Texas Instruments TI99/4A

I made this page because the TI99/4A initiated the design and production of the DAI computer.
All the TI stuff was borrowed from Lino Lampers. Thanks Lino!

The machine TI99/4A console A lot of info on the TI99/4A is available. So only some highlights are here, with links to sites with more information.

The TI99/4A was the only 16 bit computer for the home market in 1980, the time it was launched. The data bus is 16 bits wide, but only the CPU RAM (256 bytes) and ROM (8 kBytes) supported this. All other peripherials were 8 bits wide. The video processor had 16 kBytes available, which was also used to store BASIC programs. The main processor could access this memory only through a memory mapped port. The computer also contained about 18 kBytes of GROM, special ROM containing the graphics routines written in GPL, a special interpreted graphics language. These GROM devices were only accessible through a memory mapped port. Games were typically GROM based and written in GPL.

The design made the computer very slow in BASIC, and with only 256 bytes RAM, no serious machine code assembly was possible.

one GROM
content of a typical cartridge

The basic TI99/4A was just a games console, with lots of games available. The BASIC seems to be added to give it some educational value, which probably helped sales. Few people buy a games console for their children, but a real computer with BASIC, and a games option, seemed a good compromise. The GROMs in the cartridges were propriatairy TI and mandatory in cartridges, so the manufacturer profited from every game sold.
The typical cartridge contents was very simple, and cheap to produce. Eventually a replacement schema consisting of an standard Eprom and some shift registers was created, so people could create their own cartridges or copy existing ones.

mini memort cartridge

peripherial interface with 32 kByte RAM
on top

For assemby programmers several options were available:
  • the 'Mini Memory' cartridge contained an assembler and extra CPU RAM,
  • the complete assembler package also required the disk system which consisted from a cartridge, the disk controller, the disk drive, and extra RAM. The latter three could be placed in the Peripherial Box.

    The disk controller was build around the WD1771 FDC, which supported single density only, the 5 1/4" disk drives were 40 track single sided. So storage capacity was limited to 89 kBytes per disk. Up to three drives could be connected. The newer "Disk Manager 2" cartridge supported double sided drives.

  • TI with peripherial box console with peripherial box

    The required extensions for the TI99/4A to work with assembler and disk drives was so expensive, only game developers bought it. There is a clear distinction in the way the components are manufacturered; the console and cartridges are cheap mass products, the peripherial interface and the extension cards in it are build for eternity. They look like high end mini or mainframe components. (Maybe TI reused existing components from their business computer systems for the 99/4A).

    Generic links:

    Updated: 2012-10-02