Apple II Graphics

The Apple II graphics were composed of idiosyncratic modes and settings that could be exploited. This graphics system debuted on the original Apple II, continued with the Apple II Plus and was carried forward and expanded with the Apple IIe, Enhanced IIe, IIc, IIc Plus and IIGS.

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 PC-compatible machines) had 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).

All Apple II machines featured an RCA jack providing a rough NTSC, PAL, or SECAM composite video output (on non-NTSC machines before the Apple IIe this output is black-and-white only). This enabled the computer to be connected to any composite video monitor conforming to the same standard for which the machine was configured. However the quality of this output was sketchy; the sync signalling was close enough for monitors—which are fairly forgiving—but did not conform closely enough to standards to be suitable for broadcast applications, or even input to a video recorder, without intervening processing. (The exception was the Extended Back version of the Bell & Howell branded black II Plus, which did provide proper video sync, as well as other media oriented features.)

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