Vista's New Partitioning Rules
The old partitioning conventions have been dropped.
For nearly 30 years there has been a standard to the way basic partitions have been organised and positioned on the common IDE/SATA hard drive. In coming years the continuing expansion of drive sizes is going to mean a change to hard drive geometry that will force the old standards of partitioning to be updated. Microsoft have agreed to help facilitate this change by making Vista ready for the new drives. Partitions created by Vista are using new rules that are not entirely compatible with all previous versions of Windows or most current third-party tools for partitioning, imaging and cloning. Some third-party vendors are trying to catch up and are releasing “Vista Compatible” versions, but at least two that I know of have been premature in this claim.
Put simply, Vista is placing partitions on the hard drive using different starting and ending positions from the recognised conventions. This means that when most other partition altering applications are used they are likely to re-align the partition during operations to the default norms, which can change both the starting and ending sectors of that partition. This causes a problem because Vista uses the starting sector value (the offset) in its boot process, so a re-aligned Vista OS will not boot. (See Vista's Boot Files).Update: March 2010 In the 3 ½ years since Vista went RTM most, but not all, actively maintained partitioners, imagers and cloners seem to have caught up, either by working to the new rules, or by auto editing a necessary boot file (the BCD) to account for a moved partition offset. I can’t test all such apps and of those that I have it has been in too limited a fashion for me to be comfortable recommending any.
Finding exact information on Vista's new partitioning rules has proved elusive and so far I’ve only seen this one KB article explaining the reason for the offset change to the first partition on the hard drive, but with no mention of the ending sector or the following partitions. One other very brief KB page gives notice to a serious incompatibility issue between Vista and XP that could delete your Vista partition. Also see The case of the disappearing partitions. Two more KB pages describe why you might not be able to install XP or 2003 to a Vista created partition, they then offer a registry workaround to make Vista stop using the new rules.
If you only have Vista on your computer and don’t mess with imaging or cloning then you have nothing to worry about. However if you do image or clone your drive or have a dual or multiboot configuration with OSes other than Vista, then there are various serious problems that can arise. For now the best solution is to not let Vista create partitions, but do it with previous Windows OSes or with third-party tools. When installing Vista you should create the partition yourself beforehand and point the Vista install to that partition. Vista is perfectly happy to follow the standard conventions and I have not seen any issues when everything has been done by the old rules using XP compatible tools. Many current apps that worked with XP can be used with Vista, however many might not install inside Vista but they can be used from inside another OS or boot disk. When there have not been any Vista created partitions on the drives I have successfully used several non-Vista versions of partitioning, imaging and cloning tools. I obviously can’t test all the functions of all such apps in all possible OS, drive and hardware combinations, so test your own apps on your own setup before relying on them. There are of course issues with the BCD store and the Disk Signature when imaging and cloning, but these are not always related to partition structure and are dealt with on other pages of this site.
When you add the problems of maintaining the unusual drive letter assignments caused by the Microsoft bootmanager into the mix with the BCD, Disk Signature and the new partitioning scheme, then it’s hardly surprising that third-party vendors are struggling to catch up. The possible variations of OSes and partition types on multiple hard drives is going to be a minefield. I would suggest remaining wary of "Vista Compatible" imaging apps for the time being.
If you have already decided to follow the advice of not letting Vista create your partitions then you do not have to read any further. If you don’t know what cylinder boundaries or sectors and tracks are, then you will need to brush up on the basics. http://www.pcguide.com/ref/hdd/geom/tracks.htm
On the new drives the individual sectors are going to be larger in size. At present they are 512bytes each, the new sector size will most likely be 4096bytes, which is 8 times larger. There may be a slight drop in overhead from not having to address 8 separate sectors, but the real advantage comes from less error control and the resulting saved disk real estate. On present hard drives the ECC (Error Correction Code) can account for up to 10% of disk space and projections have put this as high as 40% if sector sizes remained at 512bytes. So we need larger sectors and it makes sense to update partitioning conventions to best suit the new hard drive geometry and modern operating systems and software. If you want to read more then there are links at the bottom of this page.
Current partitioning rules will always start the first primary partition on the 64th sector, leaving the first 63 sectors (31.5kb) for the MBR. This aligns the partition with the old CHS track boundary and so starts the partition on what would have been the first sector of the second track. Vista by default leaves a 1MB offset at the start of a drive, which results in 2048 sectors not used by the partition, (on the new drives 1MB will be 256 sectors). I've also found the ending sector of any Vista created partition will not be aligned to a cyl boundary, but will be short of it by a couple to several thousand sectors. I’m not sure what criteria Vista is using to decide the ending sector, but it looks like it may simply be the multiple of 2048 that is closest to the requested size. With partition sizes of round gig numbers like 10gig, 20gig etc, the ending sector number will usually finish with the digits 2047 – e.g. xxxxx2047 (counting sectors from zero). Any partition created by Vista will follow the new rules, so if you create another partition after a Vista one it will start on the very next sector of xxxxx2048, and likely end on xxxxx2047. With non-round partition sizes the start and end numbers still often maintain the last two digits – xxxxxxx47, to - xxxxxxx48. An extended partition at the end of the hard drive also starts with the new Vista rules, but appears to finish at the end of the drive. Logical partitions are also subject to the new rules, with each one having the 2048 offset from its partition table to the PBR. (Sector numbers I've shown are only if all partitions on the drive have been made with Vista).
Microsoft themselves have already been caught out by the new partitions, as the “Disappearing Partitions” issue linked to above has shown. Perhaps XP views the hidden sector value of the Vista logical as invalid, or maybe it’s just the fact that the partition is not on cyl boundaries. If XP finds a logical it is happy with before the Vista one/s then it writes the details of the partition it has been asked to create into that one's partition table, which overwrites the record of the logical/s in-between. I have also since seen a couple of other situations where logical partitions can get deleted, both by XP and Vista.
References and reading:
4K Byte-Sector HDD-Data Format Standard (.doc download)
ATA/ATAPI-7 Support for 4K Sector Drives (.doc download)
The two above documents (HGST WinHEC 2005 White Paper - HGST ATA Standard
Proposal) can be had direct from:
Configuring Disk Alignment
How Windows NT Handles Drive Translation
The following links are also in the text above:
Windows Vista support for large-sector hard disk drives
The partition that hosts Windows Vista may disappear if you use Windows XP to create
You cannot install Windows XP successfully after you use Windows Vista
You cannot install Windows Server 2003 successfully after you use Windows
The Case of the Disappearing Partitions