A factory in Taiwan reported to work only for BlackBerry maker RIM has closed down, prompting speculation that demand for the PlayBook tablet is weaker than anticipated.

Taiwanese media reported today that Quanta Computer, the world’s largest laptop manufacturer, was closing one of its factories, leading to 1,000 job cuts. Quanta confirmed the job losses.

According to a research note from Arthur Liao, an invesmtent analyst at Hong Kong bank Fubon, the factory in question was dedicated to RIM.

Observers have speculated that the closure reflects weak demand for RIM’s PlayBook tablet. 

Fubon’s Liao estimates that Quanta manufactured 1.5 million of the devices during the first half of the year, while Taiwanese newspaper Digitimes cites unnamed sources as saying that only 800,000 shipped during that period – a discrepancy of 700,000 units.

RIM itself had predicted 4 to 5 million PlayBook shipments for the year.

By way of comparison, Apple shipped 4.4 million iPads during the second quarter of 2011 alone, according to research firm IDC. IDC predicts that Apple will sell 22 million units in 2011 as a whole.