Google Nexus 4 is powered by a 1.5 GHz quad-core Qualcomm Snapdragon S4 Pro processor, featuring four Krait cores and the class-leading Adreno 320 GPU. In addition to the fast processor, the Nexus 4 also packs 2 GB of RAM and either 8 or 16 GB of internal storage. The device also features a 4.7″ 720p display, delivering 320 ppi.
Nexus 5, Nexus 6, Nexus 7 2012 and Nexus 10 have received the Android 5.1 factory image while the Nexus 4 is yet to receive one. But the Nexus 4 can still be updated to Android 5.1 via the unofficial AOSP ROM. If you want to install Android 5.1 on Nexus 4, follow this guide.