Hacker News Reader

Comment by logbiscuitswave | Hacker News Reader

Is there an ELI5 explanation for what is being shown here? It seems pretty fascinating even if I don’t quite understand it.

View on HN

The S100 bus was the first standard microcomputer bus[1]. It was based off of a passive mainboard system, so the CPU was just another card that plugged into it. The overwhelming majority of microcomputers that shipped with CP/M (as well as many that shipped with other operating systems) were based off of the S100 bus.

While there was never a commercial S100 board with a 486 on it, this article shows how it is fairly easy to design and build one.

S100 predates the PC bus, which largely replaced it. The AT (a.k.a ISA bus) was a 16-bit version of the 8-bit PC bus. IBM tried to get everyone to switch to the MCA bus, but the high royalties they charged meant that pretty much everone stuck with the AT bus until PCI came out. In its server form of PCI-X, PCI maxed out at 64-bits and 133MHz (though 32-bits and 66MHz was what you would see in a PC), and was replaced by PCIe, which is still used today.

Graphics cards were treated specially at several points along the way, with the VL-bus, and AGP basically being ISA and PCI respectively with dedicated higher-throughput buses to avoid having to use the more expensive MCA and PCI-X when the graphics card was the sole device in the system that needed higher bandwidth.

> pretty much everone stuck with the AT bus until PCI came out

There was also EISA which was quite popular as an alternative to MCA until PCI bedded itself in.

https://en.wikipedia.org/wiki/Extended_Industry_Standard_Arc...

I particularly enjoyed this (possibly apocryphal bit):

"when it became clear to IBM that Micro Channel was dying, IBM licensed EISA for use in a few server systems."

I forgot about that. Interesting how 2 generations in a row basically followed the same pattern of commodity, server, high-speed commodity:

ISA, EISA, VLB PCI, PCI-X, AGP

Crikey, I'd forgotten about AGP, though that was specifically for graphics cards (as was VLB) rather than being general purpose.

I remember having both AGP and VLB graphics cards at one time or another. Definitely got the short end of that stick when PCI came along and became the de facto standard.

I do seem to recall for a short period of time there were some motherboards with both PCI and AGP slots for those who really needed that level of interoperability.

AGP superceded PCI for graphics. It was based on PCI and was a dedicated link that received multiple increases in speed over its lifetime. AGP, 2x, 4x, 8x. Etc. Boards with PCI and AGP were very common. You could even find ones with ISA, PCI, and AGP.

I own an inoperable relic which has an EISA bus, SCSI card, advanced VGA card, Colorado tape drive, Zip Drive, and a fair amount of RAM to support a 486DX-50. I ran DOS, Windows 3.11, and OS/2 2.0 on it at various times. I may have tried out Windows NT 3.something too. These components and the EISA bus itself were standard enough to be supported by that range of OS's.

That's funny - I am sure I had an issue of Computer Shopper that had all of those items circled in felt pen ...

For VL-bus many systems included 2 slots. One for a graphics card and the other for a storage controller. The VL-bus was basically a direct attachment to the 486 memory bus.

Also there was Extended ISA (EISA) which was a standard promoted by PC compatible manufacturers to compete with MCA. It added 32 bit support and bus mastering to the ISA bus. I and 16 bit ISA cards would still work in an EISA slot. It never really caught on for desktops but briefly had wide support in servers.

Thanks! I’m very familiar with PCish buses going back to the AT bus days, but I had never heard of the S100 bus before. I’m pretty amazed at just how versatile it is.

Appears the 80486 can be connected to the S100 bus directly given ability to read from adjustable size databus.

This means effectively an x86 style cpu can be part of a simple computer design

It's the website for the s-100 bus that the processors it talks about works with,(i.e, 80486 intel processors). It's a lot of nostalgic 1989 bus verbiage for uber geeks and engineers who make that stuff.

It's kinda amazing how many processors have been put on the bus. The guy who runs the site has built[1] a huge number of both CPU and peripheral boards. The S100 bus sure has an outsized shadow.

[1]http://www.s100computers.com/My%20System%20Index%20Page.htm

Reply on news.ycombinator.com