In March of 1971 Intel released the very first microprocessor onto the market, it was called
the 4004.
This along with 8008 processor released the following year helped to jumpstart the computer
revolution.
But does that mean there were no computers before the microprocessor?
Well we know that certainly wasn’t the case as computers such as the Digital PDP-8 had
seen widespread use in business since the 1960s.
In fact the guidance computers used in the Apollo spacecraft were also designed in the
1960s.
And let’s not forget the famous story of Steve Jobs and Steve Wozniak creating the
arcade game Breakout which was also made entirely of TTL logic chips.
Of course digital computers were in existence as far back as the 1940s using vacuum tubes,
so needless to say they didn't have microprocessors either.
In fact, if you think about it, a microprocessor itself is nothing more than a bunch of transistors,
which in many cases can be separated into distinct sections of logic units.
Just as an example, the 6502 processor was recently recreated in large format with a
bunch of transistors and a lot of blinking LEDs to make it look cool and so you can see
what is going on inside of it.
They are calling it the Monster 6502.
So now I’ll introduce you to the Gigatron TTL microcomputer kit.
This is another do-it-yourself computer kit, similar to others I’ve featured on the channel
before.
But the main distinguishing difference is that this one has no microprocessor.
It comes in a very neat looking little box, and a fantastic manual.
I’ll go as far as to say this is the best manual I’ve ever seen for a project like
this.
And while it does contain a lot of in depth schematics and stuff, don’t let that scare
you away as the assembly instructions are actually really simple and anyone should be
able to assemble this.
In fact, the only tools you’ll really need is a soldering iron, preferably a good one,
some rosin core solder, and a pair of wire cutters.
And that’s it.
So, just taking a look at what it comes with, here’s a bag with most of the smaller components.
And here are all of the TTL logic chips, along with a RAM chip and an EPROM.
This appears to be a ubiquitous USB power cable.
And this is the board itself.
The layout on this board is spectacular and I can tell a lot of attention was taken to
make this look nice and be easy to assemble.
And down in the corner it says The Computer without microprocessor, along with the main
specifications.
I’m going to follow the assembly instructions in the manual and it says I should start by
installing these 40 little capacitors.
And so that’s what I’ll do!
There was a little confusion in the manual on how to install these diodes.
I had to read it several times.
So, hopefully this is right.
Well, the manual says at this point I can power it up, and if I see the test pattern
flashing on the LEDs, then everything is working so far, and it looks like it is.
So I guess I got the diodes in right.
Next, I’ll install the audio output.
And we’ll need the joystick port.
And the last thing is the VGA port, along with the various circuitry that goes along
with that.
After spending many hours assembling this, it was time to actually test it for video
output.
So, crossing my fingers.
Hey it works!
So for final assembly, I just need to install these rubber feet on the bottom of the case,
and then 4 more rubber feet go inside the box at the corners.
The board actually rests on these.
And then I can just insert the board and close it up.
It’s definitely a thing of beauty!
Well, let’s see what we can do with it.
When you first power it up you get a menu of some test programs you can try out.
I’m going to start with pictures.
Interesting..
some kind of ape.
I’m not sure which species.
Anyway, the Gigatron can display 64 colors because it has 2 bits for each of the RGB
channels, which I noticed when I was soldering in the resistors.
And while the resolution is very low, the colors are actually quite nice.
So let’s talk about the video display a bit.
The Gigatron can display a video resolution of 160 by 120 pixels, which is less than most
8-bit computers.
However, the Gigatron doesn’t really have a video chip.
They’ve borrowed a page from the Sinclair ZX-81 and all of the video generation is handled
in software by the CPU.
Of course, in this case, I use the term CPU somewhat loosely.
And due to the clock speed of this machine compared to the speed of a VGA signal, 160
pixels is the best resolution that can be made.
