Shipments of Windows RT devices were expected to reach between 4 million and 4.5 million units by the end of 2012. According to Digitimes, vendors are now believed to have shipped half of the original estimates, somewhere around 2 million units, and actual sales are said to be even worse.

Following Microsoft’s (MSFT) announcement of the Surface tablet, some manufacturers gave up plans to release Windows RT devices and only a handful of tablets made it to market. Sales are now estimated to be around 400,000 units. The relatively small selection of applications and high sale prices of devices has made it difficult for Windows RT to compete with other comparable operating systems.

Digitimes notes, however, that Microsoft may soon lower the price of the Surface RT to clear inventories and make room for the Windows 8-based Surface Pro. The company has also reportedly offered incentives for vendors to participate in the development of second-generation Windows RT models, although vendors are said to be unwilling to do so.