance-wise) but only two real cores will be assigned to the game so nothing Windows does in the background will cause it to crash. Is this a for sure fix? I dunno, hasn't crashed yet but that doesn't mean anything. This works for New Vegas if you want to try it there too but steam has to be closed before running the shortcut (otherwise it will load with the affinity set on all cores)

So why is everybody with Windows 7 reporting freezing? Because if you buy a new computer it comes with Windows 7, therefore everybody thinks it's a Windows 7 issue. If you go to google and search for "quad core fallout 3 freeze" you'll find tons of archived posts describing the very same thing in Vista and XP dating back to the game's release in 2008 so it is hardly new. We are unfortunately seeing it now that core i CPUs with 4 threads at the least are in the mainstream

Just an update, New Vegas must utilize multi core better. Verified with FRAPS that forcing New Vegas to use 2 cores caused reduced framerates and also bizarre framerate flucuation even when nothing goes on. Doesn't happen with FO3 though, just saying not to use this on NV. Maybe somebody will find a way (doubtful) to run FO3 using the NV executable. ha!