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The TMS9918 video chip is the common thread between those machines, and it's a fascinating bit of hardware.

The interface between the TMS9918 and its host system is dead simple: 8 data bits, 1 mode bit, 1 chip select bit, and nothing else. It manages its own 16 kB of VRAM and no other timing or clock signals are required between the 9918 and its host CPU.

As a result it was used in all sorts of machines of the era: TI 99/4A, Colecovision, Coleco Adam, MSX, Sega SG-1000, plus multiple different expansion cards for the TRS-80 and Apple II. It also supports genlock video input and was used in early-80s video production.

Most importantly, its programming interface is well defined and extensible. It allowed Yamaha and Sega to produce upgraded chips for the Sega Master System and MSX2 while maintaining backward compatibility, something that Commodore wasn't able to do with the VIC-II chip in the C64.

In late 1981 I built a computer around the Z80, TMS9918A (actually 9928A as I wanted PAL-M output) and the TMS5220 voice synthesis chips. I called it "Einstein" and only found out decades later that there was a computer from Tatung with the same name, processor and video chip that sold in the UK in 1984. Great minds think alike, it seems...

I was not able to get a datasheet for the 9918 and had to abandon the project. In early 1983 I did get a nice book from Texas Instruments by asking them to send it to an address in the US, but I only skimmed it. That was a huge mistake. A few months later I started a new computer project for the Logo programming language and remembered that Logo in the TI99/4 kept "running out of ink". There were only 256 different characters which could be redefined but the screen was 32x24 = 768 characters in size. So 2/3 of the screen had to be blank as the turtle moved around it. So I went with the Motorola 6883/6847 combo instead (the same as the TRS-80 Color Computer).

It so happens that the TMS9918A used in the TI99/4A has a new mode that the TMS9918 didn't: you can divide the screen in 3 with a different character set for each part. That would have given me Logo with infinite ink.

The TMS9918 is as simple as it is beautiful. A couple of years ago I wrote an MSX emulator in Java for fun. A pretty accurate TMS9918 emulator took just a couple of hours to write with the original technical handbook at hand, in 561 lines of Java code.

https://github.com/tjitze/TMSX

I am making a Youtube video series about the TMS9918A. So far, I’ve driven it with an Arduino and a 6502. The next video will get VRAM hooked up.

https://www.youtube.com/playlist?list=PL3itg4Usn3F-24qjSrlY4...

I think the Z80 was overall, due to its instruction set, the 8-bit CPU of choice unless the system builder needed to be cheap; and this makes sense given it was pretty much engineered to be a cheaper CPU than the Motorola 6501.

So it made sense that Commodore used a 6502 variant and I'm betting Nintendo chose a 6502 core for its NES to keep costs down. But all your old Japanese 8-bit arcade games of the 80s were Z80-based.

The Famicom used a 6502 clone from Ricoh in part because that’s the only thing they could find; every other chip manufacturer had too much backlog. They had already used the Ricoh chip in arcade boards, and just went with that one.

While more computer and console systems were designed with a Z80, the 6502 computers and consoles vastly outsold the Z80 systems.

The Z80 has more powerful instructions but they take longer to execute. The 6502 instructions are faster but you need more of them to do the same task.

In the end, a 1 MHz 6502 was almost equivalent to a 3 MHz Z80. The Z80 was available up to 4 MHz but often ran at 3.58 MHz) and the 6502 was mostly 1 MHz (eg. Apple II, Commodore 64) but in a few systems (eg. BBC Micro, Commodore 128) it was 2 MHz.

My trusty graphing calculator, a TI-85, also was Z80-based.

Motorola made 68xx, MOS Technologies made the short-lived 6501 which became the famous $25.00 6502 with some tweaks.

I think some of this is just that the industry was really small at the time. If you wanted a processor there were only a handful of choices, and most were completely unsuitable (too expensive mostly) for the home market. Low cost graphics and sound were similarly small markets. But it was also a wide open field in the home console biz, especially with ATARI spectacularly imploding only a few years earlier, so lots of people were throwing their hat in the ring and building the kind of system that made the most sense given the available parts.

MSX was an industry standard of making home PCs so it's easy to port softwares.

And the MS stands for Microsoft.

MSX was the original Xbox.

AFAIK, MSX stands for "machines with software exchangeability".

I don't know what the letters stand for but this was definitely a Microsoft (and ASCII Corp.) project for standardization of home computer hardware. Like XBox, but multi-vendor.

This is correct and it's mostly in Eastern part of the world. I owned a Spectravideo 328 when I was a kid. One of many kind of MSX computers.

The 328 was the precursor to the MSX standard. The 728 was MSX.

The differences were so small you could load most MSX programs on the 328 if you used a small software loader.

I learned this about 25 years too late. :-D

That was an afterthought, so that japanese companies didn't think they were directly tied to Microsoft.