In these character modes each pair of bits in the character glyph represents a pixel one color clock wide, thus a single byte of glyph information represents 4 pixels rather than the 8 pixels of other modes. The character set uses 128 characters and requires 1024 bytes of RAM. The background color is . This mode allows up to four colors (including the background) to be displayed in one character matrix. If the high bit of the character value is set (i.e. inverse video) then a fifth color, , is displayed in place of the pixel bit pattern "11" that ordinarily shows . The color choices based on the bit pairs of the character glyph: Map Modes GTIA Modes GTIA modes are Antic Mode F displays with an alternate color interpretation option enabled via GTIA register PRIOR ($D01Bhex/53275dec) shadowed by GPRIOR ($026Fhex/623dec). The full color expression of these GTIA modes can also be engaged in Antic text modes 2 and 3, though these will also require a custom character set to achieve practical use of the colors. See GTIA for more information. Scrolling Before video displays became a common part of the user interface many computers used a teletype—a printer usually with continuously-fed paper. User input and the computer generated output were printed on the paper fed through the printer. This widely understood interface for user input and computer output continued with the introduction of video displays as computers presented a metaphor of the screen as a view port over an imagined, infinite roll of paper. Information is displayed on screen beginning at the top until it reaches the bottom of the screen and when the computer needs to introduce new information it shifts all the screen information up providing an empty space at the bottom for the new information and consequently erasing the topmost information. This kind of scrolling is called, "coarse scrolling". It is achieved by moving bytes of memory through a designated screen display area. Moving a kilobyte (or more) of memory is CPU intensive and slower computers may not be able to accomplish anything else while updating screen data. As a means of animating a display the results can be jerky when the CPU cannot update the screen memory faster than the display hardware reads the memory to generate the video output. Motion fluidity is impaired, since the minimum amount of shifting the display is the