Yes, definitely.
Initially interacting with a computer meant physically moving components around, later programs would be fed directly into the computer by various means (paper tape and punch cards in the earlier eras, other means later) and executed directly.
But directly feeding programs into a computer usually meant giving them to a human intermediary, most people never got to actually be physically near the computer. A person would give their program to a tech who would then, later, give them the output.
The shortcomings of this approach were obvious from the beginning, and spurred the development of terminal interaction.
A terminal was a non-computer input/output device which was connected to the actual computer via cables. Early terminals were repurposed teletype machines and output to paper, which was so wasteful that terminals with screens were quickly developed.
What this has to do with networking is that it quickly became obvious that since people were interacting remotely with the computer, via cables, there was no particular reason why you couldn't use existing cables to connect a computer to a terminal. Like, for example, the telephone network.
From there it's an easy jump to connecting computers so they can exchange data across a network, whether a special purpose cable connecting two computers on the same campus, or using the phone network to connect computers across the country.
After all, if your interaction with a computer is through a terminal connected to the computer by a cable, what does it matter if the computer you're interacting with is down the hall or across the country?
Note, this is also the origin of operating systems. Back in the era of directly putting machine code on punch cards or paper tape or what have you into a computer and having it directly execute the code there was no such thing as an operating system. You kept track of your files yourself, and you (or the technician) put them into the computer.
But if you're interacting with the computer via a terminal, and other people are also using it, then the computer needs a meta-program to keep track of which programs are supposed to be executing, who has access to various files, etc. That meta-program is the operating system.
Computers were being networked experimentally as far back as the 1950's, and by the 1960's a variety of approaches to networking were in use connecting computers across several discrete networks.
Enter ARPA, the "Advanced Research Projects Agency", now called DARPA "Defense Advanced Research Projects Agency".
ARPA started funding research into large scale networking in 1966, and in 1969 the first ARPA sponsored network was started.
By 1973 two of the larger discrete networks were inter-networked with ARPANet though things were still officially experimental.
In 1975 ARPANet was declared officially operational. By 1977 it was networking computers across the nation, mostly owned by big universities, the military, or a few large corporations.
In fact, it's interesting that you ask about 1977 specifically, because in addition to Star Wars being released, we also have a surviving network map of the entire ARPANet from that year: http://imgur.com/gallery/fjbXB The gallery there compares it with an ARPANet map from 1973.
Notice how many of the nodes on those maps are clustered together? Those are existing networks, computers networked on the MIT campus for example, and that entire network was connected to other discrete networks. Those smaller discrete networks are intra-networking, networking within an organization. When they were linked that was inter-networking, connecting discrete intra-nets into a larger inter-net. Later we dropped the hypen and that's why we call our global computer network "the internet". Because it connects millions of intranets.
The technology used in ARPANet is the foundation of the modern internet, TCP/IP protocol which is foundational to all internet communication was developed for ARPANet, and ARPANet remained a sub-section of the internet until 1990 when it was officially closed down.
So yes, by 1977 the idea of the military having a computer network was not merely an idea, but something that had been implemented for several years and was not classified or otherwise kept secret. Computer networks in general was decades older and there were practical, working, examples of computer networking from as far back as the 1950's.
It isn't exactly academic history, but if you're interested in early computing and networking I'd recommend the book Hackers by Steven Levy. It focuses mainly on MIT's programming culture in the 1950's through the 1970's, but covers the development of networking and operating systems as they evolved.
The first part I'm going to answer is what were the largest computer networks know of at that time; ARPANET. This was a Cold War project that would allow for decentralised communication, data storage and "super computer" capabilities which was understood at the time to mean multiple computers running tasks in parallel as part of a single program. It was a large network of computers that crossed the United States, including Hawaii. Wikipedia has a great image showing the network's status in 1974. While the scale and scope of ARPANET was a secret, its theoretical underpinning was not. Public research papers like D.W. Davies' "Proposal for a Digital Communication Network" defined both the concepts and the language we'd use to discuss them. "Proposal for a Digital Communication Network" for example defined and labeled the "packet". And so even though people may not have know that such a large network really existed at their time, the knowledge that it could and exactly how it would work were public knowledge.
