iMac 24in 2.8GHz review

Apple's latest iMac line-up may have slipped onto the market almost unnoticed and reaction to it been somewhat muted, but, as we hinted at last issue in our New iMacs feature, there have been some pretty significant changes behind the all-in-one Mac's glossy screen.

As such, we were keen to see how those modifications translated into test results and improvements in real-world use.

Having now had a chance to test the 24in 2.8GHz model, we're impressed. Very impressed. The improvement in raw processor performance is significantly greater than a megahertz bump from 2.4GHz to 2.8GHz would suggest. In fact, the 2.8GHz iMac showed an increase of more than 50% in raw processing power.

This boost can probably be attributed to a combination of two things: the switch from Merom to Penryn Core 2 Duo processors and an increase in frontside bus speed - the channel through which data is shuttled between processor and Ram - from 800MHz to 1066MHz. The switch to Penryn brought a 50% increase in cache, from 4MB to 6MB, and an improvement in clock speed management. The clock speed improvement, known as EDAT, is particularly beneficial to applications that aren't written to take advantage of multiple cores.

Penryn also uses power more efficiently than Merom, cutting down on the overall power needed by the iMac and reducing the heat it generates and, as such, the cooling it needs. This in turn reduces the need for fan cooling and therefore allows the iMac to run more quietly.

There's more to these new iMacs than a change in processor architecture, though. The base Ram configuration has been bumped up to 2GB, although as Ram is relatively cheap, you might as well fit the maximum 4GB. The graphics chip is still ATI's Radeon HD 2600 Pro with 256MB of Ram in this model. There's now an option to upgrade it to an Nvidia GeForce 8800GS with 512MB of Ram. At £90, this is a worthwhile upgrade if you plan to use the iMac to play games or run 3D modelling and rendering applications, but it's still a pretty modest performer by PC standards.

The 320GB 7200rpm hard drive is a decent performer and can be upgraded to a 500GB, 750GB or 1TB drive for £30, £90, and £180 respectively. The alternative to upgrading the internal hard drive is to add an external drive at a later date using one of the iMac's five USB 2 ports (two of which are on the keyboard and two of which are used for the keyboard and mouse), FireWire 400 port or FireWire 800 socket. Alongside those ports on the back of the iMac are a Gigabit Ethernet connector and a mini-DVI output. The latter can be used to mirror your iMac's desktop or, if 1920 x 1200 pixels isn't enough room for you, to span it across two displays.

The iMac's glossy screen was something of a bone of contention when it first appeared last summer, but having used one daily for the past few months, we're very comfortable with it. It does reflect more light than a matt screen, but unless you sit in front of a window, this isn't a big issue. It's worth noting that the 24in iMac's screen is an 8bit panel that displays 24bit colour or 'true' millions of colours, as opposed to the 20in iMac, which has a twisted nematic (TN) 6bit panel that uses dithering to display millions of colours. There were reports of early aluminium 20in iMacs last summer having 'washed out' displays, and this was attributed by some as being the result of using a TN display. However, while it's true that if you place a 24in and 20in iMac next to each other, there's a detectable difference, the image on a 20in iMac is far from washed out and is absolutely fine for everyday use.