The case headed to trial on Tuesday harks back to Apple's pre-iPhone era, when the iPod was its flagship mobile device. Several emails from Apple co-founder Steve Jobs are expected to be entered into evidence, along with short deposition excerpts of Jobs videotaped before he died.
Apple executives including software chief Eddy Cue and marketing senior vice president Philip Schiller are also expected to testify.
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Apple faced a challenge in the online music market from Real Networks, which developed RealPlayer, its own digital song manager, plaintiffs claim. It included software which allowed music purchased there playable on iPods.
In 2006, Apple introduced a software update that barred RealPlayer music from the iPod. Plaintiffs claim that discouraged iPod owners from buying a competing device when it came time to upgrade.
Apple, meanwhile, argues in filings that RealPlayer had less than 3 percent of the online music market in 2006, making it "implausible" that its iTunes update would have had such a huge impact on iPod owners' buying decisions.