07-11
19

Data Recovery Techniques for Windows (7)

Cloudy Happy

Authoreric   Category Related Resource   Comments0   Post Time 2007-11-19 20:24:01 -0500

Calculating disk cluster size: A shortcut
If you're having trouble calculating cluster size, here's a shortcut. If you run CHKDSK against the volume that you are trying to recover (don't use the /F switch), one of the pieces of information that CHKDSK will give you is the number of bytes in each allocation unit. An allocation unit and a cluster are the exact same thing. Therefore the number of bytes in each allocation unit is the disk cluster size.

How long file names complicate data recovery
In the previous article in the series, we discussed how disks use clusters for storing files. Hopefully, you now understand how to determine how many clusters a file uses, because calculating the number of clusters in use will be critical when we actually go on to discussing data recovery.

Before we get to that point, we need to discuss another concept: long file names. A previous article explained that when you delete a file, the operating system replaces the first character of the file name with a sigma sign (or, on very old systems, a question mark). If we were still using the old eight dot three naming convention, that's really all you'd need to know about file names. However, long file names complicate things. It's important to understand how they're saved to a disk.

Why long files are names a big deal?
Why are long file names such a big deal? Because the FAT and the FAT-32 file systems don't natively support them. The FAT file system has been around since 1982. Back then, only the eight dot three naming convention was supported. When Windows 95 was released in 1995, the FAT file system was still the only file system available to Windows. (NTFS existed, but was not supported by Windows 95).

Microsoft wanted Windows 95 to support long file names, so it came up with a technique for retrofitting the FAT file system so that multiple directory entries could be used in conjunction with each other to store long file names. When Microsoft released OEM Service Release 2 (otherwise known as OSR2) of Windows 95, they introduced the FAT-32 file system. Although FAT-32 overcomes many of the limits of FAT, it is still an adaptation of the FAT file system rather than a completely new file system.

How long files names are stored to disk
With that in mind, let's take a look at how long file names are stored on a disk. When Windows stores a long file name on a FAT or FAT-32 partition, it must do so in a way that allows the file system to recognize the file outside of Windows. This may sound a little strange. But remember, despite what the marketing folks might tell you, all versions of Windows (except for the ones based on the NT Kernel) ride on top of DOS. This means that for those versions of Windows (3.x, 95, 98 and ME), DOS is the actual operating system and, technically, Windows is a platform. As such, files written to the drive must be readable from DOS, even though some versions of DOS do not support long file names.

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Tags Tags: Data Recovery,windows,data recovery,NTFS,ntfs,fat32

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