It's a rusty old computer that takes over a minute to perform a simple operation. A beaten-up computer that restarts unexpectedly and at the last time you would like it to.
This is The Alleged Computer. This computer, to put it kindly, isn't the most viable to use to lollygag or search. In fact, you could probably benefit using an old mobile phone with internet capabilities over this type of "computer". Their best use is probably a novelty doorstop.
If it runs overly slowly or breaks with a single touch (or only works properly with a very strong touch), it definitely fits here. If a computer is actually much more efficient than it looks, see What a Piece of Junk.
Compare The Alleged Car and The Alleged Steed for severely underperforming automobiles and horses. Also see No Backwards Compatibility In The Future and Our Graphics Will Suck in the Future.
Walking Techbanes turn any computer around them into this trope.
Newton Pulsifer, in Neil Gaiman and Terry Pratchett's Good Omens, has a singular knack for machinery. That is to say, he can make it stop working just by trying to make it work. And he always buys the worst. His computer is somehow always an early model with the hopelessly flawed chipset, or failing that, the early hideously bug-filled OS. And don't ask about his car.
The Quark II computer produced by the original WayForward Technologies in Douglas Adams' Dirk Gently's Holistic Detective Agency, which Richard MacDuff advises police (who have a non-functioning model) would be best used as a giant paperweight. (At which point the policeman he's talking to admits they're already using it as a doorstop.) The same book also contains a very much defective example of the not-exactly-a-computer-in the-conventional-sense Electric Monk, which does all your believing for you.
The first entry in the Jedi Academy Trilogy, Jedi Search, had Han Solo and Kyp Durron steal a ship that turned out to have a very old, very slow nav computer, which was a liability in a tense battle situation. As a result, they needed to brave the Maw, a dangerous black hole cluster, in order to evade pursuit. Thankfully this became a Suicidal Gotcha thanks to the Force being with Kyp.
Holly from Red Dwarf. Despite allegedly having an IQ of 6000, he (she in some of the later series) has gone very senile, and often blunderingly damages the people on the ship.
He tells us about his IQ at the beginning of the series and follows it up with "the same IQ as 6000 P.E. teachers". Considering his tone, he probably tried to explain right there that his IQ doesn't really mean a whole lot. It only sounds impressive to the other dunderheads on the ship.
In the Thunderbirds episode "Sun Probe", engineer "Brains" accidentally takes his experimental robot instead of a computer along on a rescue. When he's forced to ask the robot to make the calculations, it takes the robot a full 20 seconds (accompanied by obligatory clicks and whirrs) to make the calculation when (in spite of the pseudo-scientific nonsense-calculation used) it could have been solved on a pocket calculator as quickly as you could press the keys.
Subverted in a Tales from the Darkside episode, "The Word Processor of the Gods". Writer Richard Hagstrom receives a homemade word processor from his nephew Jonathan. The machine struggles with mundane text processing, but when it's commanded to rewrite Richard's life, the results are astounding.
Vice Principal Crubbs' computer from Neds Declassified School Survival Guide was so prone to freezing and crashing that it would often launch him into profanity-laced rants about how much he hated it, likely with his hand on the intercom button. At the end of an episode, he smashed it with a hammer in order to get a new one directly after telling a student not to do so.
Any PC multiplayer game that requires all the participants to get matched up with each other ahead of time and then actually load into the game (think League of Legends) will cause accusations of this from faster loading players against the slowest. "Are you loading the game on a typewriter?" is a typical comment.
One collection of comments from LOL's Tribunal (read: in-game chat) had an angry Lulu player denounce another gamer: "JESUS! Please upgrade your wooden PC powered by hamsters on wheels!"
Strong Bad from Homestar Runner apparently loves computers like this and uses them by choice. He mocks his friend The Cheat for using a modern Apple that doesn't have a text-based interface, he thinks a flat screen means someone cut half of the monitor away, and he thinks the Apple mouse is a bar of soap.
His first computer, the Tandy, fits this trope after Strong Bad continues to use it after it explodes.
The Compy doesn't show any negative qualities other than general obsolescence for its time.
The Lappy is known for being too heavy to be portable and has a battery life of five minutes.
Averted with his current computer, the Compé, which was current when the toons that featured it were made.
In Leftover Soup Jamie had a "Linux clusterfuck" of three laptops that were supposed to act as one machine but in practice didn't work without all three active at once and was much less powerful than even one of them by itself. He apparently bought the mess for $50 and the original creator had died with no documentation. Professional computer geek Ellen tried for a full day and night to make it work with one laptop but eventually just scrapped them and bought him a new laptop.
