Windows 7 is available in six flavors : Starter, Home Basic, Home Premium, Professional, Enterprise and Ultimate Editions. Minimum System Requirements.
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Windows 7 Minimum System Requirements

Windows 7 with Aero desktop features needs to fulfill following minimum requirements:

Feature 32 Bit 64 Bit
Processor

1 Gigahertz or Faster
32-bit (x86)

 1 Gigahertz or Faster (x64)
RAM 1 GB 2 GB
Hard Disk Space 16 GB of available hard disk drive space 20 GB of available hard disk drive space
Graphics Support for DirectX 9 graphics with Windows Display Driver Model (WDDM) 1.0 or higher driver and 128 megabytes (MB) memory (Aero theme) Support for DirectX 9 graphics with Windows Display Driver Model (WDDM) 1.0 or higher driver and 128 megabytes (MB) memory (Aero theme)
Optical Drive Internal or external DVD drive Internal or external DVD drive
Monitor Minimum 1024 x 768 resolution Minimum 1024 x 768 resolution