Shoppers spent more time browsing and purchasing gifts on their smartphones and tablets during the recent holiday shopping season but still relied on old-school desktop computers for most of their Christmas spending blitz.

According to data released Monday by IBM, sales on mobile devices rose by 27 percent in November and December over the same period the previous year. Yet sales made through smartphones and tablets only accounted for about 23 percent of online sales overall, with 77 percent of sales coming from desktops and laptops.

The findings underscore a key challenge that the retail industry faces as it courts shoppers in an era of rapid innovation. Many retailers are making big investments to build easy-to-use mobile sites or apps to appeal to the tech-savvy shoppers they're desperate to lure, yet they cannot neglect the traditional Web presence that draws the biggest share of shoppers' money.

IBM also studied how social sites Facebook and Pinterest drive retail sales. The analysis found that shoppers who came to a retailer's website through a Facebook post spent an average of $101.38 per order, while those who came from Pinterest spent $105.75. Jay Henderson, director of IBM Smarter Commerce, said a key difference might be that Facebook included a mix of sponsored ads and posts from friends, while Pinterest did not contain ads, a sign that perhaps the more curated, trusted content from friends was more effective at driving sales. (Pinterest began selling ads on Jan. 1, so that could sour some users' experience with the site in the future.)

IBM found that total online sales were up 13.8 percent in the 2014 holiday season compared with the 2013 season, an uptick that was about in line with the 15 percent growth IBM had predicted. The increase was significantly larger than the 8.5 percent online sales increase recorded by IBM in 2013.

While sales were up overall in the 2014 season, order value was down 8 percent from 2013, with the average order costing $119.33. Henderson said the decline probably stems from shoppers spreading their buying throughout November as retailers kicked off their Black Friday sales long before Thanksgiving weekend.

"The key days all grew: Cyber Monday, Black Friday. But the growth that drove the numbers higher than last year was really coming from other days," Henderson said. In fact, the weekend before Thanksgiving, Henderson said, IBM tracked a 19 percent increase in online sales.

The lower average transaction value could also be related to the bounty of free shipping offers over the holiday season. Experts say these offers can prompt shoppers to "unbundle" their orders, spreading out their purchases over several transactions instead of scooping up slippers for mom and "Frozen" pajamas for the kids in one order.

Among users of mobile devices, IBM found some crucial differences. While smartphones drove about 31 percent of total online traffic, they accounted for 9.1 percent of online sales. Tablets, meanwhile, had a smaller share of overall online traffic -- 13.4 percent. But they accounted for 13.4 percent of total online sales, a larger share than smartphones.

"We've seen a pretty consistent trend where consumers are using their smartphones to browse and their tablets to buy," Henderson said.