iMacs are a bit like the Cambrian period in geology, about 540 million years ago. At first there was a great outpouring of new, and, frankly, utterly weird life forms: "Hopeful Monsters", they were dubbed. Strange but optimistic species that turbo-charged evolution for a few million years, with the successful ones having a huge influence on future life even today. But most of them didn't survive: brave attempts at living but ultimately too strange; too ill-adapted for the mainstream.
Remember the first iMac in 1998? It was turquoise and transparent. And it didn't have a floppy disk. Pretty shocking at the time. But just about every gadget from the Far East cheerfully copied the design ethos: see-through consumer products became the norm. And then, five years later, there was what I think was the strangest of all: the love child between a desk lamp and a laptop. A clever design that vanished as quickly as it arrived.
But what came next has stuck around for a decade and a half: first in the form of a white poly-carbonate "screen" containing the actual computer, and then the familiar aluminium (aluminum) iMac.
The current version of this contains a powerful computer housed in an impossibly thin-looking case. Unless you're an out-and-out power user, this is the tabletop Mac you're likely to buy if you're a creative (although the new Mac Mini is looking like a contender in this market if you already have screens, keyboards, etc).
Specifically, the 21.5 inch iMac moves to an 8th-generation quad-core. These are 6-core processors, with a claimed 60% faster performance.
The 27-inch iMac now has a 9th-generation 6-core or 8-core processor with a claimed 2.4 times speed boost.
Graphics have been improved as well, with the arrival of AMD Radeon Pro graphics. The 21.5 inch iMac receives a claimed 80% graphics boost, and the 27 inch is 50% faster.
I can't help feeling that the 27 inch iMac is a really good machine: a great screen, pretty powerful for everything except "power computing", and it looks great (which matters to professionals).