TUHS

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Re: [TUHS] Questions for TUHS great minds

by Nelson H. F. Beebe

Tim Bradshaw <tfb(a)tfeb.org> writes on 17 Jan 2017 13:09 +0000 >> I think we've all lived in a wonderful time where it seemed like >> various exponential processes could continue for ever: they can't. For an update on the exponential scaling (Moore's Law et al), see this interesting new paper: Peter J. Denning and Ted G. Lewis Exponential laws of computing growth Comm. ACM 60(1) 54--65 January 2017 https://doi.org/10.1145/2976758 ------------------------------------------------------------------------------- - Nelson H. F. Beebe Tel: +1 801 581 5254 - - University of Utah FAX: +1 801 581 4148 - - Department of Mathematics, 110 LCB Internet e-mail: beebe(a)math.utah.edu - - 155 S 1400 E RM 233 beebe(a)acm.org beebe(a)computer.org - - Salt Lake City, UT 84112-0090, USA URL: http://www.math.utah.edu/~beebe/ - -------------------------------------------------------------------------------

8 years, 5 months

Re: [TUHS] TUHS Digest, Vol 14, Issue 63

by Doug McIlroy

> One thing that I'm unclear about is why all this Arpanet work was not filtering more into the versions of Unix done at Bell Labs. The short answer is that Bell Lbs was not on Arpanet. In the early 80s the interim CSNET gave us a dial-up window into Arpanet, which primarily served as a conduit for email. When real internet connection became possible, network code from Berkeley was folded into the research kernel. (I am tempted to say "engulfed the research kernel", for this was a huge addition.) The highest levels of AT&T were happy to carry digital data, but did not see digital as significant business. Even though digital T1 was the backbone of long-distance transmission, it was IBM, not AT&T, that offered direct digital interfaces to T1 in the 60s. When Arpanet came along MCI was far more eager to carry its data than AT&T was. It was all very well for Sandy Fraser to build experimental data networks in the lab, but this was seen as a niche market. AT&T devoted more effort to specialized applications like hotel PBXs than to digital communication per se. Doug

8 years, 5 months

2.11 pcc with ANSI?

by Andy Valencia

I'm having a lot of fun with a virtual 11/94 and 2.11. What a lot of excellent engineering! It seems like an obvious project would be to adapt a newer pcc with ANSI C support of some sort. Has this already been done? I'll take a look if not. Thanks, Andy Valencia p.s. The "less" in /usr/local doesn't seem to handle stty based TTY geometry. I re-ported "less2" from comp.sources.unix and added this. Somebody ping me if the mildly edited sources are of interest.

8 years, 5 months

Re: [TUHS] TUHS Digest, Vol 14, Issue 63

by jnc＠mercury.lcs.mit.edu

> From: Larry McVoy > It is pretty stunning that the company that had the largest network in > the world (the phone system of course) didn't get packet switching at > all. Actually, it's quite logical - and in fact, the lack of 'getting it' about packets follows directly from the former (their large existing circuit switch network). This dates back to Baran (see his oral history: https://conservancy.umn.edu/handle/11299/107101 pg. 19 and on), but it was still detectable almost two decades later. For a variety of all-too-human reasons (of the flavour of 'we're the networking experts, what do you know'; 'we know all about circuit networks, this packet stuff is too different'; 'we don't want to obsolete our giant investment', etc, etc), along with genuine concerns about some real issues of packet switching (e.g. the congestion stuff, and how well the system handled load and overload), packet switching just was a bridge too far from what they already had. Think IBM and timesharing versus batch and mainframe versus small computers. Noel

8 years, 5 months

Re: [TUHS] PDP-11, Unix, octal?

by jnc＠mercury.lcs.mit.edu

> From: Warren Toomey > Something I've been meaning to ask for a while: why Unix and octal on > the PDP-11? Because of the DEC documentation? Yeah, DEC did it all in octal. > I understand why other DEC architectures (e.g. PDP-7) were octal: 18b > is a multiple of 3. But PDP-11 is 16b, multiple of 4. Look at PDP-11 machine code. Two-op instructions look like this (bit-wise): oooossssssdddddd where 'ssssss' and 'dddddd' (source and destination) have the same format: mmmrrr where 'mmm' is the mode (things like R, @Rn, etc) and 'rrr' is the register number. All on octal boundaries. So if you see '010011' in a dump (or when looking at memory through the front console switches :-), you know immediately that means: MOV R0, @R1 Much harder in hex... :-) Noel

