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Hard drives are transitioning from 512 byte to 4096 byte sector sizes, and it looks like Windows XP won't support these newer drives without additional software (such as WDalign from Western Digital)

My question is: how does this affect external hard drives? I'll be buying a 1TB USB external drive, and it'll be plugged into a mix of Windows 7 and XP machines. Is there an easy way to tell what the sector size on an external hard drive is?

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Please note that hard drive sector size != filesystem allocation unit (a.k.a "cluster") size as reported by the OS. NTFS, for example uses 4kB-sized allocation units but (on old HDDs) these are made up of 8 HDD sectors. en.wikipedia.org/wiki/Allocation_unit – sigint Mar 17 '10 at 8:49
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4 Answers

up vote 3 down vote accepted

Run wmic partition get BlockSize, StartingOffset, Name, Index from a Windows Command Prompt. The output looks like:

BlockSize  Index  Name                   StartingOffset
512        0      Disk #0, Partition #0  1048576
512        1      Disk #0, Partition #1  105906176
512        0      Disk #1, Partition #0  32256

Where block size is the drive's sector size. It unfortunately doesn't list the drive letter.

Also as I understand the article, the drive will still list that it has 512 byte sectors even though internally it uses 4kb sectors. So the only way may be to get the drive's spec sheet.

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The HDD may indeed misreport blocksize to the OS. However, if I try this on Win7 (which supports 4k sectors), it ought to report the correct blocksize. At least that way I can put a "don't use this on XP without WDAlign" sticker on the external hard drive. Any fellow commenters with 4k-sector drives, please chime in with your experiences. Thanks! – sigint Mar 18 '10 at 17:11
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up vote 1 down vote

You can do this via a command prompt. Open up CMD (Windows+r then type cmd) and run chkdsk driveletter: chkdsk c: It will be listed as x bytes in each allocation unit.

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I believe this talks about the file system, not the disk itself. – Joey Mar 17 '10 at 13:58
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up vote 1 down vote

I just verified this with WMIC on my windows XP box. This is the query: 

C:\>wmic DISKDRIVE get bytespersector, caption  
BytesPerSector  Caption  
512             WDC WD1600AAJS-60M0A0  
4096            TrekStor HDD USB Device

The newer Toshiba external disk is reported as 4096 bytes.

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up vote 0 down vote

You can examine the properties of a file on the disk (preferably a very small one) and it's "size on disk" can tell you the sector size. For instance, this 1 byte file consumes 4096 bytes on disk because 4096 is the sector size.

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This tells you the cluster size of the file system, nothing about the hard drive (except that the hard drive's sector size is probably a divisor of that). – Joey Mar 17 '10 at 13:28
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