Determine OS Block Size

1. Windows Machine
If you use ntfs file system you can use fsutil fsinfo ntfsinfo drivename:  to get information of block size.

c:>fsutil fsinfo ntfsinfo f:
Microsoft Windows XP [Version 5.1.2600]
(C) Copyright 1985-2001 Microsoft Corp.
C:Documents and SettingsAdministrator>fsutil fsinfo ntfsinfo D:
NTFS Volume Serial Number : 0xc054aec854aec090
Version : 3.1
Number Sectors : 0x000000000c34f28c
Total Clusters : 0x0000000001869e51
Free Clusters : 0x00000000015f0419
Total Reserved : 0x0000000000000000
Bytes Per Sector : 512
Bytes Per Cluster : 4096
Bytes Per FileRecord Segment : 1024
Clusters Per FileRecord Segment : 0
Mft Valid Data Length : 0x0000000003528000
Mft Start Lcn : 0x00000000000c0000
Mft2 Start Lcn : 0x0000000000c34f28
Mft Zone Start : 0x00000000000c3520
Mft Zone End : 0x00000000003cd3e0
C:Documents and SettingsAdministrator>