TUHS

tuhs@tuhs.org

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6557 discussions

by Clem Cole

Cute article from a few days ago in the Telegram about DEC with some since pics that I thought I would pass on to this group. http://www.telegram.com/news/20171118/digital-equipment-born-60-years-ago-i…

7 years, 9 months

Re: [TUHS] Determining what was on a tape back in the day

by jnc＠mercury.lcs.mit.edu

> From: Will Senn > I don't quite no how to investigate this other than to pore through the > pdp11/40 instruction manual. One of these: https://www.ebay.com/itm/Digital-pdp-Programming-Card-8-Pages/142565890514 is useful; it has a list of all the opcodes in numerical order; something none of the CPU manuals have, to my recollection. Usually there are a flock of these "pdp11 Programming Cards" on eBait, but I only see this one at the moment. If you do any amount of work with PDP-11 binary, you'll soon find yourself recognizing the common instructions. E.g. MOV is 01msmr (octal), where 'm' is a mode specifier, and s and r are source and destination register numbers. (That's why PDP-11 people are big on octal; the instructions are easy to read in octal.) More here: http://gunkies.org/wiki/PDP-11_architecture#Operands So 0127xx is a move of an immediate operand. >> You don't need to mount it on DECTape drive - it's just blocks. Mount >> it as an RK05 image, or a magtape, or whatever. > I thought disk (RK05) and tape (magtape) blocks were different... Well, you need to differentiate between DECtape and magtape - very different beasts. DECtape on a PDP-11 _only_ supports 256 word (i.e. 512 byte) blocks, the same as most disks. (Floppies are an exception when it comes to disks - sort of. The hardware supports 128/256 byte sectors, but the usual driver - not in V6 or V7 - invisibly makes them look like 512-byte blocks.) Magtapes are complicated, and I don't remember all the details of how Unix handles them, but the _hardware_ is prepared to write very long 'blocks', and there are also separate 'file marks' which the hardware can write, and notice. But a magtape written in 512-byte blocks, with no file marks, can be treated like a disk; that's what the V6 distribution tapes look like: http://gunkies.org/wiki/Installing_UNIX_Sixth_Edition#Installation_tape_con… and IIRC 'tp' format magtape tapes are written the same way, hardware-wise (so they look just like DECtapes). Noel

7 years, 9 months

Re: [TUHS] Some resources for V6/PDP/SIMH newbs like me

by jnc＠mercury.lcs.mit.edu

> From: Will Senn > (e) UNIX assembler uses the characters $ and "*" where the DEC > assemblers use "#" and "@" respectively. Amusing: the "UNIX Assembler Reference Manual" says: The syntax of the address forms is identical to that in DEC assemblers, except that "*" has been substituted for "@" and "$" for "#"; the UNIX typing conventions make "@" and "#" rather inconvenient. What's amusing is that in almost 40 years, it had never dawned on me that _that_ was why they'd made the @->*, etc change! "Duhhhh" indeed! Interesting side note: the UNIX erase/kill characters are described as being the same as Multics', but since Bell pulled out of the Multics project fairly early, I wonder if they'd used it long enough to get '@' and '#' hardwired into their fingers. So I recently has the thought 'Multics was a follow-on to CTSS, maybe CTSS used the same characters, and that's how they got burned in'. So I looked in the "CTSS Programmer's Guide" (2nd edition), and no, according to it (pg. AC.2.02), the erase and kill characters on CTSS were '"' and '?'. So, so much for that theory! > (l) The names "_edata" and "_end" are loader pseudo variables which > define the size of the data segment, and the data segment plus the bss > segment respectively. That one threw me, too, when I first started looking at the kernel! I don't recall if I found documentation about it, or just worked it out: it is in the UPM, although not in ld(1) like one might expect (at least, not in the V6 UPM; although in V7: http://minnie.tuhs.org/cgi-bin/utree.pl?file=V7/usr/man/man1/ld.1 it is there), but in end(3): http://minnie.tuhs.org/cgi-bin/utree.pl?file=V6/usr/man/man3/end.3 Noel

