The PSX uses a 16 bit mode (5:5:5:1 R:G:B:A) for it's 3D operations, so the shading functions also had to operate with only 5 bits of intensity. While they were doing this, they also decided to remove an operational restriction that had been imposed by the original design - as I mentioned earlier, the video DAC on the original consoles was driven directly by the VRAM - which also meant that it had to operate in the same bit depth as the framebuffer did. This was effectively a bet that VRAM was going to become mainstream and cheap, which ended up not happening - instead, most video card manufacturers started using SGRAM instead.Īs a result of this, and because the PSX was selling very well, Sony decided to redesign the GPU to use the more readily available SGRAM. When Sony first produced the PlayStation, they used a design for the GPU that used dual-ported VRAM with the video DAC wired directly to the read on the RAM and the other (read/write) port connected to the GPU.
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