As an experienced tech, I cringe when a user complains of a slow PC. Problems that can slow down a computer are so numerous that you can troubleshoot ’til the cows come home and never find the cause. Such PC speed killers include: incorrectly configured antivirus software, low memory, too many background services running, a fragmented hard disk, or network congestion—and these are just the well-known problems.

But when you’ve checked for common problems and the PC is still slow, where do you look next? The problem could lie in one of these five less commonly checked areas.

Shorted patch cable
If a patch cable has a short, it has an unreliable connection to the network. A PC with an unreliable network connection will usually have a lot of retries when sending and receiving data. This makes the send/receive process take considerably longer than normal.

How much a short slows down a PC really depends on how bad the short is and how heavily the user works from the network. A very mild short might not be noticeable without test equipment, but a bad short could make the PC almost unusable. A shorted patch cable is most noticeable when a PC loads applications from a network server.

Low virtual memory
When a PC gets low on memory, Windows relies on a process called paging to move a page of memory (not currently being used) from physical RAM to a swap file (virtual memory). The page is stored in the swap file until it’s needed again, at which time the page is moved back to the physical RAM.

Not every memory page can be swapped, though. Some pages that contain critical operating system data must remain in RAM. Likewise, some RAM is consumed by the swapping process itself. This means that at any given time, less memory is available for data than you might think. Although swapping is a normal process, excessive swapping—called thrashing—is a big problem. Thrashing occurs when data is constantly moved between RAM and virtual memory. The biggest symptom of thrashing is that the PC runs very slowly and the hard disk is constantly running. The best way to stop thrashing is to simply add more memory to the PC.

My computer room has about 16 computers in it, and these machines give off a lot of heat. While I’ve never done any benchmarking to prove this, I’ve noticed that on the days when the room is excessively hot, the computers run more slowly. It never seems to fail that as the room cools down, the computers begin to run at normal speeds. For more information on keeping your PC cool, check out this article by James McPherson.

Improperly configured BIOS
Although there are many BIOS settings that can affect performance, some BIOS versions contain the setting Memory Hole. When Memory Hole is enabled, the machine deactivates all but the first 16 MB of RAM. This means that even if the machine has a full gigabyte of memory, only the first 16 MB will be accessible to the operating system. Less memory means more swapping and thus slower performance. To determine if your BIOS has the Memory Hole setting, check the manufacturer’s Web site or the documentation that came with the motherboard.

Generic system board drivers
Most computers come with a driver disk for the system board. This driver disk contains system board specific drivers and usually custom drivers for your hard disk controller. If you have a name-brand computer, such as Dell or Gateway, you can be reasonably sure that this disk was loaded at the factory. However, if you have a generic PC or if you installed Windows yourself, this disk may have never been loaded.

I personally always scoffed at the system board driver disk, assuming that it was unnecessary since Windows had its own set of drivers. However, a couple of weeks ago, I absolutely couldn’t get a particular application to run for more than a couple of minutes without producing the Blue Screen of Death. I called the application’s tech support department and was told to load my system board drivers. After doing so, not only did the Blue Screens go away, but the machine’s performance also improved.