[HN Gopher] Reverse engineering the Sega Channel game image file...
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Reverse engineering the Sega Channel game image file format
Author : ndiddy
Score : 221 points
Date : 2024-12-08 00:10 UTC (22 hours ago)
(HTM) web link (www.infochunk.com)
(TXT) w3m dump (www.infochunk.com)
| firesteelrain wrote:
| PKSPREAD related to PKZIP by Phil Katz somehow?
| mook wrote:
| Given the text:
|
| > Thanks for choosing SA-Ware for your packet spreading
| requirements!
|
| It's probably short for "packet spreading"
| firesteelrain wrote:
| Ah makes sense. I missed that part!
| pram wrote:
| Apparently the hardware had 4MB of RAM in case anyone else was
| curious.
| MBCook wrote:
| Oh that's pretty big.
|
| Obviously full sized games couldn't fit in the built in 64k of
| normal RAM, so they had to be put somewhere.
|
| I only got to use Sega Channel once. I knew about it from
| reading magazines, but when we went to a family Thanksgiving
| gathering it turned out my cousins had it! I don't know if they
| were a test market or not, I don't remember what year it was so
| I don't know if it had been deployed nationally yet.
|
| I don't know if I realized how it worked. I think cable modems
| may have started to exist by that point so at the time I
| probably assumed it was actually two way communication.
|
| I would've killed to have it at home. Sega Channel is the first
| place I ever played Sonic 3-D Blast, the two have always been
| linked in my memory because of that.
| ndepoel wrote:
| 4 MB is the maximum size of the console's ROM address space, so
| this would've allowed for any Genesis game to be published
| through this service, with the exception of the few games that
| used bank switching to go beyond 4 MB (really only Super Street
| Fighter II). 4 MB was a lot of RAM to be putting into a
| relatively cheap consumer electronics device in 1994, so I
| imagine some of the cost of that was subsidized by Sega and had
| to be covered by the subscription fees.
| swozey wrote:
| 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) ```
| SllX wrote:
| > 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.
|
| It was an interesting almost niche thing. My cousins had a unit
| and the service which I played all the time, but trying to
| describe it to other children at school years after the fact
| was difficult because nobody had ever heard of it. Honestly it
| was a toss-up if they even knew what a Genesis was at that
| point in life. I didn't even know what a Sega Channel was
| called until I had finally found a solid description online
| with an accompanying picture at some point in high school.
| jbmny wrote:
| I vividly remember playing Genesis in my living room as a kid
| when my parents were having friends over from out of town. My
| dad and his friend came in after a couple beers and my dad
| explained what I was playing. His friend knew all about
| Genesis already: "We've got the Sega Channel. I play 50 games
| a year!" I remember being very fascinated until he started
| laughing, which to me signaled that he was pulling my leg. I
| spent the next 30 or so years thinking the "Sega Channel" was
| a dumb joke from an inebriated friend of my dad's. Until
| today.
|
| Looking back, maybe my dad nudged him to change the subject
| so that I wouldn't spend the next month begging for a
| subscription.
| nerdix wrote:
| I knew of no one that had Sega Channel and I only knew of its
| existence because I had a subscription to Sega Power around the
| time of its launch which was covered in the magazine.
|
| The article claims 250,000 subscribers at its peak but it might
| as well have been zero on my little world. It's interesting how
| a service could have a quarter million subscribers and you
| could have basically no proof that anyone used it at all. That
| would be unheard of today. If Sega Channel launched today.
| Those 250k subscribers would be posting on social media,
| creating dedicated subreddits, uploading review videos to
| YouTube and live streaming on twitch. Anyone with even a
| passing interest in it would encounter the content of its
| users. The internet has really made the world smaller.
| ndiddy wrote:
| Using satellites to transmit the game data wasn't TOO exotic, I
| imagine they did it because all the cable headends were already
| set up to receive national channels carried over satellite.
| Having centralized control of the game server also let them
| switch out the game images for timed events such as
| competitions. For regions outside the US, Sega went the simpler
| route of putting game servers at each headend and mailing out
| CDs each month.
|
| It makes sense that it was unreliable in certain areas, cable
| TV was analog back then so cable providers didn't really have
| to worry about signal noise being a serious problem until Sega
| Channel came along.
| omoikane wrote:
| 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.
| MBCook wrote:
| It's interesting as a technical hack more as the way they
| figured out to get it over cable before DOCIS and 2-way
| communication.
|
| Makes a lot of sense. A TV channel is just a stream of data, so
| just stream all the data you might need over and over and over.
| Kwpolska wrote:
| Is it really a hack? Teletext also worked like this, and this
| service does not need interactivity, so it doesn't need 2-way
| communication.
| Cthulhu_ wrote:
| At one point Teletext on some channels had a two way system
| of sorts - a chat service where people could send messages
| over SMS to a paid for service, which would then be
| broadcast over teletext.
| agent86 wrote:
| The system I'd love to have a better understanding of is
| the one TiVo deployed for the transmission of data to their
| boxes in the early 2000s.
|
| They would buy a 30 minute paid programming in the early
| hours on cable TV networks under the name "Teleworld Paid
| Programming". The box would tune the channel, record the
| show, and then decode the data from the recording.
|
| I always thought there was something interesting there, as
| the process would need to survive the MPEG encode/decode
| process on the TiVo itself in addition to whatever they
| needed to do the broadcast.
|
| https://www.youtube.com/watch?v=VfUgT2YoPzI
| epcoa wrote:
| > figured out ... DOCSIS and 2-way communication.