By late 1967 the basic ideas of what a computer network should be and what it should do were in place. It should support:
However, you might notice that this doesn't quite line up with how R2 uses the Imperial computers and is at odds with the whole premise of the movie's opening act. If we could transfer data over the network, why move the data by disk and risk it not getting there?
That's because much of the feel for computers in Star Wars comes from terminal + mainframe systems. These were large computers which were shared between a large number of different users. Users could access the mainframe either via a terminal which was hardwired or via a local phone line. Before networking, moving data between mainframes could only be done via tape.
One other part of your question I just want to touch on quickly is the idea of an "interconnected vast computer network". That implies multiple networks interconnected, as we have today. The basic networking stuff was worked out on a theoretical level in the 1950s and 1960s, and therefore can be assumed to have been knowledge available to the writers or technical consultants on Star Wars. However, "internetworking" (as it was called) was extremely cutting edge science at the time they were making Star Wars and while the first internetwork connection from the ARPANET was in 1972, I don't think it was common public knowledge. Therefore I'd imagine that the Imperial network was, in the minds of the writers, a single network instead of a network of networks. Of course it's also possible that the writers wouldn't have know about this distinction at all, but the historical point still stands that the development of networking and internetworking wasn't a single field until the late 1970s.
All told, the historical background for how computers work in Star Wars is one part computer networking as we think of it and one part terminal/mainframe systems. R2 himself is both a microcomputer (that is a computer small enough to move between rooms) and a terminal. The networking we see in Star Wars reflects some of the concepts we see in science journals from the time and therefore includes terminals, microcomputers, mainframe computers and computer networks but lacks explicit mention of more cutting edge ideas such as internetworking.
Sources:
[I'm so excited to be able to answer this question but this is my first answer here, ever. I know about the strict moderation rules of this sub and I hope that I'm doing an okay job with this response!]
In 1969, the US Department of Defense established ARPANET which built on existing technology for remote access of computers across a network. ARPANET expanded on this technology, introducing early forms of email and file transfer, and utilized TCP/IP protocols which are still in use today. By the early 1970s, TCP/IP had evolved such that multiple discrete networks could communicate with each other, creating more or less the first thing that resembled the modern Internet in terms of its conceptual design.
The vast majority of people who were actually using this technology in the beginning were government officials and computer science researchers, but by the mid-1970s, smaller, more localized packet switching networks were becoming common in corporate and commercial settings. Companies were using these networks, primarily, to transmit data for storage and processing (think: calculations, bookkeeping), and email. In this scenario, the network was facilitating communication among servers and terminals that may have been in different buildings or even different cities, but they were limited to the network that they were contracted with -- imagine if you bought Internet service from a regional ISP, but could only communicate with other computers on that network. Most communications would have been internal to a company or organization. This is the type of corporate network communication that an end user would have been familiar with if they used this tech at work in the 1970s. It was by no means vast, especially when we think about how we communicate over networks in 2021, but it was a big change from how computers had been used just a decade prior. (If you compare how computers are depicted in 1977's Star Wars to how they are depicted, for example, in the original Star Trek series in 1968, the idea of what a computer can do and how it can facilitate communication and information sharing is quite different. The computer on the Enterprise stores vast amounts of data and does many complicated processes related to the functioning of the ship, combat, etc. but it doesn't necessarily communicate in real time with the rest of Starfleet to regularly update that data, though concepts like this do appear in later Star Trek series frequently.)
What's interesting is that if you look at contemporary sources from the early 1970s, the concept of using a computer network as a general-purpose communication device was still somewhat new in practice. While we do data storage/lookup, file sharing, and real time communication (like email and chat) in the same breath nowadays, that was certainly not the case with ARPANET or any of the smaller commercial networks, and the idea of using a network like ARPANET for normal communications (like we use the Internet nowadays) was not widely accepted when the technology was emerging. It was sometimes considered gauche or outright inappropriate to use it for marketing purposes or casual, personal communication. But a large, government network like the Galactic Empire computer system was right in line with how the technology was being used by real governments and companies in the 1970s, just at a much greater scale than was practically possible at the time.
