Q4, which includes the holiday shopping season, was good to many industries last year – but the PC industry wasn’t one of them.

According to IDC, some of the biggest PC manufacturers, including HP, Dell and Acer, recorded declines in sales.

Performance was so bad that IDC described 2011 as “the second-worst year in history” for PCs, as total sales declined 5% from 2010.

Gartner’s numbers largely mirrored IDC’s. According to Gartner, global PC shipments dropped 1.4% in Q4, and experienced a paltry 0.5% rise during the entire year. The research firm cited “continuously low” demand as the culprit.

Low demand for PCs was good news for Apple, however, which, saw 18% growth in the number of Macs it sold, giving Apple a double-digit (nearly 11%) share of the desktop computer market in the United States.

So what gives? Is this the new normal, as PCs compete against Macs, more powerful smart phones and tablets?

While a hard drive shortage late in the year shouldn’t be ignored, the answer to that question appears to be ‘yes, at least to some degree. Consumers simply have more choices when it comes to computing devices, and a bulky new PC isn’t always the most appealing choice.

Increasingly, however, that may not matter to the large PC manufacturers watching as their PC shipments decline.

Sure, Windows 8 might offer a small amount of hope for PCs in 2012, but companies like HP, Dell and Acer are increasingly branching out, prepping tablets and ultrabooks.

In other words, PC manufacturers aren’t just manufacturing PCs anymore. The question is whether the strong competition from Apple and new entrants like Amazon will allow them to sell enough tablets and ultrabooks to offset the decline of the desktop PC.