Seagate has begun shipping a razor-thin 2.5-inch hard disk drive that the company says is the world’s slimmest.

The GoFlex Slim external hard drive is only 9 millimeters thick. The product shows that hard drives continue to evolve at a regular rate as advances in technology deliver on faster, cheaper, and smaller storage that we have become spoiled by.

The 320-gigabyte version of the GoFlex Slim sells for $99.99 on Seagate’s web site and at select online retailers. The device will be used as an external drive for laptops and netbook computers. The drive is 38 percent leaner than current GoFlex drives and is roughly the width of a pencil. You can fit it in a pocket, purse or messenger bag.

It has a 7200 RPM drive and a universal serial bus (USB) 3.0 interface for fast transfer speeds. It works with Windows or Mac computers interchangeably. A Mac version will be available for Mac OS X computers, making it fully compatible with Apple Time Machine backup software. The drive has enough capacity to hold music collections or carry digital versions of movies.