For all the personal technology introduced and popularized in 2020 — upscale fitness bikes, at-home Covid tests, game consoles new and old — the personal computer lands on the list with a bit of a thud. PCs lack the novelty of other gadgets, but they’re practical, essential even, in a year when work, school and social life have come to rely heavily upon them.

While modern, ever more efficient computers are selling better than they have in years, vintage computers — impractical old devices in need of repairs and out-of-production parts — are also in demand on sites like eBay. Collectors also flock to message boards, subreddits and Discord servers to buy, sell and trade parts.

People are buying these PCs not necessarily for daily use, but for the satisfaction they get from rebuilding them. It’s a trend one might chalk up to quarantine boredom, though it’s been gaining traction for years.

Retrocomputing, the hobby is called, is hardly just a way to pass the time. Instead, as enthusiasts see it, it’s a means of communing with the past.

“You get into this mind-set of what it must’ve been like to be somebody in the late ’70s, having spent thousands of dollars on this thing that barely does anything more than a calculator,” said Clint Basinger, 34, who runs the YouTube channel Lazy Game Reviews. (The devices do allow retrocomputers to make art and music using software unavailable on new computers and to play 8-bit games, but not much else beyond that.)

“It’s like a time machine to me,” Mr. Basinger added.

Before the pandemic, there were several vintage computing conventions located around the United States, to which collectors brought their computers to show off. Attendees bought and traded hardware at these events, as well as meet the friends they’ve made online.

Huxley Dunsany, 38, said about 100 people used to pass through the Local, a cafe in Alameda, Calif., on the last Wednesday of every month for the vintage computing meet-ups he hosted.

“People were coming by walking by the cafe and doing big cartoon double takes when they saw all these old computers sitting in the window and coming in to ask what was going on,” he said.

But for now, there’s the internet. Sites like the Vintage Computer Forum and 68kMLA have helped people bond over the hobby since the early aughts. One of the largest vintage computing subreddits, Retro Battlestations, has more than doubled in size over the last few years, from 23,000 subscribers in 2018 to more than 58,000 as of this month. There are also active Discord servers devoted to retrocomputing, as well as old-school bulletin-board systems for people to use with their out-of-date machines.

Mr. Dunsany is passionate about bringing new people into the fold, especially those who lack a technical background or don’t fit the computer-nerd stereotype. “I would love to see more women in the hobby and more minorities getting involved because I’m a generic white guy in his late 30s,” he said. “I am sort of the default for this hobby, and I don’t want that to be true in 10 years.”

Madeeha Al-Hussayni, a 37-year-old photographer from the United Kingdom, got into computers after watching her brothers use the family device growing up; in her teens, she started making music on her Amiga. These days, she posts YouTube videos about retrocomputing as MsMadLemon. She said there aren’t a lot of women in retrocomputing communities.

“I was actually a little bit apprehensive getting into it, because it’s just me in a place where there’s everyone’s male and it sort of was a little bit, ‘How am I going to be received?’” she said. “I’ve had people who are supportive and happy that I’m part of it. There’s new people who have really been unhappy that I’m part of it. You know, half and half.”

Cost can also intimidate. For computers that are contained systems like the Amiga, released in 1985, collectors can pay anywhere from $300 to $650 for a working device. Other PCs have separate parts, and scavenging for pieces can get expensive quickly.

“It’s snowballed really, even in the last five years,” Mr. Basinger said. “I think some things are like 10 times as much as they were in 2015.”

If a collector chooses to buy all of the parts online, putting together a working Intel Pentium III 1133 from 1995 would cost about $500. A mid ’90s monitor alone can range from $135 to more than $2,000 on eBay, and that’s before shipping. The older the computer, the harder it is to find working parts and peripherals, so computers and parts from the late ’70s and ’80s can also cost hundreds of dollars online.

The most sought-after devices go for much steeper prices. An Apple-1, the tech behemoth’s Steve Wozniak creation, sold for nearly half a million dollars at auction back in 2019.

Amir Husain, the 43-year-old founder of the A.I. company SparkCognition, owns 150 vintage computers. He values both the technology’s connection with the past and its rarity when seeking items for his collection.

“I bought a Silicon Graphics Indigo at auction, which was used by Steven Spielberg when he created ‘Jurassic Park,’” he said. “On the front cover it says ‘The Steven Spielberg edition, 1 of 1,’ and on the inside, there are two business cards from S.G.I. executives with personal notes to Steven Spielberg.”

Ryan Horan, 22, has just three reasonably priced vintage computers in his collection: two Atari STs and one Commodore 64. He sees retrocomputing as a glimpse into a world he has never experienced.

“I was born at the tail end of the ’90s,” Mr. Horan said. “I just heard stories of things from my grandparents back in the ’50s and my parents back in the ’80s. So I’ve never been able to experience what those things were apart from stories and having physical things that were from that time that are still perfectly functional.”

Consider this next time you think about tossing a supposedly obsolete iPhone.