Unpartitioned Portion of My Hard Drive? (1 Viewer)

[Kevin_Graham]

When I started to re-install XP last night it showed that my C: drive is partitioned with NTFS format. It also showed that I have 8mb of an unpartitioned area on my drive. Huh?? Is this an area XP sets aside for processing?

 

[Ted Lee]

my hd (also running xp) is in a similar situation.

i don't think any hard drive is ever *completely* formatted? i can't remember why though.

also, i believe you can use certain utilities (like partition magic) to reclaim that space?

 

[Rob Gillespie]

I think it just comes down to the math involved with the number of cylinders. Anyway, 8mb is nothing, really.

 

[Wayne Bundrick]

I think it has something to do with the minimum size increment that can be made in the partition table. The next size up would be slightly bigger than the disk, so it can't be used. But like Rob said, it's just 8 megabytes, and if your drive is today's typical size then it's nothing compared to 40,000 or 60,000 megabytes. Don't worry about it.

 

[Ken Chan]

I'm guessing it's this: the master boot record (MBR), which contains the partition table, is always in its own cylinder, number 0. The first (or only) partition starts on cylinder 1.

All modern drives are defined to have 63 sectors per track, and 255 tracks per cylinder, or sides. (This is a fiction of address translation; your drive does not have 128 platters.) 63 * 255 * 512 bytes/sector is about 8 MB.

//Ken

 

[John_Berger]

I'm guessing it's this: the master boot record (MBR), which contains the partition table, is always in its own cylinder, number 0. The first (or only) partition starts on cylinder 1.

That might very well be true; however, this required 8 MB partition does not occur in DOS/Win 3.1/Win 9x which obviously also requires an MBR. It started with Windows 2000, upon which Win XP is based.
I'm not saying you're wrong - plese don't misunderstand. Your analogy is quite sound; however, my guess would be more of the NT/2000/XP Disk Management function, or a combination of MBR and Disk Management. For example, if you attempt to run Disk Management for the first time on a fresh hard drive, it will look someplace on the hard drive and say that the disk has not been initialized, or something to that effect, so that Disk Management can maintain it. "Do you wish to make changes to the disk?" (or something similar) will then appear stating that it will write changes to the disk. That might also be what that hidden partition is for.
I noticed that both 2000 and XP reserved that 8 MB area on my 3 GB, 30 GB, and 100 GB hard drives, even though only two are boot drives and one is a permanent D: drive. (Removable hard drives, in case you're scratching your head right now.) This never appeared with the DOS/9x fdisk where you are even prompted with "Do you want to use all available space for the primary partition?"
Just my two cents. I've been wondering what the 8MB is all about as well.

 

[John_Berger]

Found it!
http://support.microsoft.com/default...b;en-us;225822

SYMPTOMS
During Setup, if you choose to create a partition that uses the remaining space on a disk, you cannot use the maximum space available on the disk.
For example, if you choose to create a 4096-MB partition on a disk that has only 4096 MB available, the actual partition that is created may be 4095 MB or less in size.
CAUSE
Some space at the end of the disk is reserved by Setup in case you later want to upgrade the disk to a dynamic disk. Dynamic disk information is saved at the end of the disk. The amount that is reserved is a minimum of one cylinder, or 1MB, whichever is greater. One cylinder can be up to 8MB, depending on drive geometry and translation.

The knowledge base article specifically refers to Windows 2000; however, XP is Windows 2000 at its core, so I have no doubts that that is why it also occurs in XP.

 

[Kevin_Graham]

John - Great find!

 

[Ted Lee]

who da man? john da man!

err...wait...yo-da....err...never mind. :b

 

[John_Berger]

 

[Ken Chan]

this required 8 MB partition does not occur in DOS/Win 3.1/Win 9x

It's not a partition; and I recall seeing the same cylinder used by the MBR for disks formatted by DOS. Of course, the disks were a lot smaller and the geometry wasn't as wacky, so the "wasted" space is not 8 MB.

So basically it's a reserved cylinder, either at the beginning or the end. A quick check of the partition table would settle it, if anyone was interested enough....

//Ken

 

[Ken Chan]

On second thought, they might have reserved just the first track. In that case, never mind
//Ken