Do you invest in computer stocks? Get ready for a rocky ride.

Last week, we took a look at a report from Taiwanese PC specialist Compal Electronics, which suggested that investors are about to get sandbagged by a steep falloff in PC sales. As you'll recall, Compal's estimates were forecasting about a 12.5% decline in PC demand. Pretty scary stuff. But guess what?

It might not be so bad as that after all.

Yesterday, researcher Gartner released its version of what the future for PCs will look like, and Gartner painted a considerably prettier picture, at least in the short term. According to the IT specialist, 2011 PC shipments will in fact come in only about 5.5 percentage points lower than previously predicted -- a much prettier picture than the damage Compel computed. Perhaps in response to the news, CNBC reported that semiconductor stocks including SanDisk (Nasdaq: SNDK), Micron (Nasdaq: MU), and Texas Instruments (NYSE: TXN) were among the nimblest performers dodging Friday's sell-off.

Where's the disconnect?
What might explain the mixed signals coming out of these two economic forecasts? Well, the most obvious answer would be that Compal is focusing on forecasts for PCs that it will be shipping for its primary customers, which include Dell (Nasdaq: DELL), Hewlett-Packard (NYSE: HPQ), and Lenovo. Gartner, looking through the wider lens at the whole PC industry, may be noticing greater strength in the sales of makers such as Acer, Apple, Sony, and so on.

Of course, the really good news here is where Compal and Gartner's visions converge. Just a few months down the road, both firms agree that after sales slide 5%, 12%, whatever, in 2011, they're going to rebound quickly in 2012. Here, it's Compal occupying the optimist's camp and predicting a 20% rebound; Gartner is more conservative, predicting an 11% bounceback in 2012.

The upshot for investors
Who's right? Who knows? Maybe 2011 will be really bad for PC sales, or maybe only sorta bad. Maybe 2012 will be a burnburner, like Compal says. Maybe just lukewarm, as Gartner predicts.

Either way, though, if you look past the short-term turbulence, most analysts agree that PC and mobile-chip companies like TI, Micron, and SanDisk should be able to keep profits growing in the low-teens for the next five years. Intel (Nasdaq: INTC) and AMD (NYSE: AMD), likewise. Meanwhile, most of these stocks sell for 10 times earnings (TI, Micron) or less (everybody else).

Sound like an opportunity to you? It does to me.

Want to see how all these predictions play out?