Windows 7 is an operating system that was produced by Microsoft as part of the Windows NT family of operating systems. released to manufacturing on July 22, 2009,  generally available on October 22, 2009.

Step 1: Visit Microsoft's Download Windows 7 Disc Images (ISO Files) page.
Step 2: Enter your valid Windows 7 product key and verify it with Microsoft.

Step 3: Choose your language.

Step 4: Click the 32-bit or 64-bit option.

Step 5: Download the Windows 7 ISO image to your computer.

Step 6:  You should now have a fully working legal Windows 7 ISO file.

Feature
Windows 7's new features 1) Touch and handwriting recognition, 
2) support for virtual hard disks, improved performance on multi-core processors improved boot performance, Direct Access, and kernel improvements. 
3) Windows 7 adds support for systems using multiple heterogeneous graphics cards from different vendors a new version of Windows Media Center, a Gadget for Windows Media Center, improved media features, XPS Essentials Pack and Windows Power Shell being included, and a redesigned Calculator with multi-line capabilities including Programmer and Statistics modes along with the unit conversion for length, weight, temperature, and several others.
4) Many new items have been added to the Control Panel, including Clear Type Text Tuner Display Color Calibration Wizard, Gadgets, Recovery, Troubleshooting, Workspaces Center, Location and Other Sensors, Credential Manager, Biometric Devices, System Icons, and Display. Windows Security Center has been renamed to Windows Action Center (Windows Health and Windows Solution Center), which encompasses both security and maintenance of the computer. Ready Boost on 32-bit editions now supports up to 256 gigabytes of extra allocation. Windows 7 also supports images in RAW image format through the addition of Windows Imaging Component-enabled image decoders, which enables raw image thumbnails, previewing and metadata display in Windows Explorer, plus full-size viewing and slideshows in Windows Photo Viewer and Windows Media Center. Windows 7 also has a native TFTP client with the ability to transfer files to or from a TFTP server.

Windows 7 system requirements
•           1 gigahertz (GHz) or faster 32-bit (x86) or 64-bit (x64) processor*
•           1 gigabyte (GB) RAM (32-bit) or 2 GB RAM (64-bit)
•           16 GB available hard disk space (32-bit) or 20 GB (64-bit)
•           DirectX 9 graphics device with WDDM 1.0 or higher driver.