How early 8-bit arcade machines differed in design from 8-bit home computers • Hacker News Board

Re: How early 8-bit arcade machines differed in design from 8-bit home computers

#11

Post by tom_ » Tue, Oct 09, 2018, 11:13 AM UTC

axilmar wrote: post #3

I will forever wonder why 8-bit computers of the 80s didn't have more powerful video hardware. It's not that the technology wasn't available, since most arcade machines at the time had a lot more powerful graphics hardware than 8-bit home machines. (I will also forever wonder why Sega's 16-bit console didn't have hardware sprite scaling and rotation, since that was the main attraction of Sega games at the time...) I…

It would have been quite a lot more expensive, I assume? Roughly speaking, with 2MHz RAM, and assuming a setup where the CPU and the display system alternate (so 1,000,000 bytes/second bandwidth for each), you have a budget of 40 bytes for the visible part of the line, and large buffers are expensive, so it's just a question of how you spend it. Take the C64 as an example: you've got 320 px mono (40 bytes/line), 160 px 2bpp (40 bytes/line), or 2 40-byte character modes (40 bytes/line). I assume the fetches for the 8 sprites fit in the 24 bytes that are left, as each is 3 bytes wide.

Later machines had more bandwidth and more complicated memory systems, but the limitations are still the same. You have a fixed number of bytes you can fetch from RAM per second, the TV scans out at a certain rate, and that's going to limit what you can do.

Re: How early 8-bit arcade machines differed in design from 8-bit home computers

#12

Post by flohofwoe » Tue, Oct 09, 2018, 11:20 AM UTC

amadvance wrote: post #9

He made me smile when he says: "there’s very little information for Bomb Jack on the web" hardware schematics, dumped rom, source of a working emulator... What do you want more ? :)

Compared to the wealth of information and research that's available for popular machines like the CPC, ZX or C64 that's indeed not much :) But true, since Bomb Jack is only built from well-known standard parts, the schematics is all that's needed (although there are some minor problems in it, like missing or faulty labels).

Re: How early 8-bit arcade machines differed in design from 8-bit home computers

#13

Post by mrob » Tue, Oct 09, 2018, 11:48 AM UTC

tom_ wrote: post #11

axilmar wrote: post #3

I will forever wonder why 8-bit computers of the 80s didn't have more powerful video hardware. It's not that the technology wasn't available, since most arcade machines at the time had a lot more powerful graphics hardware than 8-bit home machines. (I will also forever wonder why Sega's 16-bit console didn't have hardware sprite scaling and rotation, since that was the main attraction of Sega games at the time...) I…

It would have been quite a lot more expensive, I assume? Roughly speaking, with 2MHz RAM, and assuming a setup where the CPU and the display system alternate (so 1,000,000 bytes/second bandwidth for each), you have a budget of 40 bytes for the visible part of the line, and large buffers are expensive, so it's just a question of how you spend it. Take the C64 as an example: you've got 320 px mono (40 bytes/line), 160…

That's assuming you're reading all the layers from the same ram. You could increase memory bandwidth by using separate chips for each layer.

Re: How early 8-bit arcade machines differed in design from 8-bit home computers

#14

Post by sehugg » Tue, Oct 09, 2018, 11:59 AM UTC

tom_ wrote: post #11

axilmar wrote: post #3

I will forever wonder why 8-bit computers of the 80s didn't have more powerful video hardware. It's not that the technology wasn't available, since most arcade machines at the time had a lot more powerful graphics hardware than 8-bit home machines. (I will also forever wonder why Sega's 16-bit console didn't have hardware sprite scaling and rotation, since that was the main attraction of Sega games at the time...) I…

It would have been quite a lot more expensive, I assume? Roughly speaking, with 2MHz RAM, and assuming a setup where the CPU and the display system alternate (so 1,000,000 bytes/second bandwidth for each), you have a budget of 40 bytes for the visible part of the line, and large buffers are expensive, so it's just a question of how you spend it. Take the C64 as an example: you've got 320 px mono (40 bytes/line), 160…

Arcade games could also more readily use ROM, so tile and sprite data could just flow in parallel to the rendering subsystem -- without worrying about sharing with the CPU or refresh cycles.