In short: the idea of accessing a vast computer network containing data from around a large Empire would likely have seemed futuristic but not unprecedented. Conceptually, it would have been a marriage of sorts between the smaller networks used for corporate purposes in the 1970s and something like ARPANET. Star Wars isn't considered hard sci-fi by any means, but its depiction of communications and network technology wasn't really a reach for the time period.
further info: - https://archive.org/details/ComputerNetworks_TheHeraldsOfResourceSharing 1972 documentary "Computer Networks: The Heralds of Research Sharing"
I want to break this down into two parts. In the first part, I want to talk a bit about the history of Science Fiction, particularly focusing on the era that likely influenced George Lucas (1950s-70s). Second, I will talk a bit about the history of computer systems/networks in the 1970s.
Science Fiction has always had some computing concepts well ahead of it's time, it is one of the cornerstones of the genre after all. The "Big Three" (Isaac Asimov, Arthur C. Clark, and Robert Hienlein) of the last half of the 20th Centruy each tackled issues in computing that were relevant in their time (and even today), but also tackled "classical" ideas in philosophy and fiction. Isaac Asimov introduced the idea of a super computer evolving into its on Network in his 1956 classic short story The Last Question. In the story, the computer, network, system, and terminals all belong and connect up to the same "computer"/AI. Arthur C. Clark addressed this slightly in his 1948 short story The Sentinel, but most people better know the story as he collaborated with Stanley Kubrick in the 1968 movie and novel 2001 in which a spacecraft has an A/I super computer "HAL" has terminal interfaces throughout the craft. In Robert Heinlein's The Moon is a Harsh Mistress, the Lunar Prison Colony's central computer "Mike" becomes self aware and along with the protagonists leads a lunar revolution. There are other computers on the Moon, but they do not have the higher functions as Mike does and he is able to use his lunar network access to hijack all sorts of systems from communications to lighting and habitat controls to banking.
The general theme here is some what established computer systems for stations, ships, or planets are all more or less one large interconnected computer with terminal interfaces for input/output. In some cases, those inputs and outputs could be other computers or electronic devices, but the prevailing thoughts in Science Fiction in that era is that computer system components might be getting smaller, but the systems themselves were rather large, centralized, and expensive. The revolution of small, stand alone networked computers wasn't exactly a mainstay of Science Fiction, mostly I think because the central computer could act as a "character" to explore while the "stand alone" computers might be thinking robots instead.
So in the Star Wars Universe there seems to be conveniently placed computer terminals that are networked to the main computer (or Imperial Network). For the most part the sort of terminal access that allows such access are located in secure/semi secure areas where in theory only approved Imperial droids would connect to the system. Again this seems to align with other works of Science Fiction from that era. So the concept of gaining access to a computer network/system by attaching to a terminal is certainly something that had been around in fiction for some time.
So now to jump out of Fiction and into a bit of Computer History. Computers have played a role in the Defense Industry from the very early days of computing/cryptography. By the 1960s large computers had branched out into business and various levels of government and played an important role in landing on the moon. Most of these systems were closed systems in that there was typically a large room sized computer or computers that lived in a special climate controlled room with nearby access terminals and perhaps some more remote input/output terminals that were wired directly back to the main computer. Pysical access to the building and room were the terminals were located generally meant that you had access to the information that the computer could display to those terminals. There would be certain classes of data or certain reprogramming of the system that would require physical access to the computer room itself. Military installations would take security of these computer rooms/systems very seriously with armed guards with security clearance checks along the way to get access to sensitive military secrets (like nuclear missle targeting computers). Banks would use the computers to help keep and calculate accounts. Businesses would run payroll and accounting on their systems. Universities would use them for research and teaching the next generation of computer scientists.
