field tests, varies widely among different human subjects. In practice, thus far Apple has converted a device's display to Retina by doubling the number of pixels in each direction, quadrupling the total resolution. This increase creates a sharper interface at the same physical dimensions. The sole exception to this has been the iPhone 6 Plus, 6S Plus, 7 Plus, and 8 Plus, which renders its display at triple the number of pixels in each direction, before down-sampling to a 1080p resolution. Models The displays are manufactured worldwide by different suppliers. Currently, the iPad's display comes from Samsung, while the MacBook Pro and iPod Touch displays are made by LG Display and Japan Display Inc. There was a shift of display technology from twisted nematic (TN) liquid-crystal displays (LCDs) to in-plane switching (IPS) LCDs starting with the iPhone 4 models in June 2010. Apple markets the following devices as having a Retina display, Retina HD display, Liquid Retina display, Liquid Retina XDR display, Super Retina HD display, Super Retina XDR display or Retina 4K/5K/6K display: Reception Reviews of Apple devices with Retina displays have generally been positive on technical grounds, with comments describing it as a considerable improvement on earlier screens and praising Apple for driving third-party application support for high-resolution displays more effectively than on Windows. While high-dpi displays such as IBM's T220 and T221 had been sold in the past, they had seen little take-up due to their cost of around $8400. Reviewing the iPhone 4 in 2010, Joshua Topolsky commented: "to our eyes, there has never been a more detailed, clear, or viewable screen on any mobile device. Not only are the colors and blacks deep and rich, but you simply cannot see pixels on the screen…webpages that would be line after line of pixelated content when zoomed out on a 3GS are completely readable on the iPhone 4, though the text is beyond microscopic." Former Microsoft employee Bill Hill, an expert on font rendering, offered similar comments: That much resolution is stunning. To see it on a mainstream device like the iPad—rather than a $13,000 exotic monitor—is truly amazing, and something I've been waiting more than a decade to see. It will set a bar for future resolution that every other manufacturer of devices and PCs will have to jump. Writer John Gruber suggested that the arrival of Retina displays on computers would trigger a need to