Of the machines from the 16-bit era, the Commodore Amiga arguably has the most active community decades later, and it’s a space which still has the power to surprise. Today we have a story which perhaps pushes the hardware farther than ever before: a demo challenge for the Amiga custom chips only, no CPU involved.
The Amiga was for a time around the end of the 1980s the most exciting multimedia platform, not because of the 68000 CPU it shared with other platforms, but because of its set of custom co-processors that handled tasks such as graphics manipulation, audio, and memory. Each one is a very powerful piece of silicon capable of many functions, but traditionally it would have been given its tasks by the CPU. The competition aims to find how possible it is to run an Amiga demo entirely on these chips, by using the CPU only for a loader application, with the custom chip programming coming entirely from a pre-configured memory map which forms the demo.
The demoscene is a part of our community known for pushing hardware to its limits, and we look forward to seeing just what they do with this one. If you have never been to a demo party before, you should, after all everyone should go to a demo party!
Amiga CD32 motherboard: Evan-Amos, Public domain.
This was actually copied from arcade machines and other game consoles, when the company first intended to make the machine into a game console. The chipset would have been the “CPU” of the machine and where the 68000 CPU sits would have been a ROM chip in a game cartridge, with the optional extra CPU with its own memory.
The designers pivoted it into a personal computer by doing exactly that: instead of a cartridge, a 68000 CPU and memory. That’s why there’s two memory buses and two different types of RAM. and the custom chipset sits in the midde of it.
If they had made it into a personal computer to begin with, they would have gone PC style with a common backplane bus between memory, CPU, and additional hardware, with the chipset present as an “accelerator” card.
The way it was originally supposed to work. The boot ROM initializes the chipset to read off the game ROM and then Bob’s your uncle. They’re just starting with the data in chip RAM.
Tell me you don’t know anything about building PCs without telling me you don’t know anything about building PCs /s
RAM and PCI-X buses are not connected together, you can’t plug you GPU into a RAM socket, it won’t work.
Where did I say so?
Also note that while today on a PC we have bridge controllers (“chipsets”, north bridge, south bridge) to address peripheral buses and other hardware, in the original IBM PC specs the CPU sits directly on the same bus as everything else and acts as the master controller. So in effect your RAM is on the same bus as your graphics card and you could, in theory, plug a GPU into a RAM socket.
https://image1.slideserve.com/3396245/pc-architecture-l.jpg
Part of the reason why the Amiga was supposed to be superior was because the chipset did the work of a bus controller, so the CPU didn’t have to. However, since so much of the functionality was tied and integrated to the chipset, it couldn’t be upgraded without breaking compatibility. Then PCs started introducing separate bus controllers to offload the task from the CPU, and the advantage was lost.
Not just that awful slow PC 5150, the IBM PC/AT Model 5170 was still same here, too.
IBM sold memory boards for AT bus, even.
https://minuszerodegrees.net/5170/cards/5170_cards.htm
Back in the day it was just normal that the processors’ front-side bus was connected to the expansion slots.
The concept of chipsets arose in an effort to dec-ouple the main processor and the expansions bus (and peripherals).
Another concept introduced with i486 was the use of clock-doubling.
The CPU would internally run twice the external speed.
PCI-X, along with PCIe which you meant to say, didn’t exist before the year 2000.
Not only can you plug a GPU into a RAM socket, but you won’t have much other choices for another 5 years when the industry moved the video memory back into the video chip again instead of used the much cheaper system dram.
Lastly by PC I can only assume you really do mean PC. This isn’t a PC. Even so, PCs absolutely do let you access memory boards on the ISA bus along with video cards. By this time IBM had a few pioneer examples to pick one to copy, and that’s exactly what they did.
“RAM and PCI-X buses are not connected together, you can’t plug you GPU into a RAM socket, it won’t work.”
kids these days don’t even know where we came from :)
Probably doable using both copper lists and modifying the inactive copper list from the active one. Tried something like that myself many years ago but I couldn’t quite get it working. I also included the blitter though, I think that was the part that failed
That’s not at all how the Amiga does or ever was designed to work.
Amiga didn’t “copy” anything from the arcade. Arcades used almost exclusively commodity parts from Zilog, TI, etc. The only thing custom about them were the ROMs and board layouts.
I wasn’t a computer designer, but I sure do miss my Amiga. I had the E plant board to run Mac emulation and it ran benchmarks faster that the SE30 did native. I could cut and paste from the Amiga side to the Mac emulation to the 386 board that I had running as well. With some care with partition permissions I could copy files from one environment to another.
I was a graduate student and the data analysis program I ran was written by a buddy and ran on the Mac. I wrote my thesis in AmigaTEX. I started on an A500, then the A2000, then an A3000. I gamed a little, not a lot.
The graphics performance was amazing.
Support for external video sync was great too. And while not exactly portable, I took my A500 to New Orleans and used my GFs TV as my monitor.
Of all the machines I ever used, the Amiga was my favorite. Commodore had no clue.
SLAC used them as real time graphical front ends for their IBM mainframes glueing it together with ARex. One time the IBM brain trust was out. Thier response? “We can’t do that.”
It’s no wonder the user community is still do strong. It was a unique machine with amazing capabilities. Add a Video Toaster and you had a recording studio.
What a time!