Apple has announced new desktop computers, adding a 21.5-inch iMac model with Retina display to the lineup, as well as some new accessories for other models.

The 21.5-inch iMac is getting a major screen upgrade to a 4K display with a resolution of 4,096 x 2,304 pixels. The older 21.5-inch iMacs only had 1080p displays. Apple says that, in addition to the resolution improvement, users will notice 25 percent more colors because of a new display technology behind the screen panel, Tech Radar reports.

The updated 21.5-inch iMac is also receiving some slight upgrades to its internal components. An Intel Broadwell processor will be included in the 4K version, which will run at 3.1GHz. The newest chip for computers today is the Skylake processor from Intel, but Broadwell chips are still fairly new. By using the Broadwell chips, Apple was able to include Intel Iris Pro graphics.

The new model also gets a boost in RAM from 8GB of 1600MHz LPDDR3 to 8GB of 1867GHz LPDDR3. Users can upgrade to 16GB of RAM if they choose.

The 4K 21.5-inch iMac will start at $1,499 and is shipping now.

Another exciting development for the iMac is the new trackpad and keyboard. These standalone accessories will now be powered by internal batteries instead of AA batteries. The new batteries can be charged through a Thunderbolt cable and will last up to a month on a full charge, The Verge reports.

The trackpad has also improved a lot over the last version. A downsloping trackpad allows users to click anywhere and offers a wider surface. It also supports Force Touch. However, the new trackpad costs $129, nearly twice the price of the older version.

The keyboard has improved as well, with wider keys and a subtle slope, making typing more enjoyable and accurate. The trackpad and keyboard will fit perfectly side by side. The new keyboard costs $99, a $30 increase from the older version.

Finally, the premium 27-inch iMac will get 5K screens on all of its models. This ultra-sharp screen will feature the same new color technology powering the 4K 21.5-inch iMac.

The 27-inch 5K iMac will start at $1,799 for the most basic model and rise in price from there. It will start shipping from Apple's website Tuesday and be available at select retailers soon.