Re: How early 8-bit arcade machines differed in design from 8-bit home computers

#15

Post by tom_ » Tue, Oct 09, 2018, 12:01 PM UTC

mrob wrote: post #13

tom_ wrote: post #11

Earlier quoted context omitted.

It would have been quite a lot more expensive, I assume? Roughly speaking, with 2MHz RAM, and assuming a setup where the CPU and the display system alternate (so 1,000,000 bytes/second bandwidth for each), you have a budget of 40 bytes for the visible part of the line, and large buffers are expensive, so it's just a question of how you spend it. Take the C64 as an example: you've got 320 px mono (40 bytes/line), 160…

That's assuming you're reading all the layers from the same ram. You could increase memory bandwidth by using separate chips for each layer.

Yes, and the C64's colour RAM is a good example, because accesses to it come for free on top of the 64 bytes/line from the main RAM. But more chips is exactly the sort of thing that would make it more expensive. And I assume it would also have been more complex to build, or something - because if it were cheap and easy, surely people would have done it?

Re: How early 8-bit arcade machines differed in design from 8-bit home computers

#16

Post by psykotic » Tue, Oct 09, 2018, 12:05 PM UTC

mrob wrote: post #13

tom_ wrote: post #11

Earlier quoted context omitted.

It would have been quite a lot more expensive, I assume? Roughly speaking, with 2MHz RAM, and assuming a setup where the CPU and the display system alternate (so 1,000,000 bytes/second bandwidth for each), you have a budget of 40 bytes for the visible part of the line, and large buffers are expensive, so it's just a question of how you spend it. Take the C64 as an example: you've got 320 px mono (40 bytes/line), 160…

That's assuming you're reading all the layers from the same ram. You could increase memory bandwidth by using separate chips for each layer.

Memory usually accounted for a majority of the cost in those days, so there's a lot to be said for a unified memory system in home computers. The standard memory architecture for home computers from 8-bits like C64 to 16-bits like Amiga was unified memory with half the memory cycles each going to the CPU and graphics, and PCM playback on later systems could conveniently steal a few graphics memory cycles during hblank. (The C64's VIC-II also stole CPU memory cycles every 8 scanlines and could be forced into stealing a lot more bandwidth with the 'badlines' technique.) ROM-based arcade machines and consoles generally had memory parallelism for their graphics systems. It puts heavy pressure on the chip pin-out and it requires you to physically allocate the RAM/ROM chips onto different buses. I guess theoretically you could put all the memory chips on multiple buses with a configurable arbiter in front of each so you could change the allocation per application, but the PCB for that would be massive and expensive. Instead there was usually a slow, awkward way to access memory from a different bus, e.g. the graphics bus could be accessed by the CPU only with DMA or a pair of memory-mapped addr/data registers with multi-cycle wait states. So, this kind of architecture isn't really suitable for a general-purpose home computer unless you can afford a large allowance of memory for each bus, but it did exist on high-end home computers like the X68000 that were less cost constrained. Also, Amiga did have the option for a kind of RAM expansion called Fast RAM which was only accessible to the CPU, unlike normal Chip RAM which was accessible on the standard chipset bus to the audio and graphics chips in addition to the CPU. Fast RAM didn't speed up the graphics system but it prevented the CPU from stalling when the other chips wanted to steal CPU memory cycles on the chipset bus (they always take precedence since they have hard real-time constraints).

