384Gb is 256Gb + 128Gb or 3 * 128Gb - simple powers of two stuff going on here to arrive at 384Gb.
284Gb is 256Gb + 16Gb + 8Gb + 4Gb - or - 256Gb + 32Gb - 4Gb where the 4Gb is used for something such as video ram.
That is not simple powers of two.
384Gb is 256Gb + 128Gb or 3 * 128Gb - simple powers of two stuff going on here to arrive at 384Gb.
284Gb is 256Gb + 16Gb + 8Gb + 4Gb - or - 256Gb + 32Gb - 4Gb where the 4Gb is used for something such as video ram.
That is not simple powers of two.