Apple has today announced a new iMac update which sees the latest fourth-generation Intel quad-core Haswell processors, new graphics, next-generation Wi-Fi, and faster PCIe flash storage options added to the popular all-in-one desktop.

Hoping to get your hands on a new 27-inch iMac model, with its delightfully thin flat panel display and Fusion Drive goodness? Well, if you order now, you’ll have to wait up to four weeks for it to ship, as seen at the Apple Store website.

It appears that Apple hasn’t been able to manage to overcome its supply constraints, which we reported back in November, to make enough of these glorious machines to meet demand.

When Apple’s all-new iMacs made their debut in late November, a super speedy Fusion Drive was only available as a build-to-order option with the 27-inch models. But that’s no longer the case. Over the weekend, Apple made the 1TB Fusion Drive an upgrade option for the entry-level 21.5-inch iMac, too.

Apple promised us its new 21.5-inch iMac would go on sale in November, and it has just about met that deadline. You can now order the Cupertino company’s sexy new all-in-one via its online store, with shipping in 1-3 business days. The 27-inch model is also available to order, but that one will take 2-3 weeks to ship.

There were a couple of big surprises yesterday at Apple’s iPad mini event. The first was the pricing of the iPad mini itself: while everyone anticipated a $249 or $299 starting price, the iPad mini actually starts at $329… a good $70 higher than devices like the Google Nexus 7.

But there was another surprise. No one heard a peep in the last few months about Apple’s new Fusion Drive, a combination solid state and platter based hard drive that “fuses” the best aspects of flash and traditional hard drive storage.

Those aspects? Solid state drives (or SSDs) over much faster reading and write speed, as well as “instant-on” boot up from sleep or power down. This leads to huge performance boosts all across the Mac. Traditional hard drives, however, have a couple key advantages: they are both cheaper and have more capacity, allowing you to easily store massive media libraries.

So what’s the point of the Fusion Drive? Simple. It’s the best of both worlds: the speed and instant-on of an SSD, with all of the storage space of an HDD. But how does it work?