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What ever happened to Tandem and NonStop OS 2088

What ever happened to Tandem and NonStop OS 2090
Hm. Seems that I was reading the wrong system's manpages again. The other one didn't go into that much detail. At any rate, a whole bunch of things typically found on a Linux desktop installation...


I wrote this up yesterday, but for some reason it apparently got lost in the aether. If two versions show up, sorry.

What ever happened to Tandem and NonStop OS 2089
It actually requires "IO" to update the access time. man 2 stat ... The field statime is changed by file accesses, e.g. by execve(2), mknod(2), pipe(2), utime(2) and...

"Incident-wave" signalling essentially means that the signaling is off the first pbutting, if you will, of the wave to the receiver. "Reflected-wave" is used to describe a signaling means where the signal is valid on the bounce (reflection) from the end of the transmission line.

Basically, MCA is an end-terminated transmission system. There are terminators at the end of the T-line that absorb the signal's transition. PCI uses source-termination, where the signal is driven onto the line, it bounces off the unterminated end, then is absorbed in the terminator at the *source*. The first incidence of this wave in the middle of this line has a step in it and is unreliable for signaling (we can't be sure if it's a '1' or '0'). The reflected signal is full voltage and is reliable.

PCI signaling requires this bounce (reflection), MCA doesn't (it's not there). Each load (stub) on the line adds its own reflection on the bus, so care must be taken to ensure the required reflection is there and others are minimized.

The primary advantage of source-termination over end-termination is power. The end-terminator dissipates power since there is vlotage across it (Vline-Vtermination). The source terminator doesn't dissipate any DC power since there is no voltage across it other than during transitions (Vdriver-Vline). Source termination is flakey for multi-drop busses though because of the step in the signal. In fact PCI is the only place I've seen source termination used on a multi-drop bus. For point-to-point interfaces (no receivers in the middle that see the step) it makes a lot of sense.

-- Keith

What ever happened to Tandem and NonStop OS 2091
When I did the FreeBSD VM mgmt algorithms (upgraded from the original MACH stuff), I made...

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