Apple has completed the revamp of its desktop line this week by "speed bumping" its G4 range of professional machines.

For the first time, the quartet of Power Macs features processors running at 1GHz, with the top two models boasting dual 1GHz chips.

This may sound slow compared to chips from Intel and AMD which have now hit the 2GHz mark. But Apple claims that the unique design of its chips means a 1GHz PowerPC chip carries out many tasks faster than its 2GHz rivals.

The company says Adobe's popular picture editing software, Photoshop, runs 70% faster on a 1GHz Mac than on a 2GHz Intel Pentium 4, while video encoding is 300% faster.

The basic Power Mac G4, at £1149 plus VAT, has a single 800MHz processor, with 256MB of memory and a 40GB hard drive. However, it has only a CD-RW drive, rather than the DVD-R/CD-RW SuperDrives drives fitted as standard on all the other Power Mac machines, and on the top-end iMac announced earlier this month.

The mid-range 933MHz Power Mac has a 2MB level 3 cache, which improves performance, and a 60GB hard drive. It costs £1699 plus VAT.

The top-end dual 1GHz model comes in two versions. One, at £2,199 plus VAT, has 512MB of memory and an 80GB hard drive as standard. The other, at £2,679 plus VAT, has 1.5GB of memory and two 80GB hard drives. Both have two 2MB level 3 caches, and are available now.