A Target shopper uses her iPhone to compare prices at Wal-Mart. (AP Photo/Robert F. Bukaty/AP)

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 last year. And yet sales made through smartphones and tablets still only accounted for about 23 percent of online sales overall, with a whopping 77 percent of sales coming from desktops and laptops.

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

IBM also studied how social sites Facebook and Pinterest drive retail sales. The analysis found that shoppers who came to retailer's Web site through a Facebook post spent an average of $101.38 per order, while those who came from Pinterest spent $105.75.  Henderson 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 a healthy 13.8 percent this holiday season compared to 2013, an uptick that was about in line with the 15 percent growth IBM had predicted.  This year's increase was significantly larger than the 8.5 percent online sales increase recorded by IBM last year.

While sales were up overall this year, order value was down 8 percent from 2013, with the average order costing $119.33.  Jay Henderson, director of IBM Smarter Commerce, said the decline is likely because shoppers spread their buying throughout November as many retailers kicked off their so-called 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 sale.

The lower average transaction value could also be related to the bounty of free shipping offers this holiday season. Experts say these offers can prompt shoppers to "unbundle" their orders, meaning that shoppers may spread 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 only 9.1 percent of online sales.  Tablets, meanwhile, had a smaller share of overall online traffic--just 13.4 percent.  And yet 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.

IBM's report is the latest morsel of early data that suggests the holiday season was a solid one for the retail industry. The Commerce Department reported that November retail sales rose 0.7 percent to $449.3 billion, with nearly every category of retailer recording an increase.  Target said that it saw record online sales over Black Friday weekend; Wal-Mart reported record online traffic on Black Friday, only to beat that record again on Cyber Monday.