As we all know, Data has a photographic memory and can consume vast amounts of information. Assuming his capacity to retain knowledge is finite at some point, does Data purge some unneeded information after the usefulness is no longer relevant?

For example, his ridiculously long access code to lock all command functions on the Enterprise so he can see dear ol' dad was no longer needed after he unlocked the access code, nor would he need that specific code again. Or the contents of The Royale novel to find clues on how to escape the casino they were trapped in. After making his mission report, he might delete the contents of the book from his brain and retain the title of the book as kind of an indexing feature to lead him to reread the book later if he wanted. Or the number of steps he took on a particular day 7 years ago. You get the point.

Edit: I'm defining "unlearning" as deleting/purging/discarding of data purposefully or automatically by pre-programmed housekeeping protocols. This is different than forgetting (in the context of my question), meaning the unintentional I-forgot-to-feed-Spot or what's-your name-again types of memory lapses.

Also, "remembering every fact" doesn't necessarily preclude him from deleting some facts from his memory. It appears from what I've gleaned from the discussion so far is that some things Data can purge from his memory, while other things can't be removed. Is that the consensus here?

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    I'm pretty sure he has a really large hard drive, and doesn't need to erase things. He appears to archive lots of things, which require several seconds for him to access afterward. "Accessing..." Commented May 2, 2016 at 14:34
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    He once had a case of total amnesia. In the episode "Thine Own Self", he forgot his own name and past due to a blow to the head caused by a shuttle crash. This wasn't a permanent loss, as he was repaired at the end of the episode, but it's the most significant case of memory loss that I can think of. Commented May 2, 2016 at 18:34
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    Data has said many times that his brain is primarily built around a neural network. This is not entirely unlike our own brains. "Files" and discrete storage objects don't really apply in such a model, although he might have a way of linking out to additional snapshots or secondary offline storage. The size of the network isn't directly connected to how much data you push into it. It is a real technology but be prepared for very heavy reading.
    – user36551
    Commented May 2, 2016 at 19:06
  • Data's memory is indeed limited, by his own admission: Did Data have enough memory or "hard drive space"?
    – user15742
    Commented May 4, 2016 at 10:07

6 Answers 6


TL; DR - Data can forget things when deletion is justified

This started as a summary, but got a bit long! Anyway, below I present evidence that Data can forget things through hardware manipulation, but this doesn't seem to be in the spirit of the question which implies Data forgetting something through software means. If we interpret the question in this sense, we can say that it depends. I propose Data has a garbage collector algorithm that can delete certain redundant pieces of information. 'In Theory' proposes that he can 'consciously' use this algorithm, indicating he may indeed be able to forget something if he wished to. However, Data is unlikely to do this, unless the information is a resources-hog. It would seem that normally this algorithm would work 'subconsciously'. So, unless there is a need to delete something that one of his subroutines demands (perhaps his ethical subroutine or garbage collector), he won't forget it,

In 'Encounter at Farpoint Pt II', he says

DATA: I remember every fact I am exposed to, sir.

So, basically this suggests no, he doesn't forget.

However, it would seem rather careless of me Dr Soong to ignore this function. We know that Data has a limit to his storage capacity ('The Measure of a Man'). As pointed out in the question, does the number of steps Data took 7 years ago really matter? I think it's reasonable to think that Data has a complex algorithm equivalent to what we would call a garbage collector. If he didn't, he'd fill up his storage fairly quickly with fairly useless information; I doubt Dr Soong would want him to suffer a memory overflow!

It seems to me that he'd just fill up his memory as he goes, deleting information deemed as irrelevant by the garbage collector as more of a maintenance thing than anything else. As much memory as he have, because it is finite, it is still a precious resource which should be used appropriately, not being filled up with information that is now unlikely to be useful.

