So you are watching early episodes of a show that is set in the Present Day (or what was the present for when the show came out). In Real Life when these episodes were written, tech that we now took for granted was just coming out, and the show would reflect this, showing everything from CD-ROMS, the Internet, computers (albeit with command line prompt) cell phones, and what have you as the latest thing.
Fast forward years later in Real Life to now. The show storyline is still set at the same time as the early episodes, and in order to keep up with the real world, the writers will have the characters now playing with MP3 players, high-speed Internet, smartphones, and computers with advanced OSs.
But wait, that episode that came out fifteen years ago was set only a month or two ago in the series' story line. How is it that the characters were touting tape decks as the next big thing, but only a short time later, older members of the cast are reminiscing on their old Walkmans, and younger members have no idea what a cassette even is, even though they were the ones lugging them around back in the first few seasons?
Simple, Long Runner Tech Marches On.
The trope only counts for works in which the characters of the series don't obviously age, and/or it is shown the series is set around the same timeframe throughout.
Compare with Unintentional Period Piece, where the work doesn't last long enough for this to become an issue during the story's run.
Anime and Manga
- The animated version of Sazae-san recycles most of its scripts every few years, updating clothing styles and appliances as appropriate.
- Ah! My Goddess (the manga version). The TV series hangs a lampshade on this when Belldandy comments on Keiichi still keeping his old appliances from the '80s in mint condition.
- Detective Conan has a particularly hard time of this, due to suffering from an extreme case of Comic Book Time. The series ran for over a decade, but Word of God claims that only a few months passed in the story (there's a lot of trouble with that statement, including the number of holidays we've seen, and the changing of the seasons.) Either way, the widespread use of cellphones and the rise of personal computers occurred during the run of the series, and became adapted into the stories concurrently, which creates some interesting problems. An early episode had a lunchbox-sized portable fax-machine qualify as an awesome gadget, while a more recent episode had a writer's lack of familiarity with cellphones used as proof that he hadn't left his attic in years. And canonically, those two incidents were - at most - 3 months apart.
- This does occur to Kochikame. There are plenty of sci-fi tech in the series, but it does update consumer tech from home computers to cell phones.
- Wandering Son began in the early years of The Noughties, which was a fast paced decade for technology, thus this is inevitable for a Slice of Life. For example, early on few characters had cellphones but recently most characters do. There's also a case of Technology Marches On where in the manga, in a volume that came out in 2006, two characters record their voice using a tape recorder. Cut to the 2011 anime adaptation and the scene is changed to them using their cellphones instead. The series barely takes place within 6 years so far, so it seems a bit realistic compared to other examples.
- Lupin_III The First Three Parts were animated in the '70s. One episode showing Lupin playing Pong. Part Four was animated in 2014 and shows modern smartphones.
- Superman—Started out as a Great Depression-era comic. Now, they have the latest iMacs.
- Archie Comics. The characters don't age, but the technology is always up-to-date. It's not something that's just quietly slipped in either; a strip in the late 80s saw Veronica replacing her record collection with CD's, and in a more recent one Archie's parents reminisced about the days of dial-up.
- The Disney Mouse and Duck Comics. While aesthetically with many bygone elements, the level of technology is always assumed to be contemporary (not counting Gyro Gearloose and other inventors occasionally pushing it well beyond that), so that cell phones or desktop computers may crop up in more recent stories. A notable exception are the stories by Don Rosa (active from 1987 to 2005) which are always either set in the timeframe "late forties to early sixties" (the time in which Carl Barks created his classic stories), or are prequels taking place at very specific dates in history.
- Batman: At the start of his career, a radio small enough to fit in his belt buckle that could be used to send Morse code was bleeding edge. Nowadays he has his own satellite network. Modern stories set in Batman's past tend to fuzz technological details by avoiding showing specific tech. Fortunately a punch to the face has always been a punch to the face.
- The Marvel Universe is actually more prone to this than DC, which reboots its continuity every so often, particularly with those characters - Peter Parker, Tony Stark, Reed Richards - who work with fantastic technology, the earliest issues of which involve technology which often wasn't so fantastic 10 years ago or so, when the Fantastic Four took their ill-fated space flight to the Moon (to beat the Russians), and contemporary Marvel continuity began. A prime example? Reading the original Iron Man appearance, one might be amused to discover that the secret to his suit's power was "highly miniaturized transistors."
