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2: terminals are a very rich domain, and few people know the great diversity of terminals that existed historically

3: the best definition of "terminal", which distinguishes them from displays+keyboards, at least in the context of historical terminals, is: A terminal is a computer peripheral that transmits and receives data from a host computer, the data being best understood as an instruction or command (both to the host machine and the terminal), and where there is typically some internal state maintained on the terminal which describes the current displayed content and interaction possibilities (but which may not include all the possible content that can be understood as "displayed")

the rest of this thread is going to be a discussion of terminals of different forms, likely many of them will be unfamiliar to you, or if they seem familiar, the details of what they could do and how and why will likely be unfamiliar. anyway, let's see some terminals

the archectypal terminal in many peoples minds, the thing that people think of when you mention terminals, is the Character-oriented terminal. the oldest form of these were just teletype machines, literally just typewriters that were electrically controlled and which could be used to communicate with a computer, which could type characters, and also receive typed characters. here's an ASR 33 teletype, which is a particular machine used for communicating with computers. because these were literally type writers, they are called hard copy terminals

the upgraded form of this is the glass teletype or video display unit, which enables far more possibilities. probably the most widely known character-oriented glass teletype is the VT100, which still forms the basis of many minimum viable terminal emulator programs today. character-oriented VDUs were effectively just video based versions of teletype terminals. instead of a paper print out, they stored a screen's worth of characters in internal memory

its worth pausing here and bracketting these two toots by observing the large gulf in time and cost and so forth between these machines. we're talking like decades between the first teletypes and the first VDUs. teletypes existed looooong before computers, even. and even when VDUs existed, teletype terminals were still commonplace, because VDUs were expensive as heck initially

the expense was not because of the CRTs or anything like that, it was because of *memory*. that is to say, *computer* memory, not just terminal memory. and also because of *computer speed*

what i mean by this is, well.. let's consider a situation where you just drive a TV from a computer. suppose its, i dunno, 1960. everyone's got a TV in 1960 so they're cheap, right?

but now, if you want to drive it from a computer, you need to invent some mechanism for outputting a video signal. how are you gonna do that? real-time digital synthesis in the computer? fat chance! you might be able to control an oscilloscope that way, and many demos existed, but not a TV, with its raster graphics. and while you're doing the oscilloscope control, what else do you have time for? depends on the complexity of the thing you're drawing. funny lines for art or simple games? maybe. but text? forget it. you have no time for other programs

if you use a teletype as your output, you can just send a command to print a single character, it does, and then the character is still there on the paper indefinitely even if the computer turns off. so your program and just proceed to the next thing it needs to do

but what if you still want to use a TV? i mean, teletype machines are loud and fiddly mechanical devices

maybe you think, why not replicate the teletype's page, by storing character data in the computers memory and then use some specially designed circuit to non-destructively read that memory very quickly and generate a video signal? some sort of "video unit"

well that's nice, but for a computer in 1960, you're gonna use a lot of memory. i mean, suppose its 6 bits per character optimistically, then a standard 80x24 terminal takes 11520 bits, which is not a HUGE amount of memory but not dirt cheap either

in the 1960s you could get core memory for about a dollar a bit, which meant your little video output would be over $10,000. just for the memory! why bother when you can just use a bog standard mass produced teletype?

plus, if you were doing this by video, you'd have to wire up locations for video signal transmission to the remote displays. whereas a teletype can just be connected to a phone line if you need it. or you do wireless transmission of video? but that's still a lot. now you need radio engineers involved. why bother.

EVENTUALLY memory chips started to be built in the late 60s and costs really dropped for memory, and the size of the chips were small enough that you could actually start building VDU terminals that could produce some semblance of a terminal like the VT100

BUT the first VDUs weren't character-oriented! they weren't just glass teletypes!

the first VDU terminals to be produced were actually what are called BLOCK-oriented terminals. a block-oriented terminal does not send and receive data one character-qua-command at a time, but rather in large blocks. and the data was not merely a pile of characters but a far richer thing

the data that was received was an entire menu or form (like an HTML form), sometimes with things like data format validation info, and data sent was either a menu item selections or form field information

technically there were some hard-copy block-oriented terminals as well but they're pretty rare, because of the complications of making them work, and they're not merely a teletype

an example of a block oriented terminal, which is from 1964 (not the earliest but a fun one regardless) is the IBM 2260. it stored a very small number of characters in a delay line memory, which was probably the cheapest option for the amount of memory needed at the time. another fun one, from 10 years later, is the hp vt2640

these terminals LOOK an awful lot like the sorts of things we normally think of as terminals, they LOOK like character-oriented terminals like the VT100, but they were controlled very differently, and you used them very differently. you'd basically send them a large blob of data describing the entire screen, with form fields and so on, including layout information, subdivisions of the screen into static data regions vs. form regions, etc etc.

then, the user would be able to navigate around the menu items and form fields and enter data, all of which was stored locally on the terminal. only when the user pressed a _send_ button was all of that information bundled up and shipped back to the host machine

there is, incidentally, another kind of text-oriented terminal that is "line-oriented", and all i could find about those is that they were, well.. line oriented. which i assume means that the data came across to it in blobs of one line at a time

i don't know if it sent data one line at a time as well. character-oriented terminals typically sent data for every keypress. modern terminal emulators are character oriented on send, but we typically use them with shells that simulate a line-oriented send

now, you may think this is the end of things for terminals but this is just the beginning

well actually you're right to say its the end sort of because character-oriented terminals were VERY popular and lasted a VERY long time, and also they sort of were the LAST thing that was developed

but its not the end of the thread, at least :p

the next kind of terminal that i'll discuss is a *vector* terminal. i mentioned before the idea of controlling a CRT like you control an oscilloscope, and some very folx realized that this is actually a REALLY good idea, because vector art is quite small in size, so you can get very far with a very small amount of memory

@spiritplumber no

@spiritplumber as mentioned in the subsequent toot, more things are terminals that what most people are familiar with

@beka_valentine oh, I was thinking like a Minitel terminal (occasional sight in northern italy, we'd blue box to france to use them)