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GPU FAQ

09:54:14 30.05.2012 posted by Passcape_Admin at 09:54:14 30.05.2012

Q: What are the system requirements to run GPU recovery?
A: NVidia video cards with CUDA compute capability 1.1 or higher. Even though older cards (based on CUDA 1.0) are supported as well, you will probably have to adjust some default settings to make them work correctly. The full list of CUDA supported devices is available here. Besides, you should also have the latest video drivers installed. In most cases, your GPU should have at least 256 Mb of video memory.
 
Q: How do I know which architecture does my video card support?
A: Launch Windows Password Recovery, open the menu 'Options - General Options,' select the 'GPU Settings' tab, and choose your video card here. The 'Compute capability' field in the description section should display your GPU architecture.
 
Q: Where can I download the latest video drivers?
A: You can get the latest drivers from NVidia web site.
 
Q: Where can I read more info about CUDA?
A: Wikipedia is a good starting point to start from.
 
Q: After I launch a GPU-based attack, my computer freezes or crashes into BSOD. What’s the problem? 
A: The problem may be caused by the following reasons:
  • Your video card had been overclocked, and it was malfunctioning at high load. If that’s the case, set the frequencies of the video memory/cores to its default values.
  • Insufficient or ineffective cooling of your card. When you launch a GPU-based attack, the program utilizes the most of the GPU power, and the GPU temperature rises to a critical level. Make sure that your video is well cooled, the GPU slot and your system unit are free from dirt and dust. An unwise use of some video settings may have a negative impact on the video card’s temperature and its stability under high load conditions. For example, some applications reduce the fan speed to minimize the noise, which does result in noise reduction, but also increases the temperature.
  • Power supply problem. Your card can consume a lot of energy at full load, and the power supply unit may be unable to handle such a high demand for power. If the video card has additional 6-pin or 8-pin power connectors, make sure they are all properly connected. 
 
Q: When I launch a GPU attack, my computer slows down a great deal. How can I fix that?
A: By default, the application is set up for using video cards of medium performance. That’s usually 256 threads per block, 256 blocks and 1000 passwords per thread. For older video cards such a configuration is too much and may cause a slowdown. Consider reducing the value of 'Passwords per thread' to 100 or even less.
 
Q: What's the best way to find optimal values of 'Thread blocks' and 'Passwords per thread' in the GPU attack settings?
A: Well, you can do that either empirically or by doing some maths. For example, if the values are 100 and 100, and the average speed of attack is 1 billion passwords per second, you can calculate that the GPU kernel is called about 390 times per second (the number of passwords calculated each time is usually 256 * ThreadBlocks * PasswordsPerThread). Naturally, the fewer calls, the less the overhead, and the higher the speed. On the other hand, you must call the GPU program at least a couple of times per second. So use a calculator, and adjust the parameters to optimal values. You can also adjust them using a rule of thumb, that is, increasing their values until the speed of attack stops going up and the computer slows down. If you have a GPU monitor installed in your system, it should indicate a load of at least 98-99 percent. Besides, it’s important to know some other things too. First, don’t set the summary values of those parameters too high. Otherwise your system may malfunction or freeze. Second, you’d better not set the value of 'Passwords per thread' at less than 100 as it will negatively affect the speed of attack regardless of what kind of video card is used.
 
Q: Does the PCI-Express bus have any impact on the performance?
A: Actually, this impact is negligible. It’s usually masked by other factors. So the generation of your PCI-Express bus and its performance don’t matter much.
 
Q: Does the amount of video memory matter?
A: No, it doesn’t. However, your GPU should have at least 256 Mb of video memory in most cases.
 
Q: What's the maximal number of GPU devices does your program support?
A: It depends on your hardware. Typically, up to 8 devices can be installed into a 4 PCI-E slot motherboard (4 double-GPU cards).
 
Q: A GPU-based attack slows down my PC so I can barely use it. How can I fix it?
A: There are two ways to fix it: temporary and permanent. As a temporary fix to the problem, open the attack settings and try reducing the number of GPU blocks used or the number of passwords checked per GPU thread. As a permanent fix, install a second video device, provided that you have a second slot on your motherboard and that your power supply unit can handle the additional load. For example, you can use some cheap card as the primary one (for displaying information on your monitor), and a second, more powerful one, for brute-forcing passwords.
 
Q: I have more than video cards in my PC. Can I use them all?
A: Yes. You can use all or some of them. Just open general settings and specify the GPU device(s) to be used by the program.
 
Q: Can I brute-force passwords on devices which performance varies a lot? Say, GT8600 and GTX580?
A: Yes, you can.
 
Q: Your application can’t use all of my GPUs.
A: You will have to disable SLI in order to be able to use all devices.
 
Q: The program can not detect my video card. What can I do?
A: Update your video drivers. If it didn't help, try to extend your desktop to all devices (if you have more than one device). Re-plug your device into another PCI-Express slot.
 
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