- In the early Cat Who... books Qwill has a clunky manual typewriter that he refuses to replace with an electric one. In the later ones he has a clunky electric typewriter that he refuses to replace with a word processor. It's still claimed to be the machine he used his entire journalistic career.
- Young Wizards: A computer obtained by one of the characters in the third book starts out as a typical 80s Macintosh-like device. By the seventh book, it has "evolved" into a modern-day laptop, despite less than five years passing in-universe.
- The gadgets in Alex Rider used to be disguised as Game Boys and early Harry Potter books. He's since moved on to iPods, without aging more than a year.
- The fairies in the Artemis Fowl universe are supposed to be high-tech, with technology significantly beyond anything humans have produced. And while some of their tech has remained in Sufficiently Advanced Technology territory, a lot of their technology has quietly become upgraded over the course of the series as real-life human technology has reached new heights, making some of the fairy tech seem backwards in comparison. While the series has progressed forward in time, it's worth noting that in-series, fairy tech has been high-caliber for a long time and is not generally noted as making significant improvements.
- Alan Dean Foster started the Humanx Commonwealth series in 1972; its older novels show Flinx looking up information on microfiche, whereas recent ones have him hacking a global computer network when he's only a few years older. Notable in that one of the novels, Bloodhype, was set chronologically near the end of the series, but written back in the 70s. Foster himself acknowledges that this makes for a jarring plunge in tech-level whenever you read them according to the in-universe timeline.
- The Helmsman Saga has been started in the 80-s. The latest installment was written in 2011, and features cellphones along with SMS messages.
- Stargate Atlantis, where (set in the present day) the expedition had a seemingly limitless supply of gadgets, which mysteriously kept updating with rather recognizable new models which hadn't even shipped yet at the show's premiere, in spite of being cut off from Earth until the Dædalus showed up.
- Hi and Lois: Look at the photo on The Other Wiki here, and compare the TV to the modern TV the family has now, not to mention the other conveniences that they have.
- Blondie's family has been around for decades, and (as noted on the main page) has stayed the same age since the 1940's. However, the family now owns a flat-panel LCD screen and keyboard, presumably attached to a computer of some sort.
- BattleTech. Somewhat averted here. First put together in 1984, and the universe grew and developed. A thousand years in the future, wars are fought over the knowledge contained in books, firing computers weighed huge tons, computer networks pretty much didn't exist, EPROMs were advanced technology, and highly explosive fusion power was a high level of technology. 26 years later, we've got the internet, the iPhone, electronic books, and...well, we're a lot closer to fusion power than we were before; it certainly won't be a wait for another few hundred years. The authors, though, have maintained continuity citing that it's the future of the 1980s, not the future of today.
- Over the course of the Nancy Drew adventure games, Nancy transitions from using land lines to basic cell phones to camera phones to smartphones, and from borrowing suspects' desktops to owning a laptop to downloading thorough her phone.
- Arthur: Early episodes had Muffy, the rich girl, the only one with a cell phone, and Arthur's family owned a computer that seemed to be command prompt and had a very primitive GUI. Later episodes had everyone else owning a phone, the computers up-to-date with 21st technology.
- The Simpsons: The technology in the early episodes definitely reflected that the show took place around the same time they were produced, the 90s. Bart used a typewriter to write a paper in an early episode, and the kids in the series played video games on what appeared to be a SNES/NES mashup. Later episodes reflected the 2000s/2010s period, though it took until the show's 2009 HD conversion for the family to have a flatscreen rather than the dials-and-rabbit-ears cabinet TV they had.
- South Park: In early seasons a DVD-player was a sign of rich status, that only one family in town could afford. Now, various characters can be seen buying DVDs, playing Xbox, and having a Facebook account. Yet the boys have only advanced one year in the school.
- Played straight and subverted on King of the Hill. Earlier seasons make use of cell phone, televisions, internet, video game consoles, and computer designs of the mid to late 1990s. Episodes throughout the 2000s show technology of the times when it comes to some vehicles, phones, televisions, and computers. Throughout the 2000s episodes Bobby still plays a Gameboy, they still have a standard definition TV, and Peggy uses a 90s model iMac from 2000 til the end of the series.
- One episode does revolve around them buying a very large HDTV with surround sound and being so unused to the clear picture and booming sound that they eventually take it back.
- The greater DCAU has something like this, since the original Batman: The Animated Series was deliberately made to evoke the character's 1930's noir roots, while Superman: The Animated Series and others are much more modern. As a result, Gotham City got a massive tech upgrade between seasons as BTAS was updated to match STAS.