There are numerous places in various Star Trek episodes where references are made to the fact that "downloads" are a destructive operation: you download something from one place, and unless you explicitly made a copy beforehand, what you downloaded is gone from its original storage location and instead appears in some other location. Hence was born the term "copy and download".

There are of course out-of-universe, plot reasons for things happening that way which are exploited from time to time. There is also the out-of-universe explanation of how large media companies feel about people downloading copyrighted works, and a possible out-of-universe explanation that at the time, people in general may not have been intimitely familiar with the implications of the term "download", so they added "copy" to help describe what happens to at least portions of their viewership.

But is there a plausible in-universe explanation for why downloads would be destructive by default, and a specific copying operation would have to be made beforehand so as to not delete the data from its original location?

As for specific examples, these are two that I can think of right now (I'm quite sure there are more):

  • VOY "Twisted" (S2E06), right near the end, stated by Torres: "Our entire database has been copied and downloaded into somebody else's system."
  • VOY "Message In A Bottle" (S4E14), a little more than five minutes into the episode, the EMH is "downloaded into the transceiver array" for transmission across an alien sensor network to the Prometheus when the latter is in the alpha quadrant, and some 20 minutes into the episode it's established that the EMH is not available in the sickbay and will return later.
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    Can you give a specific example? "Numerous places" doesn't really help
    – Valorum
    May 16, 2016 at 19:11
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    Without further evidence, I think it's safest to say "copied and downloaded" is just redundant, not necessarily indicative of anything.
    – Harris
    May 16, 2016 at 20:41
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    In the late 21st century, after 100 years of vicious fighting, the MPAA-RIAA was finally in complete legal control of every communications device. Copyright enforcement became a mandatory component of all network protocols at all levels. Older non-conforming programs and devices were confiscated and destroyed. It became impossible to transfer any kind of information without proof that you had the right to make a copy - unless you simultaneously performed an irreversible deletion of the original, in a manner verifiable by the enforcement mechanism. (1 of 2)
    – user18979
    May 16, 2016 at 23:44
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    The phrase "copy and download" became common as a defensive measure. A request to "download" something could be interpreted as authorizing a deletion which you did not actually intend. Such interpretation was not technically mandatory, but the triumphant copyright enforcers, working behind the scenes, encouraged it as a default, because copying was, to them, a sacred act, not to be done casually or accidentally. As is often the case in human language (and human-computer interfaces), the usage persisted long after the original reason for it disappeared. (2 of 2)
    – user18979
    May 16, 2016 at 23:44
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    In the end, the only actual answer, and the only one that even makes sense, is, "Because the writers have no idea how computers actually work." Which seems a bit hard to credit from the standpoint of 2016 when everyone with half a brain understands the basics of these things, but even in the late 90s, most television writers could not have given you a coherent account of how computer data storage works (as evidenced by, well, almost all television that deals with computers in any way from that era or earlier). Sadly, this is not a very satisfactory answer. Just the only true one. Aug 25, 2016 at 19:52

5 Answers 5


So the only answer that would fit RL and in Universe is:

Star Trek computers work totally diffrent from how computers work now.

Sadly the authors do not provide insight on how isolinear computer technology works in detail, so it is hard to understand how copying and storing data in the Star Trek universe actually works.

From a real world perspective it is complete nonsense as any data stored somewhere is never erased by copying it. You have to either turn off the power for volatile memory or even actively erase the data from non-volatile memory.

Thus the only conclusion can be that Star Trek computers work in a totally diffrent way than our current computers.

That might actually not be so far fetched since we are approaching the physical boundaries of what you can achieve by CMOS technology. Currently Intel is developing 10nm technology - silicon atoms are 0.11 nm wide. So the gate length approaches atom diameters. It is expected that if the gate length is about halved again, quantum tunneling will be a non-neglectable phenomenon.

So by the 24th century, computing technology might be something totally different from what it is today simply because our current progress is reaching its physical limits.

On the other hand, current verly large storage systems can handle and store data in the range of Peta to Exo-Bytes. A human body has about 10^28 atoms. If beaming means storing all that information within the computers of the transporters, it would need some incredible storage and processing power on a level much much smaller than an atom... otherwise it would at least as many atoms to "store" the human information in another form - in that case a prefect 1:1 clone.

Even if holograms would be a lot less complex due to algorithms etc., it would still mean a tremendous amount of calculation power and memory to render and store holograms of that detail that they are indistinguishable from actual human beings.

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    Coming back to this question much later, your answer also reminds me of the fact that e.g. core memory has "destructive read"; in other words, reading a bit actually clears that bit, and it needs to be re-set as a separate operation (implemented either in software or in the hardware itself). Maybe Star Trek computer memory works similarly somehow?
    – user
    Jan 19, 2017 at 15:33
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    @MichaelKjörling - to be fair, DRAM, which is the ram used in your device right now, is destructive read and actually degrades in a matter of milliseconds and needs constant refreshing by continuously updating logic circuits. But it's fast. Apr 19, 2018 at 16:24

Downloads are not in and of themselves dangerous or destructive. In the first episode that you asked about, "Twisted"

B'Elanna reports that 20 million gigaquads of information was uploaded to their computers, while their computer database was copied

nothing was deleted information was added.

