According to a survey by Jupiter Research, 1,000 songs (about the capacity of Apple’s iPod mini) is the right size for a portable digital music player. The online survey found that 90 percent of consumers have no more than 1,000 songs on their computers, and that a rechargeable battery, small device size, and the ability to connect the device to their computer were among the features that mattered most to music fans. The survey also found that 20 percent of consumers said playing MP3 files is important, versus 7 percent who prefer files in Microsoft’s WMA format and fewer than 1 percent who prefer the Advanced Audio Coding (AAC) format used by the iTunes Music Store.