The Spectrum 128 was the second model of Spectrum; the main improvements over the base model were 128Kb of RAM and an AY-3-8912 sound chip. The comp.sys.sinclair FAQ contains detailed information on the Spectrum 128, but contains a number of errors/omissions: * Reading from port 0x7ffd does produce an effect: the value read (generally the floating bus value) is written back to port 0x7ffd. (This effect does not occur on the +2A/+3). * Contended IO does apply to ports in the range 0xc000 to 0xffff if a contended memory page is currently paged in.