This is the video transcript. Read the original article with all the details →
Good morning and welcome to the ValorosoIT channel! We deal with vintage computers and electronics. We have Nicola Avanzi here with us! You already met him on the @ValorosoIT channel... but not face to face. He had helped me with the Commodore PC10, to expand the RAM memory. He gave me the necessary information, then I made a video. I'll put it in the description.
Well, we are at Varese Retrocomputing 2024 and Nicola has brought some very, very interesting machines. What are you telling us about?
Yes, I brought a line of computers from Digital Equipment Corporation, DEC, of personal computers that not everyone knows about. Because, in fact, DEC is famous for its minicomputers, for example the PDP, which made history in the 60s and 70s. At MIT, Bill Gates himself built and developed the BASIC for the Altair 8800 on the PDP-11. UNIX was born there, C was born on the PDP.
Well, you should know that, in the 1980s, after the release of the IBM XT PC, DEC decided to enter the personal computer market and did so with a couple of products. Actually, three products: the DEC Rainbow 100 and the DEC Professional 320, 350 and 380. DEC introduced this line of personal computers in 1982 and they were innovative for their time.
We can see, on the left, the DEC Rainbow 100, which is a personal computer compatible with MS-DOS, but not compatible with IBM PC. In fact, some of the programs are running, but not all of them, even if the software package envisaged was considerable. The peculiarity of this computer is that it has two processors: a Z80 and an Intel 8088, which coexist on the same motherboard with two separate 8-bit BUS and communicate with each other via a shared memory of 64KB. This allows you to run Digital's CP/M, called CP/M-86/80, which can independently execute both CP/M-80 programs, therefore 8-bit using the Z80, and 16-bit programs for CP/M-86. It allows you to run both 8-bit and 16-bit programs for the Intel 8088.
It is a particular architecture, because if you see, the motherboard does not have the classic ISA slots, like on the IBM XT. They are all cards mounted directly on the motherboard, up to covering it, technically in a sandwich.
Yes, that's right, until it completely covers the motherboard.
But I wanted to ask you, does the 8088 processor have the possibility to also install the math processor?
Subsequently, an expansion card was released that included installation, but basically no.
Basically no, huh? I ask because lately, in my videos, I always enjoy installing mathematical coprocessors on motherboards where they didn't exist, because they cost a lot of money back then. Now on AliExpress maybe you can buy it for 10-20 euros and then you can put all the things that you once couldn't afford.
In fact, in terms of architecture it is very particular, because it is not like the IBM PC. It does not have the 640KB limit, it is able to exploit up to 896KB of memory, precisely by design, and therefore it can be useful for slightly more robust applications, such as CAD drawing, but also software development with the compiler which is able to grind much more, because it is able to use all this memory.
Another gem of this computer line is its drive. The drive is a DEC RX50, we can take it if you want. This drive is better than the IBM (about the same size), which was a single 360KB drive. The RX50 is a dual 400KB drive. It is a very elegant product because it gives you the possibility, in the same space, of having two floppy drives inserted: one in the upper part and one in the lower part. Thus the drive is able to use two floppies, not at the same time, because it uses the same rotation shaft and the two heads are moved by the same movement system. So the track is unique.
Exactly, so we can read from A: and then write to B:, in short.
I recently designed a new memory card, which is this one. I took inspiration from a board that was built many years ago.
So this is yours? Yes, I designed this one. Ah, congratulations!
Because the first version of Rainbow 100, A, was expandable to a maximum of 256KB.
Ok, so you're really an expert on memory expansions, that's why you helped me with the Commodore PC10! I have fun with memory expansions!
How is it made? Here is the Intel 8088 processor. Exactly, precisely because in the first version of the Rainbow, the memory expansion connector did not have all the address lines, so it could not reach addresses up to 896KB. In this memory card, the processor was moved to the memory card and then reconnected via this socket to the motherboard.
Ah, interesting! This way we have access to all address lines.
I understand! So I had to rebuild the board this way.
You basically moved the processor from the motherboard to this board. This connector here ends up on the processor socket and here we have 1 MB of RAM, even though it uses 896KB of it. Yes, because the maximum addressing is right there. So part of the RAM is not used.