The other major example as pointed out in the comments below is when Data deletes his 'relationship' program designed in 'In Theory'. He points out in the episode that it is taking up plenty of resources and, by the end of the episode, he deletes it. Now, it could indeed be argued that this is a case of purposefully forgetting something and I would agree with that, under the proviso that this was a part of the garbage-collecting algorithm.

Regarding @Plutor's point about what happened in Insurrection, this does offer a method of Data forgetting. However, Data 'forgets' because some of his memory engrams (hardware) were missing. So, although this is equivalent to forgetting, it's like taking a small piece of your brain out to forget! From this, we can conclude that, strictly speaking, Data could forget something if he wanted to through removing hardware, although this seems somewhat extreme.

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    I can recall one significant instance when Data forgot something: Insurrection. Not only were his data engrams damaged by a Son'a weapon, but they were later removed by Geordi, and a lot of the second act was Data trying to discover what he had forgotten.
    – Plutor
    Commented May 2, 2016 at 13:36
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    I recall an episode where he had a relationship with one of the crewmembers who always went after unemotional men, and at the end of the episode they broke up. Data asked if he could delete the program about how to act in their relationship and she said yes. That sounds to me like a deliberate act of unlearning something that he had learned, in this case, forgetting how to behave in a relationship with her. Commented May 2, 2016 at 14:45
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    @N_Soong: I don't see the leap to 'he can't forget'. It entirely possible that he can erase memory, but the gaps in his memory would cause all kinds for mysteries to arise, leading to the same situation again. That's pretty much the premise of the episode, except not applied to Data's memory itself. Commented May 2, 2016 at 15:00
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    @T-1000'sSon Yes, in Eye of the Beholder Data mentions that he had at one point in his life considered shutting down and starting over. Ostensibly that would have caused him to forget everything he had learned up to that point, but seems a little more heavy handed than selectively forgetting the last time he used turbo-lift three to get to deck four, etc.
    – Xantec
    Commented May 2, 2016 at 22:02
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    @Thunderforge this gets philosophical though; is deleting a program (essentially a skill) the same as forgetting a fact? I think there is a distinction between those cases Commented May 3, 2016 at 0:30

I doubt he would need to

He certainly seems to memorize everything. From S03E03:

Doctor Beverly Crusher: Could I have your names, please, just for the record?

Rishon Uxbridge: I'm Rishon Uxbridge, and this is my husband Kevin.

Lt. Commander Data: Botanists. Originally from the aquatic city New Martim Vaz in Earth's Atlantic Ocean. Residents of the Rana IV colony for five years. You, madam, are 82 years of age and a composer of Tao-classical music. You, sir, are 85 years of age and a specialist in symbiotic plant life. You have been married for 53 years. I memorized the colony register on the way to Rana IV, in the event that such information would be needed.

According to this answer, Data has a memory capacity of 800 quadrillion bits, or 100 PB, giving him the capability to store thousands of years of video-quality memories if he so chooses.

Supposes he stores his memories as a Youtube 4K video, say at a bitrate of 70 Mbps. Then in a single year, he would use about 275 million megabytes, or 275,000 GB, or 275 TB. He could live for over 300 years on this storage. Now, keep in mind:

  • Storing life as a 4K video is not even remotely necessary to have an eidetic memory.
  • Data could potentially be upgraded (once Federation science caught up with Soong's genius).
  • Data has not existed1 for nearly 300 years as of TNG.

It seems likely that Data would never need to unlearn anything over the course of the show. Indeed, it is quite possible that increases in storage space would more than keep pace with the growth of his memories, since his memories grow linearly with time, whereas storage space may grow faster.

