DiskPatch manual - DiskPatch and Windows Vista

A word about Microsoft Windows "Vista" (tm)

With the introduction of Microsoft Windows Vista (tm) the rules for creating partitions have changed a bit. This is something that end-users will probably never notice, but on disk Vista handles the creation of partitions differently from all previous versions of Windows (you can read more about this here, but this is not required reading). In short, Windows Vista uses different start- and end locations to define a partition, so the structures and sectors that DiskPatch looks for during a repair operation are found in different places. In practice this means that if DiskPatch would analyze a disk that was partitioned using Windows Vista, and DiskPatch's analyze logic would assume the disk was partitioned using a previous version of Windows, nothing would be found because DiskPatch would look in the wrong places. So, before an analysis is started you must tell DiskPatch which operating system was used to create the partitions that you wish to repair. When an operation is started that requires you to select which operating system created the partitions, the following menu option is displayed:

Select the appropriate option and press <enter>. You can press <escape> at this point to abort the operation.

Choose 'Megabyte aligned' if the partitions were created using Windows Vista.
Choose 'Cylinder aligned' if the partitions were created using a previous version of Windows, or any other Microsoft based Operating System.

If you're not entirely sure which one to choose, try 'Cylinder aligned' first. In this time where Vista is commonly installed as an upgrade over existing partitions (and simply does not yet have the install base that previous Windows versions have), cylinder aligned is your best bet. If the partition repair list is empty or incomplete, try 'Megabyte aligned'.

The only DiskPatch repair operation where the choice for Vista or earlier versions of Windows is of any importance, is a 'Partition Table rebuild'. All other operations (cloning, surface scanning, disk wiping, boot sector repair etc.) are not affected by the changes that were introduced in Windows Vista.

The difference between Vista created partitions and Pre-Vista created partitions.

First, a little background information.
all hard disks are made up of sectors. Each sector has a number, the first sector being number 0 (zero). So sector 10 is simply the 11th sector on the disk (start at 0!) and so on. This type of numbering is called LBA addressing. LBA stands for 'Logical Block Address', which in this case simply means that sectors can be found on the disk by counting from the start of the disk. A simple clean system.
In earlier days, when disks were smaller, an additional system was used to define a location on a disk: the CHS notation. CHS stands for Cylinder, Head and Sector. Mechanically speaking, hard disks contain platters and each platter has it's own set of read/write heads. If you'd put the heads in a certain position above the platters and perform a read operation on all the heads, you would have read a cross section of the disk. A stack of rings if you will, one ring for each platter. This would be called a cylinder. Each cylinder would be numbered, the first one being 0 (zero). The read/write heads are also numbered (again, the first one being 0), so you can use a cylinder number and a head number to find a specific location on the platters. Finally, each of the rings we've read earlier consist of a number of sectors, which also have a number (sector numbers start at 1, not 0). So a CHS address of 9-0-1 would translate into reading the sector at cylinder 9, head 0 and sector 1 (remember: cylinder and head starts at 0, sectors start at 1). The maximum number of sectors in a ring would be 63 (from 1 to 63), the maximum number of heads would be 255 (from 0 to 254) and cylinders could be any number, so as disks got bigger the number of cylinders grew and grew. Of course there were almost never any disks that actually had 255 heads, this number was selected because at the time they thought it would be more than enough to accommodate even the largest disks. Obviously they were wrong...
This CHS notation is still in use today, but only because of backwards compatibility reasons: most recent operating systems don't use these numbers anymore. Since disks these days are quite big, disk manufacturers almost always set the number of sectors per ring to 63 (the max possible value) and the number of heads per cylinder to 255 (again, the max possible value). If you'd make these numbers smaller you could get a huge number of cylinders so it makes sense to select the highest possible values for heads and sectors: bigger chunks are easier to manage. For this reason most modern day disks will tell you that they have 63 sectors per head and 255 heads per cylinder, even if in fact that's not the way the disk is made up.

So what does this have to do with partitions?
All Windows versions before Windows Vista used these CHS numbers to select the start- and end location for a partition: a partition would always start on the first sector of a head location, and the partition would always end at a cylinder end location. Example: let's say we have a disk that has 63 sectors per ring, 255 heads per cylinder and 1000 cylinders. A start location for a partition could be 0-1-1 (cylinder 0, head 1, the first sector) and an end location could be 74-254-63 (cylinder 74, head 254 and sector 63). In this example 254 is the highest possible head number and 63 is the highest possible sector number: if you continue to the next sector these values would roll back their starting values, and the cylinder number would increase by 1. That's why we call this type of location (head 254 and sector 63) a 'cylinder end location'.
For this reason a partition would never be the exact size that you selected: during creation a partition was stretched or shrunk to make sure the start- and end locations would be according to the rules as explained above.
If a partition is created according to these rules, a partition is 'CHS aligned'.
Windows Vista ignores the whole CHS nightmare and uses only LBA addressing, so Vista starts counting at sector 0 and simply sequentially counts onwards. A new formula is introduced to determine the start- and end locations for partitions: a start location is always a multiple of 2048, an end location is always a multiple of 2048 minus 1. Nice and simple. The number 2048 was selected for a reason: 1 sector contains 512 bytes so 2048 sectors is exactly 1 megabyte. So if you select to create a partition of x megabytes in Windows Vista, it will be exactly that size in megabytes.
If a partition is created according to these rules, a partition is 'megabyte aligned'.

And finally, what does all this have to do with DiskPatch?
DiskPatch uses a clever scheme to search the disk for partition remnants. As you can see from the explanation above, it's imperative that DiskPatch knows where to search. Therefore DiskPatch needs to know if the partitions were created using Windows Vista (so DiskPatch can look at LBA locations that are a multiple of 2048) or if the partitions were created using earlier versions of Windows (so DiskPatch can look at the correct CHS locations). If you would let DiskPatch scan a Vista disk in CHS mode it's likely that nothing would be found, so it's essential that you select the correct search method. Also, if DiskPatch accidentally finds stuff while using the wrong search method, the repair would probably lead to partitions that can't be accessed, or partitions may even be damaged by the actual repair. For this reason you should always enable the Undo feature, and make sure you use the correct scanning method.