which can produce a variety of symptoms including graphics glitches in Mode 7, a black screen on power-on, or improperly reading the controllers. The first revision 5A22 has a fatal bug in the DMA controller that can crash games; this was corrected in subsequent revisions. The console contains 128KB of general-purpose RAM, which is separate from the 64KB VRAM dedicated to the video and audio subsystems. Video The Picture Processing Unit (PPU) consists of two closely tied IC packages. It contains 64KB of SRAM for video data, 544 bytes of object attribute memory (OAM) for sprite data, and 256 × 15 bits of color generator RAM (CGRAM) for palette data. This CGRAM provisions up to 256 colors, chosen from the 15-bit RGB color space, from a palette of 32,768 colors. The PPU is clocked by the same signal as the CPU and generates a pixel every two or four cycles. Audio The S-SMP audio chip consists of an 8-bit CPU, a 16-bit DSP, and 64KB of SRAM. It was designed and produced by Sony and is completely independent from the rest of the system. It is clocked at a nominal 24.576 MHz in both NTSC and PAL systems. It is capable of stereo sound, composed from 8 voices generated using 8 bit audio samples and various effects such as echo. Regional lockout Nintendo employed several types of regional lockout, including both physical and hardware incompatibilities. Physically, the cartridges are shaped differently for different regions. North American cartridges have a rectangular bottom with inset grooves matching protruding tabs in the console, and other regions' cartridges are narrower with a smooth curve on the front and no grooves. The physical incompatibility can be overcome with the use of various adapters, or through modification of the console. Internally, a regional lockout chip (CIC) within the console and in each cartridge prevents the PAL region games from being played on Japanese or North American consoles and vice versa. The Japanese and North American machines have the same region chip. This can be overcome through the use of adapters, typically by inserting the imported cartridge in one slot and a cartridge with the correct region chip in a second slot. Alternatively, disconnecting one pin of the console's lockout chip will prevent it from locking the console; hardware in later games can detect this situation, so it became common to install a switch to reconnect the