7 years, 9 months

redirection wildness in v7

by Will Senn

Why does the first of these incantations not present text, but the second does (word is a file)? Neither errors out. $ <word | sed 20q $ <word sed 20q Thanks, Will -- GPG Fingerprint: 68F4 B3BD 1730 555A 4462 7D45 3EAA 5B6D A982 BAAF

7 years, 9 months

Re: [TUHS] UNIX on S/370

by jnc＠mercury.lcs.mit.edu

> From: Clem Cole <clemc(a)ccc.com> > IIRC Tom Lyons started a 370 port at Princeton and finished it at > Amdahl. But I think that was using VM Maybe this is my lack of knowledge of VM showing, but how did having VM help you over running on the bare hardware? Noel

7 years, 9 months

First permanent ARPAnet link

by Dave Horsfall

https://en.wikipedia.org/wiki/Leonard_Kleinrock#ARPANET ``The first permanent ARPANET link was established on November 21, 1969, between the IMP at UCLA and the IMP at the Stanford Research Institute.'' And thus from little acorns... -- Dave Horsfall DTM (VK2KFU) "Those who don't understand security will suffer."

7 years, 9 months

Re: [TUHS] Some resources for V6/PDP/SIMH newbs like me

by jnc＠mercury.lcs.mit.edu

> From: Will Senn > he is addressing an aspect that was not addressed in either of the > manual's entries and is very helpful for making the translation between > PDP-11 Macro Assembler and unix as. I'm curious - what aspect was that? Noel

7 years, 9 months

Re: [TUHS] Some resources for V6/PDP/SIMH newbs like me

by jnc＠mercury.lcs.mit.edu

> From: Will Senn <will.senn(a)gmail.com> > To bone up on assembly language, Lions's commentary is exceptionally > helpful in explaining assembly as it is implemented in V6. The manual > itself is really thin Err, which manual are you referring to there? Not the "UNIX Assembler Reference Manual": http://minnie.tuhs.org/cgi-bin/utree.pl?file=V6/usr/doc/as/as I would assume, but the 'as(I)' page in the UPM? Noel

7 years, 9 months

Re: [TUHS] Determining what was on a tape back in the day

by jnc＠mercury.lcs.mit.edu

> From: Will Senn > I'm off to refreshing my pdp-11 assembly language skills... A couple of things that might help: - assemble mboot.s and 'od' the result, so when you see something that matches in the dump of the 0th block, you can look back at the assembler source, to see what the source looks like - read the boot block into a PDP-11 debugger ('db' or 'cdb' on V6, 'adb' on V7; I _think_ 'adb' was available on V7, if not, there are some BSD's that have it) and use that to disassmble the code Noel

7 years, 9 months

Re: [TUHS] Determining what was on a tape back in the day

by jnc＠mercury.lcs.mit.edu

> The 0th block does seem to contain some PDP-11 binary - a bootstrap of > some sort. I'll look in more detail in a bit. OK, I had a quick look, and it seems to be a modified version of mboot.s: http://minnie.tuhs.org/cgi-bin/utree.pl?file=V6/usr/source/mdec/mboot.s I had a look through the rest of the likely files in 'mdec', and I didn't find a better match. I'm too lazy busy to do a complete dis-assembly, and work out exactly how it's different, though.. A few observations: 000: 000407 000606 000000 000000 000000 000000 000000 000001 An a.out header, with the 0407 'magic' here performing its original intended function - to branch past the header. 314: 105737 177560 002375 Some console I/O stuff - this two instruction loop waits for the input ready bit to be set. 326: 042700 177600 020027 000101 103405 020027 000132 101002 More character processing - the first instruction clears the high bits of R0, and the next two sets of two instructions compare the contents with two characters (0101 and 0132), and branch. 444: 000207 005000 021027 000407 001004 016020 460: 000020 020006 103774 012746 137000 005007 This seems like the code that checks to see if the thing is an a.out file (note the 'cmp *r0, $0407'), but the code is different from that code in mboot.s; in that, the instruction before the 'clr r0' (at 0446 here) is a 'jsr', whereas in this it's an 'rts pc'. And the code after the 'cmp r0, sp' and branch is different too. I love the '05007' - not very often you see _that_ instruction! 502: 012700 177350 012701 177342 012711 000003 105711 Clearly the code at 'taper:' (TC11 version). Noel

7 years, 9 months

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TUHS