How Apple's Fusion Drive speeds up iMacs

New iMacs will offer 'Fusion Drive,' a way to boost speed without losing storage. The Apple desktops will ship out to customers on Nov. 30.

Apple's new iMac line ships on Nov. 30.

When Apple unveiled its latest iMac desktop in October, it also introduced a clever way to speed up computers in general. Shoppers can pay a little extra for an iMac with two storage drives: a traditional hard drive and a solid-state drive.

The latter – sometimes called a flash drive – is much speedier than normal hard drives. Performance tests by Computerworld show that solid-state drives can run up to 3.7 times faster. Apple says booting up an iMac with a built-in flash drive takes less than half the normal time.

Because of this significant speed boost, several computer companies, including Apple, have started to phase out hard drives and focus on flash drives.

But there's a catch. Solid-state drives are expensive, especially for any that can hold more than 100 gigabytes. Phones and tablets can get away with topping out at 64 gigabytes of all-flash storage. But the price can become prohibitive for laptops and desktops. Apple charges $300 to upgrade a MacBook Air's 128-gigabyte flash drive to 256 gigabytes. Meanwhile, many people expect modern desktops to offer several thousand gigabytes. That much solid-state storage could double the price of a computer.

So rather than sacrifice the speed of a solid-state drive or the high capacity of a hard drive, Apple will now use both. Top-of-the-line iMacs will include a zippy 128-gigabyte flash drive for the programs that people use most often and a 1- to 3-terabyte hard drive for music, videos, and documents.

Apple borrowed this idea from power users, such as hard-core PC gamers who will put the latest, greatest video game on a flash drive for maximum performance and then move it to a hard drive when the next big game arrives. This trick never really took off. It required people to rig up two different drives on their own and to constantly swap files from one to the other.

Apple has streamlined the process. Its Fusion Drive software notes which programs you use most often and automatically moves them over to the flash drive.

Some Ultrabooks come with the Windows operating system on a solid-state drive, and general PC owners can add their own all-in-one "hybrid drives." and both sell several options from Western Digital and Seagate. Prices start around $70 for a combined 500-gigabyte drive.

For more on how technology intersects daily life, follow Chris on Twitter @venturenaut.

[Editor's note: This is an updated version of an article that appeared in the November 19 issue of the Monitor weekly magazine.]

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