Reverse engineering the Sega Channel game image file format

ndiddy | 245 points

This is not a dissimilar system to Teletext[1], which transmitted data in the blanking interval of a broadcast TV signal, and could be interpreted by a TV or other hardware with appropriate support. Teletext was pretty widespread throughout Europe in the 1980s and 1990s.

It was typically used to transmit pages of information (news, weather, etc.) that could be viewed directly on the TV, but the BBC's Ceefax[2] Teletext service was also used to distribute software to the BBC Micro, when equipped with the appropriate Teletext Adapter[3].

In a similar fashion to the Sega Channel system, the Teletext system would broadcast looped data, with popular pages (such as news and weather) being repeated frequently so they would load quickly, and less popular pages taking longer to load (or more accurately, to wait for the next time they appeared in the looped data).

I was interested to see that the Sega system used a bitrate of 8Mbps, which sounded pretty high for the mid-90s, but I see that Teletext had a bitrate of almost 7Mbps for PAL broadcasts, despite being roughly 15 years older!

[1] https://en.wikipedia.org/wiki/Teletext

[2] https://en.wikipedia.org/wiki/Ceefax

[3] https://en.wikipedia.org/wiki/BBC_Micro_expansion_unit#Telet...

abirkill | 18 days ago

I don't know how I convinced my parents to get me this in elementary but not a single other person I ever met had heard of it. I had no idea it had interesting tech, definitely didn't know it used satellites.

It was a really unreliable service, at least for me in Virginia. We had to call support all the time the short time I had it (1-3 months).

``` They would then send everything to a company called Foley Hi-Tech, who would create the game menu graphics/animations and insert all the monthly content. They ended up with a ~60MB file called a "game image", which was burnt to a CD and sent to a satellite uplink facility in Denver, Colorado. The CD would then be installed in the uplink game server computer, which would continuously transmit the game data in a loop over satellite. Cable headends all over the US would receive the satellite transmission and send it to cable subscribers. The data being sent in a continuous loop is how the service's "interactivity" was achieved at a time when cable TV providers could only transmit data to all subscribers and couldn't receive data (i.e. what game a given subscriber wants to download) ```

swozey | 18 days ago

I remember Sega Channel. In 6th grade, my friend had it. I didn't grow up with BBSes and had only learned about the Internet the year before (from the same friend), so the idea of downloading games was pretty wild. The service was way ahead of its time.

IIRC, it was $15/mo. There was a monthly or weekly rotation of games, including some pre-releases. I think at one point we played Vectorman when it was still new in stores or possibly just prior to its official launch.

trzy | 18 days ago

I've been following the Billy time games release of different sega channel stuff. I remember a friend having it through TWC when it was active and thought it was really cool.

I hope more information comes out about the system setup specifically (like how out of band signaling was used if at all) so the service might actually be able to be recreated ala the way dreampi has allowed webtv to be "reactivated"

thepolish | 7 days ago

Had this back in the 90s for a month or two. It was amazing. A bit finicky. Our neighbors split out cable outside and it stopped working. Apparently needed a dedicated line.

sandoze | 18 days ago

Apparently the hardware had 4MB of RAM in case anyone else was curious.

pram | 18 days ago

Curious if you could have recorded say, 5 minutes of the channel and they played it back when you wanted to load a game. Assuming new games every month, you could fit a years worth of games in a VHS?

ada1981 | 18 days ago

SNES also had a similar service called StellaView that was only available in Japan. They had live farro and timed legend of Zelda 1 completions iirc.

I used to play some of the roms of these games. The one of Legend of Zelda was pretty slick, redone with A Link to the Past graphics.

https://en.m.wikipedia.org/wiki/Satellaview_games_from_The_L...

carrja99 | 18 days ago

This seems to have a lot in common with how the Nabu computers worked, especially the continuous loop of programming to get around the fact that you couldn't upload data back to the cable company. Really cool!

Kehvarl | 18 days ago

Cool! My dad worked on Sega Channel at General Instrument but we never actually had access to it because ironically our home's cable provider was terrible and didn't offer it.

1auralynn | 18 days ago

I didn't even know this service existed. Broadcasting games in a loop seems pretty clever, but I suppose ZX Spectrum already had games delivered over radio years before then.

omoikane | 18 days ago

PKSPREAD related to PKZIP by Phil Katz somehow?

firesteelrain | 18 days ago

Had this as a kid, for the most part it was great! I remember Vectorman being one game that never seemed to work well.

karlgrz | 15 days ago

[flagged]

Fortim | 18 days ago