In Dune, how do people cope with the lack of computers?

From the glossary in the original Dune, about the Butlerian Jihad:

Its chief commandment remains in the O.C. Bible as "Thou shalt not make a machine in the likeness of a human mind."

Now, there is a huge difference between a simple micro controller or a pocket calculator and "a machine in the likeness of a human mind". Daily life presumably works fine with quite a few advancements made in electronics (see laser guns, personal shields, ...).

One would think that cloud computing, self driving cars and video game AI took a bit of a hit though. Especially since in that world it seems reasonable to err on the side of caution in those things.

In the prequels, not written by Frank Herbert, computers as we know them exist but AI is illegal.

However I think this was a bit of a retcon. In the original series, it seemed more like all programmable digital computers were heresy, but analog electronics were allowed.

So you certainly could have air conditioning, which people in real life have been using since the 1930s, and it could have a simple mechanical thermostat controlling it instead of a microcontroller, or even just a switch that you (or your servants) turn on when you feel hot and turn off when you don't.

As an example of a borderline device from the books: a suspicious Ixian recording device, Leto II's dictatel. It is possible to make a recording device with only analogue electronics, so this dictatel may have been permissible. However its small size and clever design seemed suspicious (in the real world, there are no analogue voice recognition systems, and although an analogue neural net for voice recognition is at least theoretically possible that also seems wildly against the spirit of the Butlerian prohibition). The Ixians may have cheated and used a computer, and who would be able to tell? Nobody outside IX had seen one in centuries.

Many things we do with computers these days can be done perfectly well without computers (and prior to the microcontroller explosion of the 90s, usually were). For example, the air conditioner you mention could be controlled just fine with a bimetallic switch to sense and react to temperature changes. This extends clear up to large-scale industrial systems: the Manhattan Project managed to build atom bombs without the use of a single computer.

Back in the 1960s, when Dune was first published, people would have been quite familiar with these systems, so Frank Herbert wouldn't have seen any need to call them out -- they'd just be part of the general understanding of the readership. Even so, they're mentioned from time to time in the books. For example, in Dune, there's a brief mention of a clockwork-based watering system for plants.

There are effectively two classes of computers: microcontrollers with a single or few limited and fixed functions, like your air conditioner; and programmable computers.

The Butlerian prohibitions would be mostly irrelevant to the former, while the latter would likely be forbidden. The smartphone in your pocket is a programmable computer. Is it anywhere near sentient? No. Could it be made to appear sentient? Yes, with some trickery. Which likely means it would be a no-no for the Butlerians.

That's a problem, because humans today are pretty dependent on programmable computers, even if we don't realise it. It's essentially a given that humans who have the technology to design and build faster-than-light starships are going to need ordinary computers far more powerful than what we have access to today.

The Dune universe simply handwaves this consideration, and indeed many others around technology, away with psychics and prescience and breeding programs. None of which are particularly credible as a replacement for sufficiently advanced computers.

Effectively, Dune is not a science-fiction novel, it's a high-fantasy one. Which makes perfect sense given the time at which it was originally envisaged (1965): well before computers became as integrated into our daily lives as they are today.

As an example, Herbert didn't believe that something as complicated as a faster-than-light transit between two stars could be calculated by ordinary humans, but he either didn't have the foresight to extrapolate how powerful computers would become (or feared that possibility, hence the Butlerian Jihad), so he invented Guild Navigator prescience to cover for this.

In short, Dune's world-building - especially in the areas of technology - is woefully inadequate. But that's mostly okay, as it's a story about people, not technology.

So the ultimate answer to "how do Dune's humans cope with the lack of computers?" is "they don't, because their society would literally be unable to exist, but it's not important enough to the overall story to lose any sleep over".

Remember that Dune was first published in 1965. There were no microcontrollers. No common technology incorporated computers. Few, even in advanced societies, had ever seen one with their own eyes. Some big organizations had them for accounting and payroll. Other applications were more exotic: R&D, missile guidance, ...

It was quite easy in 1965 to imagine a society without computers. My personal computing device in those days was a slide rule. However, Asimov had written about robots, von Neumann had written a book on the analogies between the computer and the brain, some researchers were working on AI, and other science fiction writers were interested in its possible dangers. So, at the time Herbert wrote Dune, it made sense to imagine a world that had rejected AI, along with most computers.

Now Mentats make perfect sense for doing political and other projections for the great houses but it would be impossible for a Mentat to replace the everyday control systems.

The little microcontroller in the air conditioners for example is a computer by definition, and if such microcontrollers don't exist then how does society function as a whole?

Computers on their own don't do anything (other than heat up the room); they're only useful when running a program (e.g. a control system, or whatever).

If we have a computer running some program, it can always be replaced by a dedicated circuit for performing the same calculations, known as an ASIC (Application-Specific Integrated Circuit). ASICs can be vastly more efficient than computers (that's why they're used for bitcoin mining).

The main reason we use computers is they can be reprogrammed: existing machines can be used for new tasks, and updates/fixes can be made to the program without having to build a new physical machine/circuit/whatever.

There's also nothing particularly special about electronic circuits, other than their speed. Both computers and application-specific machines can be built using clockwork, billiard balls, etc.

Hence the main effect of forbidding general-purpose computers would be slowing down innovation: they wouldn't have the quick feedback cycles we enjoy when hacking on software; they'd need to disassemble and rearrange their wiring/gears/etc. every time; and new products can't be 'downloaded', they'd need to either be physically shipped, or built on-site from blueprints.

This also incentivises simplicity (which is good if we also want to avoid "borderline" thinking machines), and solving problems using clever tricks/hacks if possible. This seems to fit well with the Dune universe: lots of their technology is simple, ingenious, and pretty much unchanged for thousands of years (e.g. shigawire, stillsuits/tents, all the various uses of suspensors like shields and glowglobes, etc.).

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There is a slight complication, since some programs are designed to run other programs (e.g. a Web browser can run Javascript programs). These are called "virtual machines". If we try implementing such programs directly, we'll just end up with a (slightly different form of) computer.

However, the above argument applies to these virtual machines too: they are useless without a ("higher-level") program to run, and such programs can be implemented by a dedicated (physical) machine. For example, we can build a circuit which implements the Javascript of a particular Web page, without having a general-purpose Javascript computer, or a general-purpose PC.