Shares of Apple (AAPL -2.19%) have been particularly weak of late, even officially entering correction territory by pulling back over 10% earlier this week. Despite that softness, Apple has proceeded to hit a new high. Huh?

You got some 'splainin to do
We're talking about PC market share figures, of course! Market researchers Gartner and IDC have now released their respective estimates of the broader PC market, and the figures show that Apple has now reached a new high with its domestic market share. The estimates vary slightly, but Gartner pegs the Mac maker's domestic share at 13.6%, with IDC perched at 12.5%.

Here are the top five for Gartner's domestic digits:

Company

Q3 2012 Shipments

Q3 2012 Market Share

Shipment Growth (YOY)

Hewlett-Packard (HPQ -2.00%)

4.1 million

27.0%

(19.3%)

Dell (DELL.DL)

3.3 million

21.4%

(15.9%)

Apple

2.1 million

13.6%

(6.1%)

Lenovo

1.4 million

8.9%

6.1%

Acer

989,000

6.5%

(28.2%)

Source: Gartner.

For comparison, here is IDC's top five:

Company

Q3 2012 Shipments

Q3 2012 Market Share

Shipment Growth (YOY)

HP

4.3 million

26.1%

(18.8%)

Dell

3.4 million

20.7%

(16.0%)

Apple

2.1 million

12.5%

(7.0%)

Lenovo

1.4 million

8.3%

9.2%

Acer

1 million

6.1%

(19.6%)

Source: IDC.

Apple still lags HP and Dell by a fair margin, and HP even lost its crown as the top PC vendor on a worldwide scale. That title now belongs to Lenovo.

According to Gartner, the overall domestic market shrank by 13.8% to 15.3 million units. Analysts noted that the third quarter is typically boosted by back-to-school sales, but this time around things were different. Domestic shipments didn't even increase sequentially, and enterprise shipments are also slowing. The concern there is that peak upgrade activity in the enterprise market has already come and gone.

Domestic sales were far weaker than expected. IDC thought the market would shrink just 9.5%, but its figures posted a 12.4% drop.

What's to blame?
There are two key contributing factors the weakness in the PC market: Microsoft (MSFT -1.96%) Windows 8 and tablet adoption. This was the final full quarter preceding the massive launch of the software giant's next-generation operating system. Virtually all PC players (excluding Apple, of course) are banking on Windows 8 to reinvigorate PC sales and some purchasing delays immediately ahead of the launch are expected.

Tablet sales, led by the iPad, continue to cannibalize PC sales, and even Apple is susceptible there, as Mac shipments also declined. The threat of tablets is why Intel (INTC 1.74%) has been making a big push with Ultrabooks, but unfortunately this initiative has been underwhelming thus far. The chip giant was hoping that by year's end, Ultrabooks would account for 40% of consumer notebook sales.

The category has severely underperformed expectations, and IHS iSuppli has now dropped its full-year Ultrabook forecast by half to just 10.3 million. The two primary hurdles that Ultrabooks are facing are high prices and confusing marketing. While Ultrabooks are modeled after Apple's MacBook Air, the MacBook Air continues to dominate the market for thin and light laptops and isn't classified as an Ultrabook.

Dire PC sales are why Intel isn't expected to put up any revenue growth this year, since its processors bound for consumer PCs continue to be its largest segment. The PC client group was 69% of sales last quarter, and Intel's also waiting on Windows 8 for entry into the tablet market.

If investors thought the second-quarter numbers were proof that Wintel needs Windows 8 posthaste, then the third-quarter figures should hammer home that point beyond any shadow of a doubt.