Hello, welcome back to the 8-Bit Guy. So, Over the years, I've received numerous
emails from people who found a "computer" at a thrift store or a garage sale , or maybe
they just saw on a TV show or movie . And so they’re emailing me so they can ask me
what I can tell them about it. And so I reply to them that “oh, that’s
not actually a computer, it’s a terminal.” And the reply that most commonly follows after
that is, “what’s the difference?” And, while I'm sure most of my audience actually
knows what a terminal is, I thought I would just go ahead and make this video to explain
it to the rest of the world that does not. In the early days of computers, believe it
or not, they didn't have screens as we'd think of it. In fact, the really early computers only had
a series of switches and indicator lights. But as computers became more sophisticated,
they needed ways for the computer to communicate back to us humans in something a little easier
to read. You may have seen teletypes being used in
movies depicting rooms full of women typing messages back and forth with distant places. For example, these are from the movie Valkyrie. These were essentially the next evolution
of the telegraph. Instead of tapping out messages in morse code,
you could type on a machine that works very much like a typewriter, only your message
could appear on another such machine on the other side of the country. So, these machines were not invented specifically
to use with computers, but were rather adapted to work with computers as it was a natural
synergy of these two products. For decades, people used teletypes to type
commands to a computer, and the computer would return the output by printing to paper. These teletype machines could be in the same
room with the computer, or in another part of the building, or could even use a modem
to connect to the computer off-site. Some computers were single user systems that
would have a single teletype, where as larger computers could be multi-user and thus have
multiple teletypes connected. What's interesting is if you watch the original
Star Trek from 1966, at no point will you ever see computer text displayed on a screen. And what is more telling is that when the
enterprise computer speaks, you can hear the distinct sound of a teletype in the background. You can't really blame the writers, because
that was simply the paradigm by which people understood computers at that time. In fact, I’ve looked at a bunch of movies
from the 1950s and 1960s and I haven’t found a single one that depicts a computer displaying
digital text on a screen. Except for maybe 2001 space odyssey, which
does sort of depict that kind of thing. Ironically, science fact may have been a little
bit ahead of science fiction because Nasa did in fact have computer screens in mission
control during the late 1960s with the Apollo program. So, you have to really stop and consider how
advanced this sort of thing was for the time. But back to teletypes, there were a few downsides
to printing everything to paper, though. One obvious problem is that you go through
a lot of ink and paper, which can get messy and expensive. Another problem is that these machines are
pretty noisy, especially if you have a room full of them. And since they are mechanical, they probably
require regular maintenance. And so, at some point, somebody must have
had the bright idea to say “Hey, you know, instead of printing all of this stuff out
on paper, maybe we could just display it on something like a television screen.” A few years ago, I travelled to the birthplace
of the glass teletype, which was invented by Datapoint corportation in San Antonio,
Texas. The product was known as the Datapoint 3300,
which began development around 1967 and first started shipping to customers in 1969. The idea would be that it would receive serial
data and print the characters to a screen, usually at the bottom. And then as more data comes in, the information
would scroll up the screen and eventually disappear. So there would be no permanent record of what
was printed like a teletype. But that wasn't always a requirement. The important distinction here is that these
are not computers, nor are they computer monitors. terminals do not display a video signal, as
such. Instead, they are receiving one text caracter
at a time, transmitted as ASCII code over a serial data connection, exactly like a teletype
was designed to work. In order to learn more about terminals, I
decided to take a little road trip for this episode. So, I'm taking a little drive out to, kind
of the middle of nowhere to visit another YouTuber. His name is David Lovett and he runs the youtube
channel Usagi Electric. He's got some stuff that I think will fit
in very well with what we're talking about. If you aren't familiar with David Lovett,
he recently guest starred in an episode of Veritasium showing off some vacuum tube computers. He also lives in Texas, but lives in a rural
area called Hico. I had to drive seemingly forever through the
middle of nowhere.
I drove past this land full of grazing dinosaurs just north of Glenrose, TX. I kid you not. When I finally turned into his driveway, I
wasn't quite sure I was in the right place. I mean, there were wild deer walking around,
then I drove by some cows. The driveway just went on and on. But finally, I arrived at an actual house. And I hope you like the smurfy wrap I did
on my car and wheels. Anyway, here's David Lovette. he took me out
to his workshop. I'm sort of jealous of how much space he has
in here. Puts my little workshop to shame. he has some
little Japanese cars out here. I especially liked the little Honda Beat. It's a Japanese Kei car. it has a tiny engine, so it's probably not
very fast. This thing's like driving a go-cart. But it is so cool. I'd drive this around. Oh my gosh, but it is hard to get out of! So onto business. One thing I noticed right away is that he
had some old teletypes here. This one is from 1924, we think. And this one is going to be probably late
20s, maybe early 30s. 1929, 1930, something like that. So, this one's almost a hundred years old. But that was how to send data electrically. What it is missing is ticker tape. I don't know where you find 1 character wide
ticker tape. Also I need a new ribbon for it. So, this one doesn't receive at the moment. But it will send. The send mechanism is down here. So, if we plug it in, we can type and send
data out. Since it is a teletype, it's all 5-bit baudot. This one is also 5-bit baudot, eventually
we'll get the model 14 and the model 15 on the same current loop, and they will talk
to each other. So, if I push the letter G here, it will type
the letter G here. Push the letter F here, it will type the letter
F here. That's the hope, at least. I was also very impressed with this large
vacuum tube computer from the 1950s called the Bendix computer. And while transisters weren't available yet,
thus the need for vacuum tubes, germanium diodes were available, which did help to shrink
the size of this thing down to what it is. This is a rotating drum, so there's 8K of
memory in there. And then all of the logic. I mean, this is pretty much the heart of the
