the GPU frequently overheating in early motherboard models, Microsoft revised the GPU heat sink in order to eliminate thermal throttling. Memory and system bandwidth The console features 512 MB of GDDR3 RAM clocked at 700 MHz with an effective transmission rate of 1.4 GHz on a 128-bit bus. The memory is shared by the CPU and the GPU via the unified memory architecture. This memory is produced by either Samsung or Qimonda. According to Mark Rein of Epic Games, Microsoft had originally planned on using only 256 MB of RAM, but the decision to increase it was based on Epic's upcoming Gears of War title. Epic had been arguing for Microsoft to increase the memory for some time, and Tim Sweeney had sent Microsoft screenshots of what Gears would look like at 256 MB, and then at their proposed 512 MB. Shortly thereafter, Epic was the first studio told of new 512 MB size specification and claimed it cost them a billion dollars but felt it was better for gamers. The Xbox 360 has an extensive amount of bandwidth in comparison to its competition; however, this statistic includes the eDRAM logic to memory bandwidth, and not internal CPU bandwidths. The eDRAM internal logic to its internal memory bandwidth is 256 GB/s. The high bandwidth is used primarily for z-buffering, alpha blending, and antialiasing; it saves time and space on the GPU die. Between the eDRAM die and the GPU, data is transferred at 32 GB/s. The memory interface bus has a bandwidth of 22.40 GB/s and the Southbridge a bandwidth of 0.5 GB/s. Audio and video All games made for the Xbox 360 are required to support at least Dolby Digital 5.1 surround sound. The console works with over 256 audio channels and 320 independent decompression channels using 32-bit processing for audio, with support for 48 kHz 16-bit sound. Sound files for games are encoded using Microsoft's XMA audio format. An MPEG-2 decoder is included for DVD video playback. VC-1 or WMV is used for streaming video and other video is compressed using VC-1 at non-HD NTSC and PAL resolutions or WMV HD. The Xbox 360 also supports H.263 and H.264 MPEG-4 videos. Unlike the original Xbox, voice communication is handled by the console, not by the game code, allowing for cross-game communication. There is no voice echo to game players on the same console; voice only goes to remote