TI99/4A
The TI99/4A home computer was introduced by Texas Instruments in June 1979.It had a 16 bit TMS-9900 CPU at 3.3Mhz. This was one of the first 16 bit processors to be made. However, apart from a very small ammount of memory, the processor communicated with the rest of the console using an 8 bit data path. Therefore it was substantially slower than a true 16 bit micro. However, the 16 bits were used to make speech synthesis possible, and could also be used by an experienced programmer to speed up some machine code programs.
Because the machine only had 16kb of RAM the TI99/4A's coprocessor, a TMS-9918, had its own RAM referred to as VDP RAM (visual display processor RAM). This 16k of memory could not be directly addressed by the CPU. The VDP was used to provide sprite support.
The VDP RAM was used for screen display, variables, and user program which the main processor cannot directly address. Data was tranferred between the VDP and the CPU two bytes at a time, which did not serve as a particularly fast means of communication and no doubt contributed to the slow speed of the 4A.
As there was no realistic ammount of RAM addressable by the CPU, machine code programs would not run unless more RAM was added in the form of either the 32k expansion card or the 4k mini memory module.
The CPU, motherboard, and cartridge drive were built into a single unit with the keyboard.
Peripherals included a 5ÃÂü" floppy disk drive, an RS-232 interface and a 32kb memory expansion card.