Re: How early 8-bit arcade machines differed in design from 8-bit home computers

#17

Post by taneq » Tue, Oct 09, 2018, 12:07 PM UTC

pkiller wrote: post #4

axilmar wrote: post #3

I will forever wonder why 8-bit computers of the 80s didn't have more powerful video hardware. It's not that the technology wasn't available, since most arcade machines at the time had a lot more powerful graphics hardware than 8-bit home machines. (I will also forever wonder why Sega's 16-bit console didn't have hardware sprite scaling and rotation, since that was the main attraction of Sega games at the time...) I…

It's my understanding, that the reason why arcade boards were so much more powerful was because they were a lot more complex thus much more expensive to design, source components and produce in large scale. More colors, background layers and sprites with slow CPUs and graphics chips in the 80s usually meant having several RAM chips to have multiple memory buses and parallel accesses to video memory and more video mem…

All of this, plus an arcade machine was specialised. BomberMan needs 39 sprites?[1] Build the hardware to do that! Super Racer needs 3D polygonal graphics? Add a hardware scanline rasterizer. To put all these tricks into a home computer, though, would have made it cost many times as much as an arcade cabinet.

[1] Not real numbers.

Re: How early 8-bit arcade machines differed in design from 8-bit home computers

#18

Post by growlist » Tue, Oct 09, 2018, 12:15 PM UTC

Ah, Bomb Jack. I loved playing this game on my Spectrum, had a MAME version in 2001 while studying my masters, and now it runs perfectly in a browser. Amazing. As is often the way with procrastination I became pretty skilled at my chosen distraction, memorising all the patterns with which to get a high score. Let's see how much I can remember!

Re: How early 8-bit arcade machines differed in design from 8-bit home computers

#19

Post by okyougotmenow » Tue, Oct 09, 2018, 12:36 PM UTC

axilmar wrote: post #3

I will forever wonder why 8-bit computers of the 80s didn't have more powerful video hardware. It's not that the technology wasn't available, since most arcade machines at the time had a lot more powerful graphics hardware than 8-bit home machines. (I will also forever wonder why Sega's 16-bit console didn't have hardware sprite scaling and rotation, since that was the main attraction of Sega games at the time...) I…

Arcade cabinets are the wrong comparison. Better are home consoles, in particular the NES/Famicom. A fine-scrollable tilemapped background + hardware sprite multiplexing made it trivial to develop games for the Famicom that would be technological marvels on contemporary home computers, yet no western computer manufacturer came up with that design, despite being small additions on top of text-mode graphics and hardware sprites.

Re: How early 8-bit arcade machines differed in design from 8-bit home computers

#20

Post by laumars » Tue, Oct 09, 2018, 1:06 PM UTC

okyougotmenow wrote: post #19

axilmar wrote: post #3

I will forever wonder why 8-bit computers of the 80s didn't have more powerful video hardware. It's not that the technology wasn't available, since most arcade machines at the time had a lot more powerful graphics hardware than 8-bit home machines. (I will also forever wonder why Sega's 16-bit console didn't have hardware sprite scaling and rotation, since that was the main attraction of Sega games at the time...) I…

Arcade cabinets are the wrong comparison. Better are home consoles, in particular the NES/Famicom. A fine-scrollable tilemapped background + hardware sprite multiplexing made it trivial to develop games for the Famicom that would be technological marvels on contemporary home computers, yet no western computer manufacturer came up with that design, despite being small additions on top of text-mode graphics and hardwar…

Some western micro computers did have some of that though. The C64 did have hardware scrolling, which is why you see a higher calibre of scrolling games on that machine than you would on the Amstrad CPC 464 (which did not have hardware scrolling).

It all comes down to expense though. You could throw the whole kitchen sink into the computer but then how much would it cost to manufacture and how much would you need to sell the thing for?

Costs need to be cut somewhere and micro computers had to additionally ship an interpreter ROM (typically some dialect of BASIC), more expansions ports (for printers, serial modems, memory expansions, additional storage devices, etc) a physical keyboard, and so on.

Plus lets also not forget that while many micros were sold as games machines - they were originally built as hybrid devices for doing work, finances, etc as well as recreation.