Apple's online store went down for a short period today, and now we know why - it's updated its iMac line.

Apple has introduced a low-power 21.5-inch iMac for the price of £899 ($1,099, AU$1349), reducing the cost of its most affordable model by £150 ($200).

The iMac comes with a 1.4GHz dual-core Intel Core i5 processor, 8GB of RAM, Intel HD Graphics 5000 and a 500GB hard drive. Of course, those specs can be upgraded if you so wish.

And you can still go and buy the previously-cheapest iMac, which clock in at a slightly more powerful 2.7GHz with the same screen size.

So why has Apple done this? Plenty of reasons, but to pave way for Retina models later this year would be our bet.