The iPhone 4 was the first iPhone to mark a step change in Apple’s design language. Other manufacturers would later adopt the new flat design, as well as the stainless steel frame that doubled as an antenna. Yet the biggest visible change was in the screen, as Steve Jobs introduced the Retina Display.

This is Day 9 of 30 Days of iPhone, a look at the moments that shaped the smartphone era .

How Many More Pixels Were On The iPhone 4 Display?

With a resolution of 960 by 640 pixels, the 3.5-inch LCD panel had a pixel density of 325 pixels per inch. Jobs cut through the numbers with a simple line; the human eye couldn’t distinguish pixels when viewed normally. This made web pages, images, and pages of text feel closer to the sharpness of print than the blocky look of the competition, which was forced to catch up to match iPhone specifications.

Apple’s Retina Display branding made its way to displays on products from the iPad and MacBook through to future products such as the Apple Watch. While resolution and ppi changed by device, the “indistinguishable when used normally” claim was universal. It would take more than a year for Android manufacturers to offer similar displays (such as the Galaxy Nexus’ 316 ppi launched in October 2011).

The Impact Of The iPhone 4’s Retina Display

With the introduction of the Retina Display, Apple lifted expectations on what a smartphone screen should offer. You can draw a direct line to the proliferation of 2K resolution displays readily available today, from basic mid-range handsets right up to the flagships.

This is Day 9 of 30 Days of iPhone. Yesterday we looked at the iPhone 4 prototype that was left at a bar and leaked to the world .