Why the original Macintosh had a screen resolution of 512×324
(512pixels.net)
Many classic Macs came with — or supported — displays running at 512×384 pixels, but many compact Macs, ranging from the original 1984 machine up through 1991’s Macintosh Classic II had built-in CRTs running at 512×342 pixels. That covers all black-and-white compact Macs with a 9-inch screen. The later Color Classic and Color Classic II used a 10-inch CRT at a full 512×384.
Many classic Macs came with — or supported — displays running at 512×384 pixels, but many compact Macs, ranging from the original 1984 machine up through 1991’s Macintosh Classic II had built-in CRTs running at 512×342 pixels. That covers all black-and-white compact Macs with a 9-inch screen. The later Color Classic and Color Classic II used a 10-inch CRT at a full 512×384.