It could sometimes be difficult to avoid a race condition between a game and the raster display. Flicker could result from the processor writing to the image while it was being sent to the CRT. Therefore, the Macintosh provided a choice of two images in memory, so one could be read while the other was written. The "page" was selected by a general-purpose I/O output connected from the 6522 to the video DMA. As two images added up to 42.75 KiB of precious RAM, however, this feature was unpopular.