1. In Time's Arrow, Data's disembodied head endured several centuries, but presumably was not powered on.

  • Interesting answer, although I'm not sure about point 2 "Data can apparently be readily upgraded" - do you have a source for this? Even the leading scientists during TNG don't fully understand him. Do you have an example of when he was upgraded by someone other than Soong? Commented May 2, 2016 at 6:11
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    "Data has not existed for nearly 300 years as of TNG." Well, that's true for much of the series, but not after Time's Arrow, though I'm assuming he has no memories from that time. Commented May 2, 2016 at 6:56
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    Translating a picture of a letter to text might or might not be considered "unlearning" depending on the circumstances. For the text contents themselves, it's basically a form of lossless compression. But other information (relevant or not) is present on the letter - the colour and structure of the paper, crumpling, the exact way each individual letter is written, the spacing between words and lines... in some cases, this may prove to be important information. Most of the time, you can afford to throw away the 4k+ shot of the image in question and convert it to a tiny bit of text data, but...
    – Luaan
    Commented May 2, 2016 at 11:38
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    we know data has an upgrade socket in his mouth - intended for the emotion chip - and so does Lore. (TNG: Brothers S4 E3). So there is at the very least one expansion port of some quantity. Further, in several episodes, we see an ODN connection interface in use; any data in/out device is at least theoretically capable of being used to connect to a mass storage device.
    – aramis
    Commented May 2, 2016 at 13:12
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    Yeah, but how much does his OS, bloatwear and Facebook/Tumblr/Twitter cache (bad apps, bad) take up?
    – iMerchant
    Commented May 2, 2016 at 16:34

Let us not forget the time Data was infected with the Iconian Probe virus. He purged the virus by doing an emergency shutdown and wipe of affected transient memory, after which he did not recall what happened during the time of infection. [although, as only transient memory was affected, is this 'unlearning'?]

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    Yes it is unlearning, as cramming for an exam is also (short-term) learning. Commented May 3, 2016 at 9:31
  • @CeesTimmerman Cramming doesn't usually (ever) work.
    – wizzwizz4
    Commented May 3, 2016 at 17:39
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    @wizzwizz4 Then i guess i paid enough attention before doing it. Commented May 3, 2016 at 18:16

We're all simply accepting Dr. Soong's marketing is true about Data, that he never forgets anything. Just because Data says "I remember every fact I am exposed to, sir." doesn't mean he actually does. His various tricks with voice acting and long strings of data (like his verbal access codes) are impressive to us mere mortals, but for even modern computers they're not very impressive.

Data likely has a tiered storage system. (https://en.wikipedia.org/wiki/Hierarchical_storage_management) He obviously has a short term memory which he can purge data out of at will. The relationship program he deletes was most likely in the transient storage layer.

He'd have working memory, short term memory, and long term archives. (I always imagine when he tilts his head and says something like "working" or "searching" he's unpacking an archive). Remember, it's not just raw data size, it's the compressibility of that data we should be thinking about. Most days are the same, most facts are similar, and Data can use file de-duplication and file compression to archive long term memories in a way we simply can't as wet computers. This would allow him to "never forget any fact" while not necessarily "remembering everything." Some things just don't need to be remembered because it's exactly the same as something else.

Finally, Soong worked really hard to make his androids as much like humans as possible. Lore even had emotions. For Data, Dr. Soong intentionally dampened his emotional ability (although I'd dare say he's got some emotional undercurrent, even if he acts unemotional) to avoid the types of problems Lore caused. However, if we assume that Dr. Soong's success was because he tried to model humanoids, he likely also modeled Data's memory system on ours. It's likely he has a ton of storage, but like us, long term memory is more about reconstructing the memory from scattered remembered impressions. Data can supplement those with actual logs of actual spoken words, for example.

And it's possible that Data isn't even aware that he's actually forgetting plenty of things and only reconstructing memories or whatnot. Does C3PO actually use over 6 million forms of communication, or is that just his marketing introduction? How many times has C3PO told us that he knows 6M forms of communication... but that one is one he doesn't know, or he thinks it MIGHT be something else, or it's similar to one he knows. Isn't it possible C3PO just knows the nuts and bolts of communication and protocol and knows a few thousand of the most important languages, and handwaves the rest? Is he lying, or just telling us what Cybot Galactica's marketing department programmed him to do? Data's not lying, he's just saying that Soong told him about his memory.

