MSX Village forum

When the MSX is operating under BASIC, all instructions processed by the processor must be fetched from the BASIC ROM. To prevent that the R800 gets slowed down too much under BASIC, a very smart trick has been used. The MSX turbo R reset routine copies the entire BASIC ROM into the four highest pages of the internal RAM memory and switches to the so-called DRAM mode after doing so. In this DRAM mode, the four highest pages of the internal memory are not any more visible in the RAM slot. Instead, they are visible at the locations where you would expect to find the BASIC ROM. Because of this, all BASIC interpreter instructions will be fetched from fast DRAM memory in stead of slow ROM memory. Consequently, the BASIC interpreter will run faster.