[Answered] Why did Microsoft limit FAT32 format to 32GB only?

Discussion in 'Windows XP / Older OS' started by Ocygord, Jan 18, 2018.

  1. Ocygord

    Ocygord MDL Member

    May 26, 2011
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    Looking back I am wondering why did Microsoft limit FAT32 drives format tool to only support up to 32GB. According to the docs, these can support drives up to 16TB and supports partitions up to 2TB, so why this limit?
    Windows XP is such an example, on the setup screen, any drive over 32GB will be formatted as NTFS. I never understood it.
    Thank you..
     
  2. Michaela Joy

    Michaela Joy MDL Crazy Lady

    Jul 26, 2012
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  3. John Sutherland

    John Sutherland MDL Senior Member

    Oct 15, 2014
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    Hello @Ocygord - Your question made me dig out my copy of "Using Windows 98 Second Edition" and re-read Chapter 9 - Working with Disks and Drives. Part of the problem with FAT32 is that as the partition size increases, so does the size of the individual clusters in the filesystem. From a table in the book, with the third column added by me:

    Partition Size ----- Cluster Size ------ Number of Disk Sectors (512 bytes/sector)

    <260MB ------------- 512 bytes -------- 1
    260MB - 8GB ----- 4KB ----------------- 8
    8GB - 16GB -------- 8KB ---------------- 16
    16GB - 32GB ------ 16KB -------------- 32
    >32GB ---------------- 32KB -------------- 64

    Now, an example from the book: Suppose you have a FAT32 partition greater than 32GB in size, and need to write a 100KB file to disk. At 32KB per cluster, you would need four clusters. The first three would be 100% full, containing a total of 96KB. But the fourth would only contain 4KB, and the remaining 28KB in that particular cluster is wasted, since it is allocated to that file and you cannot write any additional data to it. This is what is called "slack space" on the disk.

    In this example, we're only talking about one very small file. But multiply that by thousands upon thousands of files, and this slack space can add up quickly on FAT32. According to the book, anywhere from 33% to 66% of the space on a FAT32 partition can be wasted depending on how many small files are present.

    In contrast, the cluster size used by the NTFS filesystem is 4KB, regardless of the size of the partition. The same 100KB file would neatly fit on 25 clusters on a NTFS partition, with no wasted space. So I think part of Microsoft's reasoning for the FAT32 partition size limit of 32GB is to limit just how much disk space you can potentially waste by using it, and encourage you to use the more efficient NTFS filesystem on large capacity disk drives.

    Reading through that book brings back memories. The one thing I remember about using FAT32 was that once you had defragmented the Windows C:\ system partition, it stayed defragmented for quite a while.
     
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  4. Ocygord

    Ocygord MDL Member

    May 26, 2011
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    @John Sutherland
    This is a very interesting find, John. It certainly explains the why .
    Thank you!
     
  5. Ocygord

    Ocygord MDL Member

    May 26, 2011
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    @John Sutherland
    Do you by any chance have Using Windows 98 Second Edition in electronic form (pdf, etc.) ? If so, could you upload it somewhere? I collect old windows manuals, and I would really love to have that if you are willing to share.
     
  6. John Sutherland

    John Sutherland MDL Senior Member

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    #6 John Sutherland, Jan 19, 2018
    Last edited: Jan 19, 2018
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