8 years, 5 months

Article on 'not meant to understand this'

by Warren Toomey

http://thenewstack.io/not-expected-understand-explainer/ in case you haven't seen it yet. Cheers, Warren

8 years, 5 months

Re: [TUHS] Article on 'not meant to understand this'

by jnc＠mercury.lcs.mit.edu

> From: Angelo Papenhoff > The problem is that the function which did the savu was not necessarily > the same as the function that does the retu, so after retu the function > could have the call stack of a different function. As dmr explained, > this worked with the PDP-11 compiler but not with the interdata > compiler. To put it slightly differently, in PDP-11 C all stack frames look identical, but this is not true of other machines/compilers. So if routine A called savu(), and routine B called aretu(), when the call to aretu() returned, procedure B is still running, but on procedure A's stack frame. So on machines where A's stack frame looks different from B's, hilarity ensues. (Note that aretu() was significantly different from retu() - the latter switched to a different process/stack, whereas aretu() did a 'non-local goto' [technically, switched to a different stack frame on the current stack] in the current process.) > Note that Lions doesn't explain this either, he assumed that the > difficulty was with with u_rsav and u_ssav .. (he probably wasn't that > wrong though, it really is confusing, but it's just not what the comment > refers to) Right. There are actually _three_ sets of saved stack info: int u_rsav[2]; /* save r5,r6 when exchanging stacks */ int u_qsav[2]; /* label variable for quits and interrupts */ int u_ssav[2]; /* label variable for swapping */ and it was the interaction among the three of them that I found very hard to understand - hence my (incorrect) memory that the 'you are not' comment actually referred to that, not the savu/aretu stuff! Calls to retu(), the primitive to switch stacks/processes, _always_ use rsav. The others are for 'non-local gotos' inside a process. Think of qsav as a poor man's exception handler for process software interrupts. When a process is sleeping on some event, when it is interrupted, rather than the sleep() call returning, it wakes up returning from the procedure that did the savu(qsav). (That last is because sleep() - which is the procedure that's running when the call to aretu(qsav) returns - does a return immediately after restoring the stack to the frame saved in qsav.) And I've forgotten exactly how ssav worked - IIRC it was something to do with how when a process is swapped out, since that can happen in a number of ways/places, the stack can contains calls to various things like expand(), etc; when it's swapped back in, the simplest thing to do is to just throw that all away and have it go back to where it was just before it was decided to swap it out. Noel

8 years, 5 months

Re: [TUHS] Early Internet work (Was: History of select(2))

by jnc＠mercury.lcs.mit.edu

> From: Tony Finch This is getting a bit far afield from Unix, so my apologies to the list for that. But to avoid dumping it in the Internet-History list abruptly, let me answer here _briefly_ (believe it or not, the below _is_ brief). > AIUI there were two major revisions to the IPv4 addressing architecture: Not quite (see below). First, one needs to understand that there are two different timelines for changes to addressing: in the hosts, and in the routers (called 'gateways' originally). To start with, they were tied together, but as of RFC-1122, they were formally separated: hosts no longer fully understood the syntax/semantics of addresses, just (mostly) treated them as opaque 32-bit quantities. > subnetting (RFC 917, October 1994 ... RFC 950, August 1985), and > classless routing (RFC 1519, September 1993) Originally, network numbers were 8 bits, and the 'rest' (local) part was 24. Mapping from IP addresses to physical network addresses was some with direct mapping - ARP did not exist - the actual local address (e.g. IMP/Port) was contained in the 'rest' field - each network had a document which specified the mapping. (Which is part of the interoperability issue with old implementations.) As some point early on, it was realized that 8 bits of network number were not enough, and the awful A/B/C kludge was added (it was dropped on the community, not discussed before-hand). Subnetting was indeed the next change. Then the host/router split happened. Classless routing (which effectively extended addesses, for path-computation purposes, to 32+N bits - since you couldn't look at a 32-bit IP address and immediately tell which was the 'network' part any more, you _had_ to have the mask as well, to tell you how many bits of any given address were the network number) was more of a process than a single change - the inter-AS routing (BGP) had to change, but so did IGP's (OSPF, IS-IS), etc, etc. > originally called supernetting (RFC 1338, June 1992). There was this effort called ROAD which produced RFC-1338 and 1519, and IIRC there was an intermediate, involving blocks of network numbers (1338), and that slowly evolved into arbitrary blocks (1519). One should also note that the term "super-netting" comes from a proposal by Carl-Hubert ("Roki") Rokitansky which did not, alas, make it to RFC. (His purpose was different, but it used the same mechanism.) Alas, the authors of 1338/1519 failed to properly acknowledge his earlier work. Noel

