Our initial review of the MacBook Air was based on its stock £1,199 configuration, which features a 1.6GHz Intel Core 2 Duo processor and 80GB of storage provided by a 1.8in traditional hard drive.

Since then, we've obtained two 1.8GHz Intel Core 2 Duo MacBook Airs: one with the same 1.8in 80GB hard drive, and one with 64GB of flash memory as its primary internal storage device (what Apple calls a solid-state drive, or SSD.)

With those three models, we can begin to assess the effects of the MacBook Air's two main build-to-order configuration options, the £190 processor-speed upgrade and the £639 SSD upgrade.

Both upgrades improve things. The processor upgrade improves calculation-based tasks such as 3D rendering and video encoding and the SSD upgrade enhanced disk-intensive tasks such as duplicating a file or launching Photoshop.

In terms of Speedmark, our battery of general-use tests, the base MacBook Air scored 124. The MacBook Air with the same hard drive but a 1.8GHz processor improved to a score of 130. The model with the 1.8GHz processor and the SSD earned 140. To put that in percentage terms, the £190 processor upgrade improved the overall speed of the system by 4.8 percent, while the £639 drive upgrade improved speed by 7.7 percent.

Of course, speed isn't the only reason to invest in the SSD option. In theory, its lack of moving parts makes it a safer storage device, because it's not exposed to the mechanical failures that hard drives with spinning platters can suffer. However, until we get a long-term read on the reliability of the SSD, that advantage remains theoretical.

Life with the SSD

We spent two weeks using a 1.8GHz MacBook Air equipped with the 64GB SSD as the primary system. It turns out that trimming down a system in order to fit on the 64GB SSD was – for us – almost impossible.

After formatting and installation of the full OS X 10.5 operating system, our fresh model showed only 35.4GB of free space. You can free up more by re-installing without certain files (printer drivers, fonts, language options etc) and by removing iLife programs that you may not use (iMovie, Garageband), but even so you really have to consider whether the 64GB drive is going to provide enough space. Especially if you are planning to use the MacBook Air as your primary Mac.

We managed to squeeze our content down to fit the 80GB option, but found the only way to get it all on to the 64GB SSD drive was to remove the 10GB Parallels Desktop Windows disk image and sacrifice the ability to run Windows.

There are two ways to measure speed: the cold, hard reality of numbers and the fluffy, fuzzy world of anecdote. Here's a splash of cold, hard reality from our Test Centre: launching Photoshop on the SSD version of the MacBook Air is stunningly fast.

We've noticed that other applications also seem to launch much faster on the SSD Air. Similarly, this Air feels more responsive when running numerous programs at once – possibly because the speedy SSD makes the swapping of programs between RAM and disk faster. The Assorted Speedmark tests table shows a few of the tasks that make up our Speedmark 5 checks. As you can see, tasks involving the hard drive are faster on the SSD model; for tests dependent on the processor, the 1.8GHz MacBook Air with the standard PATA drive fared better.

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