Mirroring is a technology known as RAID1 (Redundant array of Inexpensive Disks). This technology allows to have a fault tolerant disk in the event of a hardware failure of you main hard drive. The idea goes like this. You have two hard drives of relative equal size and preferably same make and model. Then you mirror the first disk to the second disk. Everything that is written to the first disk is written to the second disk. Should the first disk experience a hardware failure or fault. The second disk continues to operate, so you can continue to work without interruption. At you earliest convenience you can replace the failed disk, and restore the mirror. Lets see how this is done
First add a disk of the same size as the one you have in your computer. Typically this will be a new sata disk. Connect the sata disk two one of the remaining sata port on the motherboard. Turn on the computer and go to the computer management console. Then select disk management.
The Initialize disk dialog box will show a new drive has been added to Windows. Click ok to initialize disk
You now have two disks. One with Windows, and one unallocated.
Right mouse click the disk that currently has Windows, this will usually be the C: drive. Then select from the context menu, Add mirror
Select the disk, and click add mirror button. Click Yes on the warning
Windows starts synching the disks.