Finally, we've seen at what speed and ability Data is able to access the Enterprise's computer to bring up mission data. I find it a bit unbelievable that Data hasn't thoroughly researched every mission in his quarters before his shift. He's got plenty of time available, and the show makes it clear that his work is his life. He's been seen working the night shift, etc. So why does he have to access the Ops computer so often to give Picard information about the mission? Supposition: he knows WHERE the data is in the computer, but didn't bother retaining it in his personal memory because it's accessible when necessary.

TL;DR: Just like Spock depending on everyone "knowing" that Vulcans Do Not Lie (despite them often lying in Enterprise, and "not completely telling the truth" in other properties) and Do Not Have Emotions (despite Vulcans showing off many emotions, and having more or less success at repressing them), I'd say that Data's "I don't forget anything" is nothing but marketing.

It's totally believable to us bags of mostly water that a walking, talking computer would have no emotions and have instantaneous, total recall. His various parlor tricks of voice acting and such would impress upon us his massive memory capabilities.

But just like Vulcans who can lie and have emotions, Data can forget details and shuffle memories into highly packed, somewhat lossy storage (like a JPEG vs a PNG). When he needs them, he can unpack them, reconstruct details with heuristics, and supplement his memory with the computer, all while maintaining that he never forgets anything.

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    That's actually a good example that counters some points on other answers here.
    – Ellesedil
    Commented May 2, 2016 at 19:25
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    For an entire galaxy, 6 million languages is really not that much; there are roughly 6,500 spoken languages on Earth today. And Data meant "fact" as his audience understood, not every theoretical fact such as the exact temperature of every inch of his seat (unless deemed important enough). Also where is the proof for your claims such as "never forgets anything."? Commented May 3, 2016 at 9:46
  • Spoken like a true cynic. +1.
    – Rand al'Thor
    Commented May 5, 2016 at 0:37
  • I appreciate the argumentation against the androids' alleged perfection, but I think it fails to see a point that has nothing to do with the actual universe the story takes place in. All the instances of "please wait while I do [X]" were most likely inserted to portray the working of Data's mind to the viewer of the show. Or even as opportunities for Brent Spiner to act out the sparse details that make the character Data seem vivid. I wouldn't take them all that literally ;)
    – Sir Jane
    Commented Apr 5, 2018 at 11:16

It is known from "In Theory" that Data is able to willfully delete subroutines that are no longer used, although I would not go so far as to call this "forgetting" as it is a matter of manipulating software, not data.

The episode "Clues", on the other hand side, makes very clear that Data does not (cannot) forget, in a sense of erasing data.

Picard orders Data not to reveal anything he knows about the first contact with (or the existence of) the Paxans after the second erasure of crew memories and for the entire duration of his existence.
If Data was indeed able to forget / delete data, it would make more sense to instruct him to erase the memories of said incident once the second deception had been successful.

(I seem to remember another situation where Picard says to a third party that Data can be trusted never to reveal some particular thing if ordered not to... although I cannot recall what it was. Same situation, if he could forget, he could more easily and more safely be ordered to forget than not to reveal.)

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    +1 for the point about "Clues." I think that's a clear canonical case to the contrary for forgetting memories.
    – Aaron R.
    Commented May 3, 2016 at 17:56

So long as Data has quantum-entanglement access to the multiverse there is no logical reason to anticipate permanent memory loss. I defer to those with personal experience in this field for subjective commentary on recovery issues. As soon as the problem of Borg-absorption is addressed to my satisfaction, I hereby apply for the upgrade from current wetware.

  • 4
    Huh? Can I have what you're having?
    – iMerchant
    Commented May 3, 2016 at 19:25
  • Lol. If Star Trek were real, you'd fit right in with the DS9 augments. Commented May 4, 2016 at 0:07

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