If you’ll notice, every 4th scan line on the screen is black, giving it a sort of retro-appearance,
however, part of the reason for this is that during the black scan line, the CPU is free
to actually execute code instead of worrying itself with drawing screen data.
However, it is possible to disable this feature.
But first I’ll show you the Mandelbrot demonstration.
So this creates a fractal image on the screen.
It looks like it wouldn’t take very long, but this actually takes quite some time.
But one thing I wanted to show you is if you press the SELECT button on the controller,
it will toggle the scan lines to a more full looking mode, at the expense of losing CPU
cycles for program code.
And this is clearly obvious on a program like this because you can see how much it slows
down when this mode is enabled.
Even in the faster mode, it takes almost 20 minutes to draw out this fractal pattern.
There are a couple of games on here, the first one is snake.
And I haven’t entirely figured out the point of the game.
I’m not sure if I’m supposed to be collecting these dots or avoiding them.
The other game is called racer.
And I think the point is to simply see how long you can go without crashing.
So I want to take a moment to talk about the programming language for the Gigatron.
The CPU, if you can call it that, only supports 8 instruction codes.
By coincidence the PDP-8 was named what it was because it only supported 8 instructions
as well.
Even an old chip like the 6502 had 56 different instructions and processors from Intel at
the time had hundreds of different instructions.
Writing code with only 8 instructions is certainly possible, but would be very tedious.
And so what they have done is created a virtualized environment.
So, imagine for example, if you look at how computers were done in the 1980s, like an
old Apple or Commodore, and if you imagine the hardware layer, this is the actual CPU
itself, which must be programmed in machine language.
Then they wrote a BASIC interpreter that is written in machine language, but allows a
BASIC program to run and a more friendly environment for the user to operate in.
Well, the Gigatron does something similar to this.
It also has the hardware layer, but then a virtual CPU is running on the hardware, which
is written in the native machine code, but it interprets the user software which is written
in something called GCL, which stands for Gigatron Control Language.
The language is still very similar to assembly language but it does at least have 34 instructions
making it easier to code for.
You might compare it to Steve Wozniak’s Sweet 16 language in this regard.
The CPU runs at 6.25 mhz, but by the time you take into account this virtual system
you’re probably getting something closer to 1 MHz which is more similar to home computers
from the 1980s.
So, while the Gigatron is pretty cool from a proof of concept and from an educational
standpoint, it does have some flaws, which I’m going to have to point out.
For one thing, it’s not cheap.
Now, computer manufacturers figured out a long time ago that the way to make computers
cheaper was to reduce the chip count, not to increase it.
And so, this computer with the number of chips it has, and the size of the logic board and
all of the different holes and traces on it, means its not cheap.
It retails for 160 Euros, which at the current conversion rate is almost $200 US dollars.
And that in and of itself wouldn’t be so bad, except the second problem.
And this is of course, just my subjective opinion, but the truth is, once you’ve finished
assembling the computer and you’ve explored all of the built in software, there’s not
a lot you can actually do with it.
There’s no way.
There’s no keyboard interface and there’s no way to actually program the Gigatron from
the computer itself.
There is a feature called loader on the main menu that will load new software in, but it
requires using an Arduino and of course doing all of the coding on an actual modern PC.
And so I think that’s a big drawback, and thus loses a lot of the fun that could be
had from experimenting with it.
However, that issue is mainly just a software issue.
And who knows?
They could update the firmware at some point to include some sort of command prompt, maybe
even run BASIC or at least some kind of machine language monitor.
So, is it worth the money?
I guess you’ll have to decide for yourself.
Myself, I’m just happy I was able to show you the product because I do think it’s
pretty interesting and I hope you found it interesting.
However, I’m still hoping somebody will build my dream computer.
And rather than go into that here, I’ll put a link down in the description to an article
on my website showing what I think my dream hobby computer would be.
And maybe somebody will build it.
So that about wraps it up for this episode.
So stick around until next time and as always, thanks for watching!