You've probably heard me proclaim that the PC is dead. It's a storyline The Motley Fool has been following for years, and it's quite a controversial one among Foolish readers. Just for clarification, keep in mind that when we say "dead," we don't mean it literally. Rather, "dead" refers to the PC stepping aside as the primary computing form factor while worldwide shipments contract.

Each quarter, IDC releases its estimates on the smartphone, tablet, and PC markets. Earlier this month, the market researcher blamed Microsoft (NASDAQ:MSFT) Windows 8 as a major factor leading to the unprecedented 14% drop in worldwide unit shipments in the first quarter. IDC typically waits to release its smartphone and tablet estimates until after Apple (NASDAQ:AAPL) reports earnings, since the Mac maker saves everyone some trouble by actually disclosing unit volumes (unlike most of its rivals).

With these figures in hand, investors can get a comprehensive look at the overall computing market, which includes all three form factors.

Source: IDC.

When looking at the broader computing market through this lens, the PC as a form factor has just hit a new low. PCs are now just 22% of all computing devices.

Source: IDC.

Invariably, many will argue that it's inappropriate to compare PCs to mobile devices, since PCs are still needed for productivity demands. This argument is only true to a certain extent. Even though PCs are truly needed for productivity, enterprise PC upgrade cycles aren't frequent enough to sustain the entire market.

That's especially true considering how poor Windows 8 is doing in the enterprise. Forrester Research released a report last week that estimates that just 2% of surveyed IT pros are upgrading to Windows 8 from Windows XP, while 69% are opting for Windows 7.

Meanwhile on the global front, many regular consumers in emerging markets can only afford one device for casual computing needs. These consumers are opting for mobile devices instead, which is why Apple and its mobile rivals are increasingly focusing on developing countries. Apple is hitting a ceiling, but fortunately Tim Cook is well aware of this and is about to do something about it.

The PC just hit a new low, but it'll keep heading lower.