• Physically, the Galaxy S4 didn’t get any bigger. In fact, it even sports a thinner build and weighs a hair lighter. But with a slimmer bezel, it has 5-inch full HD Super AMOLED display at 441ppi compared to the 4.8inch 1280 x 720 display of S3 at 306ppi.
• In terms of processor is the major update to a 1.6GHz octa-core Exynos 5 Octa from the proprietary 1.4GHz quad-core Exynos processor in S3 . The benchmarks are yet to be released so wait for performance increase.
• In the international version S4 sports a 2GB RAM compared to 1GB in S3
• Galaxy S4 also recieved a bump in the camera from 8-megapixel of S3 to a 13 megapixel in Galaxy S4.
• The Galaxy S4 has a newer Android 4.2.2 Jelly Bean compared to Android 4.1 Jellybean of S3 but again S3 will also receive the 4.2 update in coming months. S4 got many new smart features like Smart Scroll , Smart Pause , Dual Camera Shoot , Air Gesture etc
• Finally the battery is beefed up to 2,600mAh from 2,100mAh.This was necessary as to sport a a larger FULL HD display and Exynos Octa Processor comparison