|
| It's not even so much 2 way communication in the local cable
| system as the fact that cable TV companies were not
| originally ISPs. Sega Channel was a broadcast over C band no-
| return-path satellite, it didn't have any Internet related
| moving parts.
| hed wrote:
| I don't think of it as a hack any more than Sirius or XM
| making a "control plane" signal by just interleaving the
| what's on or channel map in with the music signal.
| IntelMiner wrote:
| DOCSIS was unrelated, but was absolutely _helped_ by Sega
| Channel. Sending data down the wire required cleaning up the
| signal sent out from the cable plant (and into the sega
| channel unit) a _ton_ relative to analog cable at the time
| esaym wrote:
| I remember the TV commercial, but until now I had completely
| forgotten about it....
| ada1981 wrote:
| 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?
| ndiddy wrote:
| You wouldn't have been able to capture the signal with a VCR as
| it wouldn't have made it to your TV. You would have had to
| somehow record the modulated cable signal before it went into
| your cable box.
| fredoralive wrote:
| If it's anything like teletext, normal VHS wouldn't have the
| bandwidth, you might have some success with SVHS, although
| unlike teletext it might not be framed as a normal TV signal so
| the general tuner / recording circuitry might also have
| problems.
| jandrese wrote:
| Not on a regular VHS cassette because it is transmitting data
| even during the vertical blanking periods. If you had a way to
| capture the channel signal raw it might work, but that would
| have been some expensive hardware in 1995.
| sandoze wrote:
| 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.
| kotaKat wrote:
| A lot of cable plant maintenance got its hand 'forced' with the
| introduction of Sega Channel and other interactive services.
|
| Who woulda thunk that a little blue hedgehog paved the way for
| cable Internet? ;)
| abirkill wrote:
| 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...
| nanoxide wrote:
| Teletext is still very much alive in Germany, pretty much every
| channel offers it. In fact, I use it most days to quickly check
| if there are any interesting headlines to follow up online, or
| for sports results. It's funny that it is frequently faster and
| easier to navigate than most enshittified news websites.
| mcraiha wrote:
| Same in Finland. There is a one guy running the show
| nowadays. https://yle.fi/a/3-12131551 (article only in
| Finnish)
| Cthulhu_ wrote:
| Same in the Netherlands, but it's updated to the modern age
| with a website / emulator [0] and app [1], both appropriately
| styled.
|
| [0] https://nos.nl/teletekst
|
| [1] https://apps.apple.com/nl/app/nos-teletekst/id289246732
| tobwen wrote:
| It was even crazier in Germany! In 2000, the television
| station NBC received a radio license for RadioMP3. They
| broadcasted the charts and entire albums (with covers) via
| teletext, which could be legally recorded at home. Bit rate
| 128 kbit/s - simply with a TV capture card. The public
| broadcaster also transmitted software via "VideoDAT" during
| its ComputerClub program. However, this required special
| hardware.
| andrepd wrote:
| I have seen more than one old geezer in NS trains reading the
| news on the Teletext app on the smartphone :)
|
| Maybe they're into something?
| wgx wrote:
| Thank you for this! You just unlocked some old memories of
| "Digitiser" which led me here:
|
| https://teletextart.co.uk/artists/paul-rose-mr-biffo
| phire wrote:
| Teletext had an instantaneous bitrate of 6.9Mbit, but it was
| only active for a few lines per frame during vertical blanking.
|
| The continuous bandwidth of teletext was only 324 Kbit.
|
| The main innovation of Sega Channel (and similar approaches
| from about the same time) was allocating a whole TV channel
| exclusively to data.
| ndiddy wrote:
| You got me interested in how the signal was transmitted, so I
| looked a bit more into it (see https://segaretro.org/File:Seg
| aChannel_Applications_Scientif... ). It turns out that the
| 8Mbps number I eyeballed from looking at newspaper coverage
| of the service was incorrect. When the cable provider
| received the Sega Channel data stream, they'd split it into
| two 6Mbps carriers. This allowed them to transmit Sega
| Channel data without having to dedicate a channel to data, as
| they could put the carriers between cable channels or in the
| portion of the spectrum used for cable FM radio. I updated
| the webpage with the corrected figures.
| phire wrote:
| Yeah, I was wondering how TV-like this channel looked.
|
| It's tempting to wrap it in fake horizontal/vertical
| blanking so it still looks like a TV signal (and you can
| send it through existing equipment that's expecting a TV
| signal). Essentially just Teletext but using every single
| line.
|
| But what Scientific Atlanta created is much closer to cable
| internet. The total bandwidth number is notable, each 6Mbit
| carrier uses 3Mhz of bandwidth, so the two of them add up
| to 6Mhz, which is how much bandwidth a standard NTSC
| channel occupies.
|
| I suspect this is because they have rented a single TV
| channel worth of bandwidth on the Galaxy 7 satellite for
| disruption to local cable companies.
|
| Splitting into two 3Mhz carriers has the additional
| advantage of allowing the receiver design to be simpler, it
| only needs to tune into one at any time.
| epcoa wrote:
| > I was interested to see that the Sega system used a bitrate
| of 8Mbps, which sounded pretty high for the mid-90s,
|
| This was over cable TV, so not very difficult to obtain these
| rates compared to general broadcast TV. Cable internet service
| rolled out in this time period with downstream rates of 40 Mbps
| per 6 MHz channel.
| trzy wrote:
| 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.
| carrja99 wrote:
| 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...
| Kehvarl wrote:
| 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!
| 1auralynn wrote:
| 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.
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