A Macintosh (now usually just Mac) is one of a series of computers made by the Apple company. A mackintosh is a style of waterproof raincoat invented in the 1820s by Charles Macintosh (the k was added to the raincoat name almost immediately). A McIntosh is a type of red apple grown primarily in eastern Canada and the northeastern U.S.
Macintosh and McIntosh are proper nouns, meaning the first letter (along with the I in McIntosh) is capitalized. Mackintosh is a common noun, so it is not capitalized. The plurals are Macintoshes, mackintoshes, and McIntoshes.
They take top-boots and Mackintoshes from across the water and caricature our fashions ; they read a little, very little, Shakspeare, and caricature our poetry. [The Corsair (1839)]
Given a roadster of this description, and a light, open wagon fitted with a stout spring, with lamps, and possibly with a small break ; given also a sympathetic companion and a mackintosh … what more delightful than to take the road at any time between April and November! [Atlantic Monthly (1890)]
In 16 years Mr. Davis has changed a profit-less orchard into a prosperous multi-thousand-dollar business in Mcintosh apples. [Life (1949)]
As Apple Computer, Inc.’s Macintoshes infiltrate corporate computering environments currently dominated by MS-DOS-based microcomputers, users are demanding more sophisticated links between the two worlds. [Network World (1987)]
Sure I am ready for Y2K and always have been. I use a Macintosh and the people who designed it must have looked at a calendar and said that their computers are long lived enough to make it well into the new millennium and they are. [letter to BBC News (1998)]
And when he appeared at a university ceremony in 1940, his bare feet and legs suggested that he was naked save for a mackintosh. [Telegraph (2008)]
An unseasonably warm winter and early spring has exposed the trees of New York’s iconic McIntosh apples to a potential crop-killing freeze. [Newsday (2012)]