General Protection Fault: The secret organization of the Brotherhood of the Twisted Pair seek a geek "like none other, whose skills are without equal. He (or she) will initiate a golden age of geekdom, and lead a revolution of ideas that will revolutionize the computerized world." One of the tests is averting this trope with out-of-date machinery.
Fooker passed by building a server out of computer equipment made in the late 1980s, when said components were at least a decade out of date.
Sharon passed by writing down what you'd have to do in order to pull off a similar feat, using 20-year-old equipment.
Yoshi passed by having the computer equipment a college kid could buy on a budget confiscated by the FBI, because of what he did with it.
In Homestesque, Tyler has an Unbelievably Shitty Laptop with a CRT screen.
The Comics Curmudgeon has a theory that the Archie comic strip is written by the "Archie Joke Generating Laugh Unit 3000" (the AJGLU-3000), a quasi-sentient but primitive, very large, computer that attempts to mimic human interaction for humor.
The school's aptitude tests are scored by a huge mainframe-like machine named "Emma", which takes some Percussive Maintenance to operate. It said Bart should be a cop and Lisa a homemaker.
When Lisa's dishonest exam result pushes the school's average into the boundaries of acceptability, the school is awarded some money which is spent on, among other things, an IT department consisting of a single desktop computer, which was visibly about 15 years out of date at the time of the episode.
Peggy Hill in King of the Hill uses a Kaypro II (first released 1982) up until the turn of the millennium, at which point Hank buys her a 'blueberry' iMac.
The Bastard Operator from Hell keeps one antiquated machine around because his unfinished game of Dungeon is on it. Its hard disk failed a long time ago; the machine has been running from memory for untold years. Other stories also make fun of various outdated equipment, like one where he made a few bucks by selling users the right to chuck their crappy old hardware from the roof of the building. It's all good fun until an old mainframe lands on the boss' car...
The Apple III is an early example, being (as Steve Wozniak described it) designed more by committee than by actual engineers. A poor cooling system and other design flaws led to reliability problems due to overheating, the real-time clock could fail with prolonged use, and poor software support meant that many users had to rely on the Apple II backwards-compatibility feature to run Apple II software. Unfortunately, this feature only worked in 40-line mode, ruining the III's advantage of built-in 80-line support when upgrading a II with an 80-line expansion card would have been much cheaper. Despite the design flaws being ironed out in later machines, it still ended up being a flop.
Most of the Apple III's flaws resulted not from the engineering mistakes (except the early overheating power supplies), but from conscious corporate decisions that no one bothered to check by something as plebeian as common sense. Steve Jobs, for example, had a lifelong burning hatred towards cooling fans, and while he usually acquiesced to the engineering pressure, that time he had a brain fart and insisted that the computer not have one (nor any vents either). Limited Apple ][ compatibility was also dictated by the company's marketing department, who was afraid that it would be seen as a Video Game platform rather than the business machine they positioned it as.
Another early example was the Sinclair ZX80, which in addition to an (allegedly) barely usable keyboard had the design flaw of not being able to display anything whilst a key was being pressed (making it unsuitable for anything like games), as well as the available display area shrinking the more memory was used. Like its younger and more famous brother the ZX81, which had some of these design flaws fixed, it also only had a measly 1K of RAM and monochrome display (even the Commodore VIC-20 had more than this). Nevertheless these trade-offs made it the first home computer in the UK available for under £100, ended up selling some 100,000 units and proving mass-market home computing was possible, leading to the phenomenally successful ZX81 and ZX Spectrum.
Computers from budget brands tend to become this, with probably the only hardware that didn't require the bare minimum to pass was the parts from Intel or AMD.
Any computer becomes this after sufficient time has passed because Technology Marches On. What was cool ten years ago is an antiquated piece of junk by today's standards.
"Netbooks" fall under this trope from the start. Originally marketed for word processing and checking email, netbooks can't even do either of those well because they are completely underpowered at the time they reach the market, because most producers couldn't resist the temptation of installing the latest version of Windows on machines clearly too puny for it just to cash a commission from Microsoft, and then shoveled in three craptons of various bloatware just from themselves. Fortunately, most have since seen the error of their ways and do a better job balancing hardware and software sides now.
For various reasons, all modern desktop OSes tend to accumulate all sorts of crud under their hoods just from prolonged use — including installation and removal software, drivers, application modules, half-healed virus attacks etc. — which eventually leads to the OS beginning to trip over itself, causing slowdowns, unexpected crashes, "floating bugs" and general crappy work. The time it takes varies between platforms (and let's leave it at that), configurations and user behavior, but in the end, after several years of continuous usage, any PC can slow to a crawl just from this. While a competent admin can usually clean the system enough to be usable again, reinstalling it from scratch is often much faster and easier.