My two cents:<p>If we are talking about 1970s and '80s machines, they tend to run pretty hot, related to the PSU technology. Things like electrolytic capacitors "don't like this" and may contribute to cascading failures. PSU failures are apt to fry some chips, some of which may be hard to come by. So, better keep them cool = off.<p>If you consider machines from the 2000s retro, continuous run, avoiding the stresses caused by system start, may help keeping them alive. (I've a MacPro running since 2008, with no failures, apart from failing 3rd party ECC DDR3 RAM. Some of this RAM has even failed twice, the RAM originally shipped by Apple is still fine, though. This machine has only been ever off, when I've been on vacation.) – Machines from the 1990s and early 2000s are pretty much the same, but typically suffer from poor capacitors and/or batteries. So…?
Especially with older disk drives if you don't power them up for a long time (months) the bearings may seize, at which point you may have to use the hair dryer trick to try getting them to work again.
I have a 42 year old apple //e that had been in an uninsulated attic in Boston for 30+ years. It booted fine and all the 5 1/4" floppies worked. I know that C64s need the caps replaced and the org external power supplies can catch fire. I'd be really surprised if 1990's pcs failed. There was a period of transition to non-lead solder where many pcbs from that era suffered shorts from whiskering but everything else should be fine. Electromigration tolerances in the 90's cpu families was even more strict than today.
I switch most of mine (70-80s) on a few times a year and of them I use a lot (weekend game dev); I have to replace capacitors quite often, but outside that they all work. Unlike more recent (2000+) pc stuff which is all dead. All Sun and SGI stuff still works well though.
if you never turn the computer on, why does it matter if it's hypothetically still functional? boot it occasionally, the only thing that keeps a machine alive is someone caring for it
I'm not an expert, but I'm convinced the answer is "off". The reason is "on" accelerates growth of whiskers.<p><a href="https://en.wikipedia.org/wiki/Whisker_%28metallurgy%29" rel="nofollow">https://en.wikipedia.org/wiki/Whisker_%28metallurgy%29</a>
No matter what you do it will all need servicing.<p>Capacitors are perishable. Electrolytics dry up, solid (MLCC, polymer, tantalum, paper) dont like humidity (some even require baking before soldering). Mechanical stress and temperature cycling leads to cracking of caps and solder joints.<p>Mechanical parts will have stiction (hdd heads), dried grease. Plastic parts expand due to moisture (sprockets/cogs in FDD/CD), rubber bands liquify or dry and stiffen.<p>Then you have vented helium/lost vacuum.
Early 1990s dec machines: 3100 m series and 4000- 60 90 90a 705<p>If you have a modern scsi2sd card solution as your drive, off is fine. Just make sure all fans can spin prior to boot.<p>If you have a classic SCSI or expansion box with a big SCSI, on.
Same situation if you have functioning dssi drives. Let them spin.<p>Don't have to read/write or full boot just get to Chevron prompts and do a show dev to get it all spinning.
What’s the point of a retro machine from ‘98? Any application from that era should run natively on a modern machine. It’s past the point of games locked to a certain MHz or special purpose video drivers. If you want a CRT, just get a CRT. What’s the appeal?
Old components are still (and will be) manufactured, since so many old tech depends on it, like refrigerators, air conditioners, washing machines, microwave ovens, ...