ocr: MEMORY ARCHITECTURE (Continued) MMU and I/O Memory Organization The block of memory represented by the VO Block is an expanded view of the memory block entitled I/O + CHAROM, as shown in the C128 memory map. When the 1/O block exists, access to VIC, SID, and I/O, as well as the addition of the MMU can be accomplished. All 1/O functions remain as they were previously on the C64 with the exception that the MMU and the 80 Column chip have been added. With the exception of four registers that are asserted in the zero page in C128 mode, all new MMU registers appear in an unused slot in the I/O Memo ...