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October 26, 1998

FAT-32X may operate differently than FAT-32 on large hard drives

Last week, I wrote that Gibson Research's SpinRite 5.0 can correct hard disk errors that prevent you from converting a Windows 98 drive to the more efficient FAT-32 file system.

This week, I'd like to add some information about FAT-32 that has arisen as people start taking advantage of the new file system's capability to support larger and larger drives.

First, a review: Windows 95 and older PC operating systems used a file allocation table called FAT-16. FAT-16 allowed hard drives to be as large as 2GB. As drives reached this size, however, FAT-16 became an inefficient way to store files. On a drive larger than 1GB, a FAT-16 drive consumes a 32KB cluster merely to store a single small file -- even a 1-byte file.

The FAT-32 file system uses 4KB clusters on drives as large as 8GB. This reduces cluster waste. Converting a FAT-16 drive to FAT-32 can give you back approximately 20 percent of your hard disk space.

If you have the Windows 98 CD-ROM, you can find out exactly how much wasted space you would regain in the conversion of a hard drive to FAT-32 by running a Microsoft utility called Fat32win.exe. This utility is found in the D:\Tools\Reskit\Config folder, where D: is the drive letter of your CD-ROM drive.

FAT-32 was introduced with Windows 95B. Win95B provided no way to convert a drive to FAT-32 except repartitioning an entire drive, thereby erasing all its data. Windows 98 provides a convenient conversion utility, although it does not provide a way to convert a FAT-32 drive back to FAT-16.

As I stated last week, you convert a Windows 98 drive to FAT-32 by clicking Start, Programs, Accessories, System Tools, Drive Converter. There are a couple of cases in which you shouldn't convert. First, FAT-32 drives cannot currently be compressed with Microsoft DriveSpace, and a compressed drive cannot currently be converted to FAT-32. Second, some laptops with "suspend" features won't resume properly if FAT-32 is the file system used by the boot drive. The FAT-32 converter warns you if either of these cases is present when you try to convert.

Another situation has arisen, now that hard drives are getting larger and larger. Some new PCs come from the factory with hard drives larger than 8GB, partitioned as a single large drive letter, namely C:.

On a FAT-32 hard drive larger than 8GB, Microsoft uses what is called FAT-32X ("X" as in "extended"). A FAT-32X partition supports hard drives with more than 1,024 cylinders, the maximum number supported by many PCs' BIOS routines.

Disk utilities are just beginning to adapt to FAT-32X partitions. For example, Version 4.0 of PartitionMagic, the premium third-party partitioning software, was just released last month by Orem, Utah-based PowerQuest to support FAT-32X drives. PartitionMagic supports conversions both ways between FAT-32 and FAT-16. It also includes a BootMagic utility to allow a single drive to multiboot between Windows, Windows NT, Linux, etc. For more information, see

Microsoft cites another potential limitation on FAT-32X drives. Although FAT-32X supports drives as large as 2 terabytes, according to Knowledge Base document Q154997, the boot partition may not be larger than 7.8GB due to the hardware limitations of Interrupt 13. This would seem to restrict us to 7.8GB C: drives at present. I hope to have more information about this from Microsoft in an upcoming column.

Brian Livingston's latest book is Windows 98 Secrets (IDG Books). Send tips to He regrets that he cannot answer individual questions.

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