You can keep a keep a copy of Windows 7 installer in your USB pen drives . This is very useful as they are handy and can be carried anywhere . the USB pendrive should be made bootable ,in order to install Windows 7 using them . Installing Windows 7 from USB pen drive is pretty faster compared with DVD/ CD installation .
For this you need a USB 2.0 drive with 4GB or more capacity . Then a ISO file for Windows 7 installation .
Follow these instructions :
Step1 : Format your USB 2.0 in NTSF format .
Step2 . You have to create a Virtual drive in your hard disk . For this you can use program like slysoft virtual cone DVD .Virtual Drive works and behaves just like a physical CD/DVD drive, however it exists only virtually .That is , mount your Windows 7 ISO image to the virtually created drive .
Step 3 : From start menu , as shown as in the screen shot , right click on command prompt and select to run as administrator.
Step4: The above step opens Windows 7 command prompt . You have to enter a series of commands exactly as shown below .
Type " diskpart " ( without quotes)as hit enter (This will open Windows disk partition utility )
Type "list volume" to display the available drives . ( click on the image to make it larger )
Select your pendrive from the list - Type and enter "select volume 3" ( 3 stands for your USB drive name)
Step 4 : Enter "active " and then "exit "
Step 5 : Now enter the name of your virtual drive" M:" ( assuming it as M)
Step 6 : Again enter "cdboot "
Step 7: Here comes that last command - Enter " bootsect/nt60 3: " ( Your USB pendrive name is assumed as 3)
Step 8: Copy all content from your Virtual drive M to USB drive . Now you have created a bootable Windows 7 USB drive .
Restart your PC > Press Del and enter in BIOS mode .
Open up boot priority and it change from hard disk/ DVD to USB .
Now you will be able to install Windows 7 from USB pen drive .