the end of the current line, then write to the register that triggers the synchronization delay via RDY, throwing away a variable amount of CPU time for the benefit of easier video timing synchronization. In addition, the TIA only semi-automatically generates vertical sync timing signals (to mark the end of each video frame and the start of the next). The TIA is capable of inserting a vertical sync signal into the analog output video signal, but it does not have a frame line-counter and so cannot tell when a frame should end. Instead, it is left to the CPU program to trigger vertical sync signals and to count the lines in each frame to determine when a vertical sync signal should be generated. Like for the RDY-wait hardware, the vertical sync signal is triggered by the CPU writing to a specific TIA register address. If no write to that address was ever done and the TIA was allowed to free-run, it would generate a single infinite frame of active raster lines, which would typically appear on the TV as a rolling picture. Most published games for the Atari 2600 generated vertical sync after either every 262 or every 263 lines (but nothing about the TIA prevents it from generating frames of any length, shorter or longer, though the resulting video displays would roll vertically on normal TVs). These and other details of TIA programming mean that programmers need to time their programs carefully to run in the exact number of cycles needed for various screen-related events. Getting this wrong means the screen is not drawn properly. The part of a program that does this is known as the "kernel" of that program. Given this complexity, early games using the system tended to be simple in layout, using the TIA to create symmetric playfields with players on top. This was the original intention of the system: to run the handful of arcade games Atari had already produced like Tank and Pong. In these cases the playfield data was typically laid out in the 2 kB ROM memory in the game cartridge. As each line used 20 bits of data, and there were 192 lines on an NTSC display, a display with a different layout on every line needed only 480 bytes (192 x 20 / 8) of the cartridge's 4 kB to hold a single hard-coded display. In this case the