You may ask “why? why do i have to boot Windows OS from an external HDD on my Desktop machine?”. First answer could be “from security reasons”, but the list might continue with “I have the same machine both at home and at the office”, “I have both extremely confidential information on it and this require more processing power than a laptop can provide”, etc.
Remember that 2.5 is laptop HDD size, it can be stored/carried easily and your Desktop PC will become HDD-less.
What you need: 2.5 eSATA external HDD enclosure (rack), 2.5 SATA HDD (at least the same size as the HDD to be cloned), HDD cloning software.
1. Insert the 2.5 SATA HDD in the 2.5 eSATA Rack (I used Zalman ZM-VE200 SE), connect it to your PC using the eSATA cable (patch cord) and powering it through USB cable.
2. Use a HDD cloning software (such as Norton Ghost or Acronis True Image) and clone the internal 3.5 HDD including MBR data on the brand new 2.5 HDD.
3. After the cloning process has successfully finished, turn off the PC, remove the 3.5 HDD, and start the computer. Make sure that you have the “booting from external storage” enabled in BIOS.
That should be all. Have fun!