computer right here, the back side. Each one of these vertical slots you see,
one of those cards plugs into. Those cards are really simple, they just have
a flip flop, or a buffer, or an inverter on them, just building blocks. And then you connect the building blocks together
with this wiring to create complex logic. David has an ADM-3A terminal. This is a very iconic terminal that came out
in the late 1970s. Although apparently they are still in use
by the Time Variance Authority in the Marvel TV series Loki. Unfortunately, David's specimin is suffering
from something called cataracts, where a protective film on the CRT starts to form bubbles. Now, if you take a look inside the terminal,
what you will find is a bunch of TTL logic chips. There's no microprocessor in this thing. One side note is, when I was talking with
David Lovette, one of the questions I posed to him, since he knows a lot about this kind
of stuff, is you know, if somebody had thought about the idea of a terminal like using a
screen instead of teletype, back in like the 1950s, could it have been built out of vacuum
tubes? And the answer we both came up with after
discussing the technology for a while is yes, it absolutely could have been done with vacuum
tubes. Probably the most challenging part of it would
have been dealing with the ROM that would hold the character set information and the
RAM to hold the screen buffer. I mean, both of those things could have been
done but they were, that would have been probably the most costly part of it. Oh, and I’m sure it would have been pretty
big! David showed me another one of this prized
possesions, the Centurion. It's a mini-computer designed in the 1970s. It's a multi-user computer designed to handle
up to 32 terminals connected at once. While the terminal itself is branded as Centurion,
it is actually just a rebranded ADDS Regent 100, as I'm sure you can see the similarity. So, one thing that is immediately obvious
looking at this terminal is that it isn't quite as dumb as some terminals. While these terminals were often called "dumb
terminals" because they didn't have a CPU and couldn't execute code, some terminals
were smarter than others. The orignial terminals could only print text
at the bottom and have the text scroll up the screen, exactly the way a teletype was
intended to work. However, later terminals introduced certain
byte sequences that could instruct the terminal to clear the screen, or reposition the cursor. This allows for much more interactive programs
that can move text around on the screen. So, when I try to explain to people what a
dumb terminal is, a lot of people will come to the conclusion that it is essentially the
same thing as putting a keyboard and monitor in the same case, and calling it a terminal. This is a very crude, and somewhat inaccurate
explanation. First of all, not all terminals have the keyboard
built in. For example, this Digital VT320 that David
had in his shop, uses an external keyboard. The keyboard, however, is not connected to
the computer, rather to the terminal. But another interesting distinction is this. Pretty much any computer that uses a monitor,
whether that monitor is a television, a CRT, or even a flat screen, there is a universal
truth. That is, if you unplug the monitor from the
computer, the monitor goes blank. However, let's perform that same experiment
with a terminal. So that's all of the junk on our hard drive. And then. This is the data cable coming from the computer. So,if I unhook that data cable, you can see
all of the data is still there. Because the dumb terminal has its own internal
memory that stores whatever is stored on the screen. I can type, but it doesn't go anywhere. So, the terminal right now is completely unplugged
from the computer. So, if I type on the keyboard, you can see
nothing shows up here. And that's because the terminal is trying
to send ASCII data to the computer. So every time I hit a button, it's trying
to send 8 bits of data out to the computer, and the computer has to echo that back to
the terminal so I can see it displayed down here. Because the connection between the two has
been severed, nothing gets sent, and nothing gets sent back to the terminal as an echo. But all of our data is still sitting within
the terminal's own memory. If you think about it, this is the same behavior
from a teletype, because the text printed to paper would still be on the paper, even
if the teletype were unplugged from the computer. But if I lean on the back here, and I plug
it right back in, we can pick up right where we left off. Another DIR. It's like nothing ever happened. Most terminals were used in environments where
there was a large central computer, such as a mainframe or minicomputer. You can see them in people's offices in the
movie WarGames, for example. But some types of personal computers, even
those made into the 1970s and early 1980s were also designed to use a single dumb terminal. Most machines that used CP/M were designed
around a terminal for a display. In fact, back to our movie WarGames again
for a moment, you'll see the computer used by David is a CP/M based computer and what
he's typing on and looking at, is actually a dumb terminal. Some personal computers actually essentially
integrated a dumb terminal internally. This was quite common with computers like
the Osborne and Kaypro, because it was neccessary to maintain compaibility with the operating
system and how it expected to work. Another interesting example is the Apple 1. It has a relatively primitive dumb terminal
built right into it. And you can actually more or less divide the
board into the bottom half, which is the computer, and the top half which is the terminal. The downside to any computer using a terminal
as a display is that the vast majority of terminals were limited to monochrome text
only. And most of the early terminals couldn't even
reposition the cursor or clear the screen. As you might imagine, there weren't a lot
of games written to use these, as they were primarily meant for business use. However, there were some terminals that could
display color text, and even some that could display color graphics. These were pretty rare, and were still meant
primarily for business use, as they'd be far to slow to be able to update the screen quickly
for games. I did use my fair share of terminals however. This photo here is me around the age of 19
working at Mouser Electronics, and that's my terminal there next to me. But even before then, I used terminals on
my Commodore computers. But in this case, it's not a dumb terminal,
rather a "terminal emulator." Which is basically a piece of software designed
to make your computer behave like a terminal, and we used these programs to call bulletin
board systems of the time. And still to this day, on Windows, Mac, and
Linux, you'll find a program called terminal. And it is so named because it essentially
does the function of what a dumb terminal used to do, which is give you a window into
your operating system. As such, the terminal lives on as a virtual
thing these days. And that's it for this episode. As always, thanks for watching!
