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Optimize IDE PIO Modes

IDE hard disks are accessed in one of two ways: programmed I/O (PIO) or direct memory access (DMA). The most common way is using PIO. There are 5 different PIO modes, from the slowest (0) to the fastest (4).

Most newer BIOSes support all of the different PIO modes, and will therefore support up to PIO mode 4 on the latest drives. The PIO mode should be set to the highest value that the drive can support; normally this happens automatically when the drive is autodetected, and most newer drives do support PIO mode 4. Some BIOSes may not set the drive to its maximum PIO mode, so you will want to check and adjust the mode to make sure it is set to the highest value the drive can handle. PIO modes are normally set using this BIOS setting, which is part of the group of settings available for each IDE device in the system.

Warning: You need to be careful when setting PIO modes, not to exceed the maximum level that the disk can handle. Many older drives can only go up to PIO mode 2, and some are limited to PIO mode 0. Furthermore, there is the issue of whether or not your system supports independent master/slave timing. If it does not, then both the master and slave drives (if both exist) on the IDE channel must run at the same PIO mode. You must make sure not to set the mode too high for one of the devices, even if the other one can handle it just fine.

Next: Optimize IDE Device Configuration

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