Apple sold a record 5.75 million Macs in the quarter that ended Dec. 31, an increase of 19% that beat the overall industry by a wide margin, IDC said Monday.

In a preliminary estimate, IDC pegged Apple's sales for 2014's fourth quarter at 5.75 million, a record for a three-month period. According to IDC, Apple sold 4% more Macs than the previous quarter, currently the record.

If U.S. retail sales are any guide, the Mac's jump came primarily from its lower-priced laptop, the MacBook Air. "Apple had about a third of all notebook sales below $1,000 in the 14 weeks of the fourth quarter," said Stephen Baker, analyst with the NPD Group, another research firm. "That number was only 8% in 2013."

Meanwhile, IDC tapped global personal computer shipments for the fourth quarter at 80.8 million, representing a 2.4% decrease from the same period in 2013. Mac shipments accounted for 7.1% of all personal computers worldwide, putting Apple in fifth place behind Lenovo, Hewlett-Packard, Dell and Acer.

For the year, IDC estimated that Apple sold 19.8 million Macs, or 15% more than the current annual record set in 2013.

Rival researcher Gartner, which also issued estimates Monday, didn't have Apple in its top five OEMs (original equipment manufacturers) for either the fourth quarter or all of 2014. Instead, the firm had Acer, with 6.3 million machines, and Asus, with 22.8 million, as the fifth-largest vendors for the quarter and year, respectively.

Gartner's take was more optimistic about the personal computer business, saying that it was up 1% in the fourth quarter.

The two research firms tally different kinds of machines beyond traditional desktops and notebooks, which was reflected in their out-of-sync numbers: IDC counts Chromebooks but not devices with detachable keyboards, like Microsoft's Surface Pro 3, while Gartner does not include Chromebooks but does count Windows tablets.

Baker of NPD was impressed with Apple's sales, which he had finalized only for notebooks as of late Monday. "Having a nice increase on top of really strong comparable numbers [of 2013's fourth quarter] is a pretty impressive performance," Baker said in an interview.

He tapped the MacBook Air as Apple's bestseller in U.S. retail, especially the models under $1,000. Apple sells two such laptops, an 11-in. model that lists for $899 and a 13-in. model for $999.

The brisk sales and the lower prices of the MacBook Air in 2014 -- Apple cut prices between 8% and 10% in April -- had an impact on the bottom line as well. Baker's retail estimate had Apple's notebook revenue down 3% year-over-year even as sales volume was up double that. "The lower prices paid off in more units, but they had to give up a little revenue," he said.

The ASP, or "average selling price," of a Mac notebook in the quarter was $1,289, down 8% from the year prior.

Baker expected that the Mac laptop ASP will climb in 2015 if, as rumors have claimed, Apple releases a Retina-equipped MacBook Air during the year. That chatter has focused on a 12-in. higher-resolution screen, which would fall between the current 11-in. and 13-in. models, possibly replacing one or both.

Baker thought otherwise. "If they do Retina on the Air, it will look like what the MacBook Pro looked like," Baker said. "Apple will try to get people to buy up."

He was referring to Apple's pricing strategy of 2012, when it launched the first Retina MacBook Pro. Then, Apple simply inserted a new model -- a 15-in. MacBook Pro with Retina -- into the line at a price $400 higher than the lowest-priced 15-in. stock model. The existing laptops' prices were retained and their prices did not change. Only later did Apple add Retina to other MacBook Pros.

Other analysts thought the Mac, even after setting sales records in 2014, still had a substantial upside. "In 2015 we will absolutely see a quarter where Macs get above 6 million," tweeted Ben Bajarin of Creative Strategies after IDC published its estimates. "Apple is poised to keep gaining share of the PC market."

According to IDC, global personal computer shipments in 2014 were down 2% from the already-dismal 2013; Gartner, on the other hand, pegged shipments as essentially flat for 2014.

Apple will disclose its fourth-quarter Mac sales numbers on Jan. 27, when it holds its next earnings call with Wall Street.