On Wednesday, Apple introduced updates to the iMac line of computers, bringing the Retina display to the smallest iMac, the 21.5-inch model, for the first time. Now every iMac has a Retina display of some sort, though there are still important differences between the variously sized iMacs.

The latest, and last, iMac to join the Retina club, the 21.5-inch iMac now boasts a display with a 4K (4096 x 2304p) resolution. Apple boasts the new screens represent 4.5 times higher resolution than the previous generation.

In addition to the higher resolution screen, the new smallest iMacs have an optional (and more expensive) build that brings a quad-core Intel Core i5 Broadwell chip running at 3.1GHz, with 8GB of RAM and a 1TB HHD.

The updated Retina 4K iMac stays at the same price as the previous 21.5-inch line, which came with a 1080p screen. The base model 2015 21.5-inch iMac costs $1,500, while the older 1080p models are dropping to a base price of $1,100.

Apple also announced updates to the larger 27-inch iMac models, boosting the base screen resolution and internal hardware options for the company's upper-end all-in-one workstations.

All 27-inch models now come with a Retina 5K (5120 x 2288p) screen, standardizing all variants of the largest iMac with the same resolution. Those iMacs feature the newer Skylake quad-core 3.3GHz Intel Core i5 chipsets with 8GB of RAM and an AMD Radeon R9 M395 GPU with 2GB of dedicated memory. The two updated lower-end 27-inch iMacs remain at the same prices, $1,800 and $2,000, respectively, while the top-of-the-line iMac has dropped in price by $200 to $2,300.

Apple updated both 4K and 5K Retina screens with a wider color range (P3) than the old sRGB standard, offering a 25 percent increase in the depth of its color space which the company is promising will lead to richer, more lifelike detail.

Speaking of across-the-board changes, all iMacs of every size now come with two Thunderbolt 2 ports for high-bandwidth peripherals. And the company updated some of its available accessories with sleeker designs: the Magic Keyboard, Magic Mouse 2 and Magic Trackpad 2.

Of particular note, Apple's Magic Trackpad 2 now comes with Force Touch, offering the same variable click depth that it first introduced in the new MacBook line, but now on any iMac or Mac Pro.

One downside of Apple's revised iMac line is that its stock Fusion drive -- the hybrid solid-state (SSD) and hard drive (HDD) storage option -- has been downgraded to 24GB SSD, from the standard 128 SSD base from last year. And it's strange that the new iMacs come with two Thunderbolt 2 ports while not updating any USB ports to the upcoming (and faster) Type-C standard.

But overall, the all-Retina iMac update is a positive move, especially because Apple managed to keep the price point consistent, and even lower it in one case. The Cupertino giant has made all of the new iMacs available on Apple's website as of the Wednesday announcement, with shipping beginning on Friday.