8 years, 5 months

Re: [TUHS] Early Internet work (Was: History of select(2))

by jnc＠mercury.lcs.mit.edu

> From: Johnny Billquist >> everyone working on TCP/IP heard about Version 4 shortly after the >> June, 1978 meeting. > Over a year before any documents said anything about it. Incorrect. It's documented in IEN-44, June 1978 (written shortly after the meeting, in the same month). > I'm sure people were doing networking protocols and stuff earlier, but > it wasn't the TCP/IP we know and talk about today People were working on Unix in 1977, but it's not the same Unix we know and talk about today. Does that mean it's not Unix they were working on? >> there were working implementations (as in, they could exchange data with >> other implementations) of TCP/IPv4 by January 1979 - see IEN 77. ^^ > But not TCP4 then. I just specified that it was v4 (see above). > thus, not interoperable with an implementation today No, with properly-chosen addresses (because of the changes in address handling), they probably would be. Noel

8 years, 5 months

Re: [TUHS] Early Internet work (Was: History of select(2))

by jnc＠mercury.lcs.mit.edu

> From: Paul Ruizendaal > I guess by April 1981 (RFC777) we reach a point where things are > specified to a level where implementations would interoperate with > today's implementations. Yes and no. Earlier boxes would interoperate, _if addresses on each end were chosen properly_. Modern handling of addresses on hosts (for the 'is this destination on my physical network' step of the packet-sending algorithm) did not come in until RFC-1122 (October 1989); prior to that, lots of host code probably tried to figure out if the destination was class A, B or C, etc, etc. Also, until RFC-826 (ARP, November 1982) pretty much all the network interfaces (and thus the code to turn the 'destination IP address' into an attached physical network address, for the first hop) were things like ARPANet that no longer exist, so you could't _actually_ fire up one of them unless you do something like the 'ARPANet emulation' that the various PDP-10 simulators use to allow old OS's running on them to talk to the current Internet. > only if one accepts IEN54/55 as 'TCP/IP' What are they, if not TCP/IP? Not the modern variant, of course, but then again, nothing before the early 90's is truly 'modern TCP/IP'. > IEN98 mentions a TCP3 stack done for Network Unix ... in 1978 by DTI / > Gary Grossman. I read this, BITD, but don't recall much about it. I was not impressed by the coding style. > at the same time it also uses old-style assignments ('=+' instead of > '+='). Could this be "typesetter C"? I don't know. IIRC, that compiler supported both styles. It had to have been a later compiler than the one that came with V6, that didn't support longs. But I don't recall any bug with long support in the typetter C compiler we had at MIT. > From the above I would support the moniker "first TCP/IP in C on Unix" No. That clearly belongs to the DTI one. (The difference between V3 and V4, while significant, aren't enough to make the DTI not 'TCP/IP in C for Unix'.) If you want to say 'first V4TCP/IP in C for Unix', maybe; I'd have to look for dates on the one done at MIT for V6, that may be earlier, but I don't think so. (Check the minutes in the IEN's, that's probably the best source of data on progress of the various implementations.) > One thing that I'm unclear about is why all this Arpanet work was not > filtering more into the versions of Unix done at Bell Labs. Here's my _guess_ - ask someone from Bell for a sure answer. You're using 20/20 hindsight. At that point in time, it was not at all obvious that TCP/IP was going to take over the world. There were a couple of alternatives for moving data around that Bell used - Datakit, and UUCP - and they worked pretty well, and there was no reason to pick up on this TCP/IP thing. I suspect that it wasn't until LAN's became popular than TCP/IP looked like a good thing to have - it fits very well with the capabilities most LANs had (in term of the service provided to things attached to them). Datakit was its own thing, and for UUCP you'd have to provide a reliable stream, and TCP/IP 'just did that'. Noel

8 years, 5 months

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