The TI-99/4A had a 16-bit TMS9900 CPU running at 3.0 MHz. ....................................
Although the CPU was a full 16-bit processor, only the system ROMs and 256 bytes of scratchpad RAM was available on the 16-bit bus. All other memory and peripherals were connected to the CPU through a 16-to-8-bit multiplexer, requiring twice the cycles for any access and introducing an additional wait state. (This is reportedly due to the failure of a new 8-bit processor being designed by TI for this system, the 9900 processor was already in production and proven.) ..........
.................................
All accesses to the VDP system were executed 8 bits at a time. ....................
The unusual architecture of the 99/4 series is documented to be due to the failure of the 9985, an 8-bit processor which was being created especially for the machine. When it was abandoned, the 16-bit 9900 was selected to replace it, and a great deal of 'glue logic' had to be added to fit the processor into the existing design, while no changes were made to take advantage of the 9900's strengths.