Apple II graphics

Apple II graphics debuted on the 1977 Apple II and was used throughout the Apple II line. They consist of a 16 color low resolution mode and a high resolution mode where visuals are dependent on artifact color. The Apple IIe added "double" versions of each of these, most prominently "double high resolution" with twice the horizontal resolution in 16 colors. Internally, Apple II graphics modes are idiosyncratic and do not simply use a linear frame buffer. The 1986 Apple IIgs split from previous Apple II architecture and the graphics have more in common with the Atari ST and Amiga. The graphic modes of the Apple II series were peculiar even by the standards of the late 1970s and early 1980s. One notable peculiarity of these modes is a direct result of Apple founder Steve Wozniak's chip-saving design. Many home computer systems of the time (as well as today's IBM PC compatibles) had an architecture which assigned consecutive blocks of memory to non-consecutive rows on the screen in graphic modes, i.e., interleaving. Apple's text and graphics modes are based on two different interleave factors of 8:1 and 64:1. A second peculiarity of Apple II graphics—the so-called "color fringes"—is yet another by-product of Wozniak's design. While these occur in all graphics modes, they play a crucial role in Hi-Resolution or Hi-Res mode (see below). Reading a value from, or writing any value to, certain memory addresses controlled so called "soft switches". The value read or written does not matter, what counts is the access itself. This allowed the user to do many different things including displaying the graphics screen (any type) without erasing it, displaying the text screen, clearing the last key pressed, or accessing different memory banks. For example, one could switch from mixed graphics and text to an all-graphics display by accessing location 0xC052 (49234). Then, to go back to mixed graphics and text, one would access 0xC053 (49235).