While computers that have been running on Windows 7 would have no problems in migrating over to Windows 8, the same is not going to be the case for tablet devices. Microsoft has announced some limited specification as mandatory for the tablet devices to be able to run on Windows 8.
For a start the tablet must have a minimum of 10 GB free capacity after the new OS has been loaded. It also needs to have UEFI firmware on the device along with WLAN. The device must be Bluetooth 4.0+ LE enabled and have Direct 3D 10 with WDDM 12 driver. Screen should have 5 point multi-touch capability and a minimum resolution of 1366 x 768 pixels. Other mandatory requirements are a 720p capable camera, a magnetometer, accelerometer and gyroscope. It should also be able to sense light of 1-30 lux range, while the dynamic range should be in the 5-60k bracket. Microsoft have also mentioned that the tablets must have the power, rotation lock, Windows key and volume up/down buttons on the tablet and must support NFC. It should also have a USB 2.0 port.
This, as per Microsoft, will ensure that all tablets with Windows 8 as the OS will function uniformly. Lastly, Windows 8 will also include the famous CTRL + ALT + DEL replacement for tablet like device that do not include a physical keyboard — Windows Key + Power which will pull one out of uncomfortable and awkward situations during computing.