Microsoft has revealed some of the hardware requirements to run the desktop version of Windows 10 when it is released this summer. The below slide does not go over everything, but does discuss memory, storage, graphics, screen size and firmware requirements.
So for Windows 10 you will need an 800 x 600 or higher display, 2GB of memory for the 64-bit version, 1GB of memory for the 32-bit version, 20GB of storage for the 64-bit OS, 16GB of storage for the 32-bit OS and a DirectX 9 or higher graphics card. Other things that are required is a UEFI BIOS 2.3.1 and secure boot enabled.
Source: TweakTown | News Archive