In the case of the episode "Message in a Bottle" the Doctors program was transferred from the mobile emitter to the transceiver array for transmission to the alpha quadrant. The entire EMH Program had to be transferred in order for it to function either in the emitter or as a subspace message. Voyager's computer was not capable of holding the original program and making an additional copy because of the size of the EMH program, The Doctor's entire program used 50 million gigaquads. That's why the Doctor was not available in sick bay and Paris was trying to hold down the fort.

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    I don't understand your comment "Voyager's computer was not capable of holding the original program and making an additional copy because of it's size"--if Voyager's computer could hold one copy at least temporarily (and it must have to send it to the transceiver array to transmit), why couldn't it just download a copy from the mobile emitter without erasing the data from the mobile emitter itself? That wouldn't require Voyager's computer to ever hold more than one copy of the data.
    – Hypnosifl
    May 17, 2016 at 0:28
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    Could you address my question above about why you think saving a copy of the program on the mobile emitter would require Voyager's computer to hold two copies rather than just one? Your last edit just changed "it's size" to "the size of the EMH program", but I don't see how that would help answer the question (I already understood you were talking about the EMH program, that's what I was talking about too).
    – Hypnosifl
    May 17, 2016 at 1:44
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    @Hypnosifl: The EMH is always "cut and pasted" into the mobile emitter, it is never "copy and pasted" the reason being the program is too large to have 2 copies running at the same time and that the program requires a specific processing device, see the Wikipedia link above. The Doctor does say that he makes back-up copies of his operating files but it is implied that these copies would not work outside of the basic program itself. So you could not duplicate the Doctor or have multiple Doctors i.e. one in sick bay, one on the holodeck and one in the emitter all at the same time.
    – sfhq_sf
    May 17, 2016 at 2:16
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    I still don't follow--the Voyager computer and the mobile emitter computer are entirely independent, no? Why would a copy running on one affect the amount of memory available on the other?
    – Hypnosifl
    May 17, 2016 at 4:14
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    Agreed. If the mobile emitter and the subspace transceiver can both hold the entire program, then why not just replicate a new storage device of sufficient capacity, or even another mobile emitter, to hold another copy of the program for backup? Clearly the Prometheus' computer is large enough to run both its own EMH and Voyager's EMH at the same time. Or, if they are just two avatars running in one program, then Voyager's EMH is not so large that they can't copy just the essentials of his experience and personality without having to copy the base program as well. May 18, 2016 at 2:45

"Message in a bottle" is bad example for the question, because hologram is very specific type of data/program. This was noted in question here:

Why would Professor Moriarty "cease to exist" if he tried to exit the holodeck via the arch?

As for the destructiveness of the copy/download I think you read too much into things.

Every time I remember when the download is "destructive" involves holographic data - i.e DS9 "Our man Bashir". Also, at least in Starfleet, the drive is to log everything.

Data destruction clashes with imperative to gain knowledge, so I believe you're asking about something you imagined. Not trying to be condescending here, just stating facts as I see it, so sorry if I offended anyone - not my intention.


My guess would be that computers in the Star Trek universe are based on quantum-mechanical technology, and data is stored as a pattern of quantum states. It is well-known in the physics community that quantum states -cannot- be exactly replicated; this is known as the "No-Cloning Theorem". I would speculate that part of the process of reading stored data involves 'quantum teleportation' of the relevant data to a holding area where a destructible digital copy of the data is fabricated, after which the original data is 'teleported' back. The same process, applied between ships, would account for the phrase "copied and downloaded" (though I would phrase it as "downloaded and copied" myself).


This answer is pure conjecture:

Starfleet computers could have safeguards in which they will not give up a piece of data without destroying it in the process, to prevent files from being read or modified without the crew's knowledge.

This could be accomplished with encryption. When created, a file would be encrypted with key-pair encryption and the computer would immediately destroy the public key and keep the private key only until the file is read. Then it would destroy the private key and probably the data itself as the data was read.

Copying then would be a procedure where you read a file, save two new copies with new keys, and destroy the original. (Or save one new copy and transmit the other)

Opening a file then would read the file to active memory, destroying the original, and saving a copy under a new key.

You could probably even use this method along with user credentials to make it impossible to hide who last accessed a file.

That would explain why just downloading would be destructive.

  • "This could be accomplished with encryption." Well, that reminds me of this answer right here on Science Fiction & Fantasy. Note point 1: "There is encryption but it is always breakable. P=NP will let you crack everything but one-time pads but the Federation stubbornly continues to use NP-based ciphers."
    – user
    Jan 19, 2017 at 21:40

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