What ARM-focused edition launched alongside Windows 8?

Windows RT was the ARM-focused edition launched alongside Windows 8. Microsoft designed it for tablets and other devices using ARMv7 processors, emphasizing battery life, thin hardware, and system-on-chip designs.

Unlike standard Windows 8 editions for Intel-compatible processors, Windows RT could not run conventional x86 desktop applications. It supported specially compiled Windows Store apps and included a limited ARM-optimized desktop, including Office RT. Microsoft also released its own Surface tablet running Windows RT on the Windows 8 launch date.

Windows RT is often confused with Windows 8 itself or with Windows Phone. It shared much of Windows 8's interface and features, but its processor architecture and software restrictions were different. The “RT” name was not presented by Microsoft as a clearly defined abbreviation, although it was widely associated with Windows Runtime.