Today's iMac comes in four primary configurations, with a fifth designed specifically for the education market. Let's look first at what they all have in common, then explore the differences, remembering that like most computers, these are all upgradable.
All new iMacs sport Intel's Thunderbolt I/O technology, which at a bi-directional 10Gbps (gigabits per second), makes USB2 -- the current standard at 480Mbps (megabits per second) -- seem like the Pony Express [source: Kingsley-Hughes]. Thunderbolt is also twice as fast as the likely dead-on-arrival USB3, which promises a maximum speed of 5Gbps. Unlike the first iMac, which omitted the floppy drive and left users no way to access their existing storage, these new iMacs still include USB ports for all your legacy (but likely soon-to-be-obsolete) devices.
Adding to this speed are the quad-core Intel Core i5 processors at speeds ranging from 2.5GHz to 3.1GHz. All but the most inexpensive iMac come with a 1TB (terabyte) Seagate hard drive. It's worth noting that iMacs sold in May and June 2011 had some serious issues with the 1TB hard drive, so Apple is replacing them for free at Apple Stores or through a mail-in service [source: Apple]. Other common features include built-in 802.11n wireless and Bluetooth networking.
The educational iMac is a bit pared down. Available only to schools, it uses a slightly-older Core i3 processor and no Thunderbolt I/O, but otherwise is a decent value at $899.
The main iMacs come in at four price points: $1199, $1499, $1699 and $1999. The first two come with a 21.5-inch screen and the second group with a 27-inch screen, both offering 16:9 aspect ratio (some earlier iMacs curiously used a non-standard 16:10 ratio).
The $1199 model comes with a 500GB hard drive, unlike the three pricier models with the 1TB drive we mentioned earlier. The two most expensive models also include two Thunderbolt ports compared to one for the other models. If you're big into heavy-duty graphics or plan on that second display, consider getting one of these models.
Overall, the specs and speed are comparable to current desktop PCs, though PCs have yet to use Intel's Thunderbolt I/O. Apple's exclusive use of this technology (thanks to Apple's collaborative effort with Intel to develop it) ends in 2012, at which time it'll be open season for other manufacturers.
All this power's no good unless it's doing something. Time to find some cool software to play with (and a lot of it's free).