TI99/4A Comments

Tursi (mbrent@awinc.com) writes:

A comment on the TI section: With memory expansion, you mention that BASIC programs had only 12k. While that's true, under Extended BASIC you got 24k of the 32k expansion for programming, with the other 8k reserved for system and assembly subroutines.

TI BASIC, I feel, did a lot to kill off the ol' machine... not only was it slow, it did not support the TI's powerful (at the time) sprites, nor the 3 other graphics modes (a 40-column text mode, a 64x48 'multicolor' mode, and a 256x192 bitmapped mode [only on the 4A, not the 4]). There was also no support for assembly programming at all, but then, the base console had only 256 BYTES of CPU RAM. The 16k was all video RAM. Extended BASIC gave the extra RAM (if you had it), sprites, and access to assembly (again, if you had expansion RAM).

Also, the expansion box (the ol' PEB) was not required for memory expansion... or any other expansion. TI, and several other companies, made expansion modules that plugged into the side, like the speech synth. Of course, the computer could get very long in a hurry, and I've seen a machine like that. :) Several 'hacks' allowed putting the RAM expansion inside the console, which was also nice.. one put the RAM on the 16-bit bus which effectively doubled the speed of assembly programs.

Doug Ferguson (dferg@planet.net) writes:

Just a few notes on your TI-99/4A article.

  1. The 99/4A was a 16 bit machine. It contained the TMS9900 microprocessor (still in use today as the more advanced TMS9995). The processor could directly access 64K and indirectly access up to 1 MB. The 256 bytes you spoke of were the "fast" ram which resided on the 16-bit bus. All other memory was addressed through the 8-bit bus.
  2. The major slowdown in the 99 was the TI Graphics Program Language chip set. This was propietary and VERY slow, but it allowed assembly access to floating point math.
  3. While the basic on the 99 was very slow, I learned assembler on it, and the assembled programs were MUCH faster than the Vic-20 or C-64.

While it was less popular than other computers, it was a very nice machine for it's time. If TI had been a little more open with information and not so greedy....

Kerry High (khigh01@rollanet.org) writes:

The BASIC interpeter was built in to the console. The MINI-MEMORY cartrige added 4K of battery backed-up RAM, which could be used for Assmbley language programs or used to store one file called MINIMEM. MINI=MEMORY came with the Line-by-Line Assembler and a demonstration called "lines". The TI was 16 bit internally, 8 bit externally, sort of like the 8088.

Bill Leary (leary@emc.com) writes:

The processor was actually 16 bits, at a time when the competition was all eight bits. It's problem was that it had NO on-chip registers. Just a program counter, a frame pointer, and one other (status maybe). What on any other processor would been it's register set (accumulators, pointers, stack pointer, and so forth) was in RAM and addressed by that frame pointer.

Thus, it was indeed very slow, since what on any other CPU would have been a register-to-register operation, or a register-to-memory operation all became memory-to-memory operations.

The advantage was that you could get a whole new set of fresh registers in the blink of an eye by changing that frame pointer. And the OLD frame pointer even appeared in the new register set in a dedicated register. You basically could end up with a linked list of register sets. Pretty neat idea, but had serious performance limitations.

The microprocessor itself was based on the TI 990 mini-computer processor board. In the mini-computer the register file approach of putting all the CPU registers in memory made a lot more sense. The difference between RAM access and register access wasn't quite as dramatic as when the microprocessor came out.

Jonathan Leslie (jpleslie@delphi.com) writes:

The 4A uses a TMS9900 16-bit cpu on a 16-bit bus. Anything connected directly to this bus ran quite fast for its time. However, it was really slowed down by the fact that any BASIC program was doubly interpreted. First it was interpreted from the BASIC language. Then it had to be interpreted again because the 4A used TI's proprietary GPL (Graphics Programming Language). This unfortunately made the 4A quite slow when it needn't have been. Any programs written in Assembler though really zipped along.

The BASIC interpreter was built-in to the console so you didn't need any extras to program in BASIC. It was a limited BASIC though so TI released their Extended BASIC which came in a cartridge. This was a vast improvement over console BASIC. There was no RAM in the cartridge though to allow saving of programs. You had to do that either with the cassette (accurately portrayed in the article) or on disks in the external PEB or Peripheral Expansion Box. This box was big, yes, but no bigger than a modern clone box (fullsize). One thing TI did right, and that was they built all their hardware to last. Some of the toughest equipment I've seen.

The 4A's graphics were also superior to most computers of its time in that it had the capability of sprites and they could be programmed to be motion automated. You didn't have to keep messing with them. You could program up to 32 sprites at one time, with 4 occupying a screen line at one time before others of a lower priority disappeared when they passed that line.

The name of the computer came from: 99 (the 9900 cpu) - 4A (their model designation just like PS/1 or PS/2 or Pentium). First their was a 99/4 which had some very poor attributes like a chiclet keyboard and no sprite graphics. They updated the graphics chip from a TMS9918 to a TMS9918A, which had the much better graphics and hence the name 4A. It also had a sound chip capable of simultaneously producing 3 tones and 1 noise. That was eclipsed only by the SID chip in the Commodore 64.

There are still many people in the US and overseas using their 4A and many user groups. There are also at least 3 TI shows annually in the US and at least 1 overseas in Europe.

The current software abounds with programs that TI never dreamed possible when they manufactured the 4A. There are also hardware upgrades like MFM and SCSI hard drives, battery backed ramdisks (on plug-in cards) of up to 4 megs, RGB analog video and more. There is also a computer upgrade that will use the other 4A peripherals and run 99% of all 4A software. This computer on a card plugs into the PEB and uses a standard XT keyboard and has ports for analog video with resolution of up to 512x424x256 and a mouse.

Software includes WYSIWYG page layout programs, graphical art programs, GIF picture viewers, word processors capable of editing documents of up to 400k in size, and a new communications program that will communicate using 28.8k modems and display all IBM type ANSI graphics.

Many TI'ers and non-TI'ers alike still remark how the educational software written for the 4A and produced in cartridge form is still better than much of the educational software written for PC's.

Alan Ricotta (saturn@naples.net) writes:

The Texas Instruments TI99/4A was a 16 bit computer with 16 bit Internal CPU 16bit Memory Path

Strange 60pin CPU Chip. Largest CPU in a Microcomputer I've seen

16K RAM, UNK ROM, Has a special GROM (Graphics Rom) for Displaying certain Characters. Total Memory MAXED out is 72KB (RAM+ROM) with Addons. The Color Palette includes a Transparent Colour, For Layering Effects.

This unit was actually a revision of the TI99/4 (Note No A) The 99/4 didn't have a fuction Key. From My Information, the 99 came out in limited areas in 1980, I have found Copyright Dates on Older Carts going back to 1979.