What type of optical-disc add-on did Microsoft release for the Xbox 360 in 2006?

Microsoft released an HD DVD drive add-on for the Xbox 360 in 2006.

The Xbox 360 HD DVD Player was an external accessory that connected to the console through USB and played high-definition HD DVD movie discs. Microsoft launched it in November 2006, during the format competition between HD DVD and Sony's Blu-ray Disc.

The accessory did not replace the Xbox 360's built-in DVD drive. It was an optional peripheral intended for customers who wanted high-definition film playback, and it could not play Xbox 360 games because those games used standard DVDs.

Blu-ray ultimately won the format contest after major studio and hardware support shifted toward it. Toshiba discontinued HD DVD in 2008, and Microsoft stopped producing the Xbox 360 add-on. This makes the accessory a notable but short-lived part of Xbox hardware history.