Conventional wisdom that may have been true ten years ago, but which has been disproved by every objective* comparison, like versus like, done since Apple went to Intel chips. The difference today is always tiny and can be in either direction. Those who continue to believe this don't make objective comparisons, but simply point to low-end Windows machines that have no Mac equivalents (Apple is not after that market) and say "it's cheaper than Apple." That's true. If one of those meets your needs, buy it.

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*That is, by publications like PC Week, Computerworld and the Wall Street Journal - not exactly hotbeds of Macintosh fandom.