In this story ...Hardware Tips: Find the Perfect Hard Disk for Your PCFast Monitor Resets

But not every PC can accommodate today's ATA (EIDE) hard drives. Some drives may have more storage capacity than your PC can recognize, some may be too fast for your system, and some may not fit in your PC's case. Before you buy the latest drive, make sure your PC can use it.

Hard disks with double-digit-gigabyte capacities are no problem for most PCs purchased in the last three years. But older systems have drive-capacity limitations. Here are common size limits, and how you can get around them.

8.4GB: Systems with a BIOS date before 1998 typically don't support drives with capacities greater than 8.4GB. If your BIOS doesn't support large-capacity drives, see if your PC vendor's Web site offers a BIOS update for your machine.

If you install a drive with a capacity of 8.4GB or greater and your PC fails to recognize its full capacity (and you can't find a BIOS update), you can bypass the BIOS and the onboard disk controller by installing an updated ATA disk controller card such as the $34 Ultra100TX2 from Promise Technology (800/888-0245). To view your drive's capacity, open My Computer, right-click your hard disk, and select Properties. A graph shows the drive's capacity, the storage space in use, and the amount available (see FIGURE 1).

4.2GB or 3.2GB: Some PCs manufactured before 1998 have BIOSs that limit disks to one of these two capacities. To remedy this, either get a BIOS upgrade or buy a new disk controller card.

2GB: Any hard drive using the FAT16 file system can recognize only up to 2GB. This includes systems running Windows 3. x and the original version of Windows 95. If you have an old FAT16 drive in a PC using Windows 95B or Windows 98, you can upgrade the disk to FAT32 using the Windows FAT32 Drive Converter Utility. You cannot use any disk utilities designed for FAT16 drives after making the switch, but your 16-bit applications will run just fine.

A drive with the latest version of the ATA data transfer technology--currently the Ultra DMA/100 mode (also called Ultra ATA/100)--will work at top data transfer speeds only in PCs with the latest chip sets. Most PCs made since 1999 support the previous Ultra DMA/33 mode, and many support Ultra DMA/66 mode. To find out which mode your PC supports, check your system's documentation or visit your PC manufacturer's Web site.

There are six ATA standards (ATA-1 through ATA-6) and often several modes for each. Manufacturers have assigned their own names to some modes--sometimes to denote added capabilities. FIGURE 2 provides some ATA perspective.

Your new hard drive's ATA mode does not have to match that of your PC. The latest drives will operate at the fastest mode your PC supports. Unless you often move huge files, a lower mode won't cut performance much. Still, save money and buy a drive that matches your PC's capabilities.

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