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PC Hardware in a Nutshell, 3rd Edition by Barbara Fritchman Thompson, Robert Bruce Thompson

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FDD Interface and Cabling

The FDD interface and power requirements are completely standardized, as follows:

Controller

PC-class systems used a separate FDD controller card. XT- and AT-class systems and some early 386s used a combination HDD/FDD controller card. Current systems use an embedded FDD controller. These controllers differ only in their maximum data rate, which determines the FDD types they support. Early controllers run at 250 Kb/s, which supports only 360 KB 5.25-inch FDDs and 720 KB 3.5-inch FDDs. Later controllers run at 500 Kb/s, which supports any standard FDD, or at 1 Mb/s, which is required for 2.88 MB 3.5-inch FDDs. Run BIOS Setup to determine which FDD types a given system supports.

Tip

If you must install a higher-capacity FDD than the controller supports—e.g., if you must salvage data from a hard drive in a system whose old 5.25-inch 360 KB FDD has failed and you have only a 3.5-inch HD FDD to replace it—you have two alternatives:

  • Remove or disable the onboard FDD controller, and replace it with a third-party FDD controller that supports the higher-capacity FDD.

  • Lie to the old system about what type of FDD you are installing. For example, install a 1.44 MB FDD, but tell the system that it is a 360 KB or 720 KB FDD. All FDDs run at 300 RPM, except 5.25-inch 1.2 MB FDDs, which run at 360 RPM. That means that any ED, HD, or DD 3.5-inch FDD can emulate any lower-capacity 3.5-inch drive, as well as the 5.25-inch 360 KB FDD. Use blank DD diskettes, and format them in ...

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