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Issue #431: October 25–31, 2015

Q: From time to time, my computer freezes and I get a blue screen that says “Bad Pool Header” – computer does a restart after a few minutes and then it seems to work fine. What causes this and how do I correct?

– Jerry G.
Niceville, Florida

A: Oh my. Don’t you just absolutely love the cryptic error messages that Windows throws at you? I mean, your PC might as well have a “Check CPU” light somewhere on the case, as hardly anybody understands these errors. As I’ve said in the past, it’s almost as if Microsoft expects everyone who uses their products to have an advanced degree in computer science. Well, Jerry, I don’t expect that of you. So, let’s start as we so often do, with learning a little more about the problem, then I’ll see if I can point you in the direction of a solution. (Caution – extremely Geeky content ahead!)

The “pool” in question is the pool of memory that the kernel (the operating system core) controls. Now, at the basic hardware level, memory is allocated in units called pages, each of which consists of 4096 bytes. This size is generally too small to be useful to most device drivers, and even for the kernel itself. For efficiency, the kernel allocates many pages at a time well before they are needed, and it groups these large blocks together into a pool. This memory is then farmed out to system processes that request it. Each of these allocated hunks of memory has a small set of data attached to it called the POOL_HEADER which helps the kernel to keep track of the size of the memory block and the process to which it was allocated. When you get the message BAD_POOL_HEADER, it means that the kernel encountered something in one of these headers that it did not expect. On the surface, it appears that the problem lies with the kernel, since the error says that the POOL_HEADER is “bad”. Well, that’s not necessarily the case. The POOL_HEADER might be just fine, but some process is sending bad information to the kernel when trying to access the memory. The kernel (read: some engineer at Microsoft) chooses to call this mismatch a “BAD_POOL_HEADER”, leaving you and many other people scratching your head, and wondering what went wrong, and how to fix it.

When a computer has been running fine, and suddenly exhibits this problem, it can almost always be traced to some change that was recently performed to the system. Something like a new piece of hardware (which causes new driver software to be installed), new software, such as a new or different or updated virus scanner, or a new operating system, such as an upgrade to Windows 10. My advice to you is to take a good close look at your hardware drivers first, bearing in mind that there are drivers for everything, including things that you might not think of, such as your touchpad, built-in magnetic and optical storage devices, USB devices (including built-in USB bus controllers) and much more. If you’ve recently updated to Win10, it’s possible one of your drivers isn’t fully compatible. I gave this advice in a recent column, and it is just as applicable to you: Make a visit to your computer vendor’s website and search for updated drivers. Install anything that’s newer than what’s currently installed. Then visit the Microsoft Update website and download any updated drivers and Windows updates. Hope this wasn’t too geeky for you! Good luck, and happy computing!

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