and so these graphics modes are not popular outside of demos. Effective use of the GTIA color interpretation feature with text modes requires a carefully constructed character set treating characters as pixels. This method allows display of an apparent GTIA "high resolution" graphics mode that would ordinarily occupy 8K of RAM to instead use only about 2K (1K for the character set, and 1K for the screen RAM and display list.) The GTIA also fixed an error in CTIA that caused graphics to be misaligned by "half a color clock". The side effect of the fix was that programs that relied on color artifacts in high-resolution monochrome modes would show a different pair of colors. Atari owners can determine if their machine is equipped with the CTIA or GTIA by executing the BASIC command POKE 623,64. If the screen blackens after execution, the machine is equipped with the new GTIA chip. If it stays blue, the machine has a CTIA chip instead. Bugs The last Atari XE computers made for the Eastern European market were built in China. Many if not all have a buggy PAL GTIA chip. The luma values in Graphics 9 and higher are at fault, appearing as stripes. Replacing the chip fixes the problem. Also, there have been attempts to fix faulty GTIA chips with some external circuitry. See also List of home computers by video hardware References External links De Re Atari published by the Atari Program Exchange Mapping the Atari, Revised Edition by Ian Chadwick GTIA chip data sheet scanned to PDF. jindroush site(archived) GTIA info CTIA die shot GTIA die shot Atari 8-bit family Graphics chips Integrated circuits Computer display standards