According to MediaGuardian, the research firm has slashed its prediction for the number of PCs that will be sold this year from 363.5m to 352.4m, and that figure may yet fall further.
The drop is part of a longer-term trend, according to Ranjit Atwal, Gartner's research director: "Over the longer term, media tablets are expected to displace around 10 per cent of PC units by 2014," he predicts.
Gartner also predicts that by 2013, 80 per cent of businesses will support tablet computers for their staff.
Last week, Citigroup forecast that 35 million tablet computers, including 26 million iPads, will be sold in 2011.