Again these were all stand alone systems and transferring of data from one computer to another that was not co-located in the same facility generally involved transferring of magnetic data tapes. There was some possibility of using the telephone service to connect two computers together over greater distances transfereing the data over a more or less audio connection, but again it required a direct connection from one point to another and not any sort of shared connection.
By the mid 1960's the department of defense had expresses some desire to upgrade the phone system in the country to prevent a nuclear attack or an act of sabatoge to leave an area or region of the country out of phone communication with the rest of the country. ARPANET came online in October of 1969 linking computers in Stanford and UCLA and by December a stable link between the University of Utah, UCSB (California Santa Barbara), Stanford, and UCLA was established. Network sites grew slowly between Universities through the 1970's. In the mid1970s the US department of Defense essentially cut off all funding that did not directly deal with military application. This caused some splitting and securing of the network and the people involved in creating it. Defense networks would become more separated from the network that became the forerunner to the internet and the researchers who were interested in the field outside of the military would need to look to companies or universities for direct, non-military funding. By 1977 the grandfather/father of the internet was running but, for the most part, it was an academic or military apparatus that connected those large computer rooms together, allowing some remote terminal access to various machine rooms around the country, but again the majority of accessibility required physical access to a room that was connected into the system itself.
Stand alone or Personal Computers were being created by the time of Star Wars release, but typical communication between these smaller, desk machines was via floppy disks (save icon to you younger folks). It was fairly rare and expensive to actually join one of these machines to the network/internet, but it was doable via a modem that would connect to the network via the public phone system. This actually meant that with the right sort of knowledge and the right sort of equipment you could access computers and systems using nothing more than your home phone for physical access!
How much of this knowledge was available to the average person attending a 1977 showing of Star Wars? I think that might be an important part of the question. Certainly a decent number of the audience would have at least heard about 2001: A Space Oddysey in either movie or book format and probably some number had seen Star Trek when it was on television. Certainly, a good number of folks would have some knowledge of computer systems from work or the bank enough to know that you had to have some sort of physical interaction with an input/output terminal to get information. I believe that the concept of using a robot to physically connect to a terminal to "hack" the system would seem fairly plausible to most of the audience members.
To answer posts below - ARPANET wasn't the earliest large network.
ARPANET happened because the US realised it needed a robust network, and it was also a convenient way to share information between universities and research centres.
But before ARPANET there was SAGE - the Semi-Automatic Ground Environment. This was a working - i.e. not primarily experimental - network of extremely large (i.e. football pitch sized) computers placed around the US to provide advance warning of an incoming bomber attack. It was linked to fighter formations and missiles to generate a semi-automated response to an attack.
The impressive thing about SAGE is that planning began in 1954 and the system was partially operational by 1958. This was at a time when computers were extremely exotic items, and the concept of a computer network spanning an entire country was completely novel. Much of the technology - landlines, modems, networking protocols - eventually (sometimes very eventually) evolved into the technology used for the modern Internet.
The less impressive thing about SAGE was that it was almost completely useless. Regular tests were carefully choreographed to give the impression that SAGE would produce exceptional outcomes. In reality the system not only had blind spots, it was far too slow to deal with a post-1950s Soviet bomber fleet. According to some estimates it might have intercepted 25% of an incoming fleet, leaving 75% to level US cities to rubble - without counting ballistic missiles, which were tracked by a different later Strategic Air Command system.
Even so, it remained in operation until the 80s. But it was essentially a giant pork project which handed public money to the fledgling computer industry in the US - most obviously MIT and IBM, but also Burroughs and a number of other smaller manufacturers.
This was an excellent investment economically, but perhaps not so useful militarily.
An oral history of SAGE [1] outlines the problems very succinctly.
So... by 1977 the US already had a giant computer network. In fact the C3 (Command Control Communications) concept had been around for a couple of decades, and ARPANET was very much a spin-off and improvement. [2]
What the US didn't have was a public network. But that was never part of the original ARPANET design.
(Nor is it something you'll find on an Imperial Star Destroyer.)
