Tablet Makers Gear Up for Latest Skirmish SAN FRANCISCO - The race for the tablet market has become a full-blown sprint. The intense competition will be highlighted on Tuesday, as Apple, Nokia and Microsoft each introduce new tablets. Those devices will be competing for consumer attention against several others recently released by other tech heavyweights, including Amazon, Google and Samsung Electronics. The stakes are high, and getting higher, as demand for tablets has exploded in the last few years. About 120 million tablets were shipped in 2012, nearly seven times as many as in 2010, when the Apple iPad was first released and generated wide interest, according to Gartner, a market research company. "Getting on an airplane it's amazing the number of iPads that you now see that used to be either notebooks or portable DVD players," along with smaller tablets and e-book readers that are replacing books and magazines, said Ross Rubin, an independent analyst for Reticle Research. Apple has maintained a clear lead, but with the tablet offerings from manufacturers almost as abundant as those for smartphones, the market has become more fractured. In the second quarter, iPads had the largest share of the worldwide tablet market, with 32 percent, according to IDC. Samsung, the No. 2 tablet maker, is quickly gaining traction, with 18 percent of the market in the second quarter, up from 7.6 percent in the period a year earlier. Apple is expected to announce significantly upgraded versions of its iPad and iPad Mini devices on Tuesday. The iPad Mini is expected to have a higher-resolution display, while the bigger iPad is expected to have a slimmer design, weighing about a pound. Both iPads will also most likely get Apple's new processors, but not the fingerprint sensor that is in the latest high-end iPhone. On the same day, Microsoft will release new versions of its Surface tablets. Nokia, the mobile device maker Microsoft is in the process of buying much of, is expected to introduce a new tablet in Abu Dhabi. Mr. Rubin said each manufacturer had developed slightly different approaches with tablets. Microsoft, for example, is largely going after professionals by offering tablets that double as PCs. Samsung sells a large variety of tablets, some that include a stylus for drawing and taking notes, to cater to different professions and interests. And Apple markets its iPads as versatile devices that can be used for both work and play. Amazon offers low-priced tablets to get people to buy content from its stores - one of several less expensive tablets that have emerged to challenge the iPad. Amazon's Kindle Fire costs as little as $140, and Google's Nexus tablet starts at $230. Apple's iPad Mini starts at $330. Many new tablets have already failed or struggled. Hewlett-Packard's TouchPad tablet was killed after 48 days of slow sales. BlackBerry's PlayBook was a dismal failure. And Microsoft's first Surface tablets, released last year, sold so poorly that the company took a $900 million write-down for unsold inventory. Some of the tablets may not be catching on because people are not finding them very useful. A Gartner survey found that 80 percent of people with iPads use their tablets at least 10 times a day, much more often than people with other kinds of tablets. That gives iPad owners more time to be exposed to buying more apps, movies and games. And the more apps they buy, the more likely they will keep buying Apple hardware in the future. "Other tablet providers need to understand why owners of their tablets spent significantly less time on their devices," said Annette Jump, research director at Gartner. Despite the difficulties of breaking into the market, device makers push hard, knowing that future profits could depend in large part on tablet sales. That is especially true for companies like Hewlett-Packard and Microsoft, which have traditionally been closely tied to the PC market. Sales of PCs have softened considerably in recent years, and one reason is that consumers have turned to more mobile tablets for basic computing tasks, like Web surfing and casual game playing. That trend is expected to accelerate. Gartner predicts tablets will outship PCs on an annual basis in two years. About 184 million tablets will be shipped in 2013, Gartner says, versus 303 million PCs. But by 2015, manufacturers will ship 331 million tablets and 272 million PCs. Timothy D. Cook, the chief executive of Apple, remarked on the rapid growth of the iPad in an earnings call last year. "Just two years after we shipped the initial iPad, we sold 67 million," Mr. Cook said. It took us 24 years to sell that many Macs, and five years for that many iPods, and over three years for that many iPhones. For now, at least, Apple continues to be the standard to beat. "It's the reference point," said Mr. Rubin of Reticle Research. It was a pioneer in making tablets more popular and more accessible. Even Apple, though, faces challenges, particularly in emerging markets. In China, for example, generic unbranded tablets that are occasionally knockoffs sell for as little as $80 and are extremely popular. Yet there is a bright side for Apple in China: the Chinese are buying either the cheap white-box tablets or an iPad, not much in between, according to Carolina Milanesi, research vice president at Gartner. In such a fast-changing market, however, that could quickly change. What appears certain is that consumers will be hearing much more about tablets this fall, and particularly this week. "A new iPad launch always piques consumer interest in the tablet category," Tom Mainelli, a research director at IDC, said in a statement. And traditionally that has helped both Apple and its competitors.