Microsoft made a lot of big announcements at its press conference at the E3 2015 event, but one of the biggest is that gamers can now play old Xbox 360 games on Xbox One.

Backward compatibility for Xbox 360 games on Xbox One consoles is a big deal indicative of the huge applause the announcement received from the crowd at the conference.

With this new backward compatibility feature, owners of Xbox One consoles will be able to play select titles of their previously purchased Xbox 360 games.

Starting today Xbox One preview members can play a selection of Xbox 360 titles they already bought with Microsoft aiming for about 100 title before the holiday.

Titles like A Kingdom for Keflings, A World of Keflings, Mass Effect, Perfect Dark, and Perfect Dark Zero are now backward compatible. In all about 21 titles are compatible. See full list

All a developer needs to do for an Xbox 360 title to become backward compatible with Xbox One is to approve it. So, you should expect the lineup of Xbox One compatible games to increase.

Gamers will be able to play their compatible Xbox 360 games on Xbox One no-matter the distribution method, whether disc, digital, or inter-console multi-player.

This means that Xbox One gamers will soon be able to play multiplayer Xbox 360 titles with their friends on the older gaming console.

The presentation was not just about Xbox One compatibility, Microsoft also unveiled about four indie titles (Tacoma, Ashen, Beyond Eyes, and Cuphead) that will be coming first to the Xbox One before other consoles.

Another big announcement was that mods created for the PC version of the Fallout 4 will be supported on the Xbox One, which means that Microsoft is about the leverage to popularity of the PC on its gaming console.

But, no doubt the ability to play Xbox 360 games on Xbox One will resonate with the Xbox crowd. It could also help the Xbox 360 catchup its major competitor the Sony PS4.