k to a business model based on paying for downloaded games over the internet stored on local memory. The assumption must be that this model also now evolves into just downloading games on demand as and when needed, effectively cloud-based gaming. Similarly, the Microsoft X box is evolving into a dual-purpose entertainment platform that can either store record and play TV programmes and/or download games from the internet. The X Box therefore needs a substantial amount of hard-disk space of the order of 250 GB. A desk-top hard disk is typically now a three and a half inch diameter device spinning at between 10 000 and 15 000 rpm. The capacity in 2005 was typically 100 GB. Six years later capacity is typically somewhere between 750 and 1000 GB (one terabyte). The power budget of these devices (8 to 10 W) precludes their use in portable products. Lap tops typically use two and a half inch diameter hard disks offering 250 GB of capacity. A spin speed of 10 000 rpm produces a seek time of under 5 milliseconds but power consumption is still over 5 W. Reducing the spin speed to 5000 rpm increased the seek time to about 15 milliseconds but reduces the power to about 3 W. In 2005 iPods used 1.8-inch hard disks with between 20 and 60 GB of storage and a variable 3990 to 4200 rpm spin speed. Power consumption was about 1.3 watts but as with other portable products solid-state memory has taken over. In 2005 vendors were promoting either 1-inch drives (Hitachi) or 0.8-inch 'microdrives' (Toshiba and Samsung) for cellular phones. The one-inch drives fitted into a Type 2 PC card form factor (5.2 mm) and weighed 16 g. Microdrives had a depth of 3.3 mm and weigh 10 g. One-inch disks typically held about 8 to 10 GB and microdrives were either 2 or 4 GB. Both had a spin speed of 3600 rpm giving a seek time of 12 to 15 milliseconds and a transfer rate of 4 or 5 M/bytes per second. A one inch drive had a power consumption of just under one watt, a 0.85-inch drive, about 700 milliwatts. Some cellular handsets became available with har