Beautiful, congratulations, I like it!
Here I see that we have AutoCAD. Yes, AutoCAD version 2 and something, but Windows also runs on it: Windows 1.0.
Ok, I had made a video, installing Windows 1.04, though. Instead AutoCAD, I had 2.6 when I was little, but for MS-DOS on an IBM PS/2. This comes a little earlier than, let's say, the IBM competitor XT. Try to think about an IBM 5150, with a maximum of 512KB of RAM, what could you do? This is truly a workstation for its time. In fact, it also had a very different cost. It came out with a base list price, without the hard disk, of $3000, which was... that is, not very affordable, in fact, not at all! But in companies something...
No, in fact, I think even more was spent in companies. Yes. And only towards the end of the 1980s, when it was discontinued by companies, did it also begin to arrive in homes, as a used computer.
In fact, MS-DOS 3.0 was later ported by Suitable Solutions. Expansion cards, memory cards and other things were later adapted. We saw the DEC Rainbow 100, which was let's say the entry level of DEC's personal computer series. Now let's see the professional product, where DEC aimed a little more: it is the DEC Professional line. The Professional line is interesting because it features the same chipset and microprocessor as the DEC PDP minicomputer series. So, let's say that it is the only PDP desktop computer that we can put on the desk, because even the micro PDP is still 30, 40, 50 KG and, of the others, the PDP-11/73 was still a full-bodied machine. This computer, therefore, has the same processor as the DEC PDP family: it is a 16-bit processor, with 22 address bits, it can address up to 4 MB of memory, which for the 80s was really a lot and allowed professional applications of a certain level.
Here, however, what is the operating system?
The operating system is window-based, completely unknown to most people - including me - and is called Synergy 2.0. It involves multitasking, in fact in this screen we see that there is a spreadsheet with a graph, below the calculator and below that we have a chess program running.
Ah, so now we would say... that's an Excel there!
Exactly, but it is not an Excel, it will be called something else.
Yes, that's right, the calculator remained that way. What is this here? Do we call it PowerPoint?
No, it is the graph generated by the Excel sheet.
Ah, so always Excel. And the game of chess, oh well, it's underneath. So can you then play with windows like you do with Windows today?
Exactly, but there was no mouse support.
Oh, so how do you do it?
There is a special break button in the menu that says move window, resize window, making the break. Going here, in Windows you have Move Windows, Change Size, or you can bring it to the front. It wasn't very comfortable, let's say, was it?
In fact, however, the idea was there. The idea was already there, in short.
But are we talking about what year here?
Well, this was already in the mid-80s. And so if desired, the mouse existed. Oh yeah, they just didn't implement it.
Exactly, because he was born with the operating system without windows, that Professional OS, which is essentially a limited version of RSX-11M Plus, which ran on the PDP-11, which we see here on the left, the reproduction.
Is this a reproduction?
It is a scale reproduction of the control panel, but let's say that it works more or less exactly, with limited compatibility, like the PDP. There is no panel, but behind it, in the parallel port, you can get a console where you can operate the commands as if you were above the ODT, the Online Debug Tool, of the panel.
So in the end it's more or less the same machine, but in short, a little optimised. I remember this one, the original one, much longer, later, right? The panel was much larger in size.
Yes, let it be wider, but then after that there is the computer behind it. Instead, in this case in here there will be... a Raspberry and SIMH, which is a PDP simulator.
If desired, there is also the possibility of mounting an FPGA, if one wants it more faithful to the original.
If you want it really realistic, the best thing is the Professional 380, which mounts a full-fledged PDP.
Or else one looks for it and buys it, spending what they have to spend.
Yes, but at least you don't have the problem of two wardrobes that you have to put in the house! Besides.
Thanks so much for all the information, Nicola. Thanks to you, it was a pleasure! I like to collaborate.
Oh yes, among the various retrocomputer enthusiasts.
Anyone interested in vintage computer topics, subscribe to the channel and activate the notification bell. Until the next video!
See you soon, bye!