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101090 discussions

PDP-11 pages/segments/etc (Was: PDP-12 at the RICM)

by jnc＠mercury.lcs.mit.edu

> From: Johnny Billquist > While the pages are variable in length, each page starts at an 8K > virtual address boundary. Which is another difference between PDP-11 'pages', and real pages as used on every other machine of the period which had virtual memory: normally, page sizes were small, ranging from 512 bytes to 1K words. No other machine was even _close_ to 8KB. In other machines, the page was the fundamental unit of memory allocation; on PDP-11's, that unit is the click (0100 bytes). > If you only had one page, and that page covered the full virtual > address space, then I would agree that it was a segment model. That's only true in the brain-damaged x86 model, in which 'segments' were added as a kludge to expand the address space. If you study _real_ segmented architecture machines, like the GE645, NS32K, etc you will discover that in them, a segment is a fixed-size chunk of the total (much larger) address space, and they start at fixed offsets in that space. A segment which is less than full-sized leaves a gap in the address space before the (fixed) start of the next segment. All of which sounds just like the 'pages' in the PDP-11... Noel

10 years, 11 months

Front Panel Update

by rodsmallwood52＠btinternet.com

Hello Everybody In the course of doing the artwork for 8/e type B I have turned up some more variations. The list now looks like this: 1. Switch position markings 2. Line round switch area 3. The EMA title block isolated from the other titles 4. Lines between groups of three lamps 5. lab8/e instead of pdp8/e So far I can't find any reasons as to why these variations seem to be random. The only thing that is not cosmetic is the two types of switch position. I am minded to add all of variatons (excluding lab8/e) because they seem progressive: No line round the switch area becomes line round the switch area EMA title attached becomes EMA title detached No lines between lamps becomes lines between lamps Then produce two versions based on the switch position The issue is of course small batch costs. Comments gentlemen please Rod

10 years, 11 months

Seeking to buy / trade for a GRiD Compass 11xx to aid in silly project

by ian.finder＠gmail.com

Hi folks, I'm looking to buy at whatever price is fair a GRiD Compass (Not the DOS based ones) computer of any model-- and perhaps condition- as I may be able to repair I recently missed an ebay auction, which was sad. Let me know, Thanks, - Ian ----- Background. About a year or so, I purchased my first GRiD compass (1129) off another list member. I quickly gained two impressions: 1) The non MS-DOS based GRiD OS is really freakin' cool. 2) The documentation for these machines is nonexistent. I've recently acquired an 8086 ICE. My goal is to reverse engineer the machine and operating system to a reasonable degree, in order to glean enough information to enable the following tasks: 1) (High priority) Build a somewhat modern toolchain for GRiD OS 2) (This might be something I never get to) Build an emulator of the GRiD. Unfortunately, I don't want to- A) Have to leave my main machine taken apart, or constantly reassemble-disassemble it to attach it to the ICE. B) Develop for a system I have no spares for. Would love if someone who has an extra one of these they haven't used for a while would be willing to part with it or trade for it. In addition to whatever we work out, I'll toss in a free GRiDcase 3 to help with separation anxiety stemming from black magnesium computers. -- Ian Finder (206) 395-MIPS ian.finder at gmail.com

10 years, 11 months

STSC APL*PLUS System for VAX VMS User's & Reference Manual

by mark＠wickensonline.co.uk

Kind reader I have two manuals labelled STSC APL*PLUS System for VAX VMS: User's Manual and Reference Manual which were sent to me a number of years ago as paper copies - I now have the ability to easily scan these into PDF format. Would these be of interest to anyone? There is a PC version archived here http://www.math.uwaterloo.ca/apl_archives/apl/apl-plus/ that might benefit from the additional documentation. I've contacted Lee about this. I am interested if anyone has any history of this software (there are some general references out there about the STSC Mainframe and later PC versions) - and indeed if the software survived at all. Was VAX/VMS APL based on this version? Regards, Mark.

10 years, 11 months

Digital IDACS 11/07 Industrial PDP-11

by billdegnan＠gmail.com

I have an interesting brochure, that is not on bitsavers (that I can find), for the Digital " IDACS 11/07 Industrial Control System " This is a stand-alone-capable UNIBUS PDP 11 industrial system made for analog and digital inputs with RSX-11C software, FORTRAN, PDP-11 DOS, COMTEX-11. If this is something not well-known I can post a scan of the sales brochure. - Bill

10 years, 11 months

PDP-12 at the RICM

by jnc＠mercury.lcs.mit.edu

> From: Rich Alderson > Changing from PDP-8 operation to LINC operation was a matter of a > physical switch. Err, not according to the "Small Computer Handbook" (1967 Edition), which covers the LINC-8 in detail - at least, as I understand it? See, for instance, pg. 307 "A LINC HALT instruction will also stop the LINC and return control to the PDP-8." And see also the "Operational Summary", pp. 308-309, and Chapter 7, "LINC - PDP-8 Intercommunication". Reading the handbook, it _seems_ like, in theory at least, the two machines could run simultaneously (albeit contending for memory bandwidth), although the canonical programming approach was to have one pause while the other ran. Or perhaps that supposition is incorrect, and the two couldn't correctly deal with contention for memory (although the LINC used the standard PDP-8 'data break' mechanism for access to memory, which was used by DMA devices such as disks, so the -8 should have been able to deal with it; perhaps the LINC couldn't); or perhaps there was some vital piece of circuitry shared by both? I wonder if any LINC-8's still exist? > "PDP-8/i + LINC hybrid" The bone I have with that description (which may be technically correct) is that it implies that prior to the PDP-12, there were only the two separate machines (PDP-8 and LINC). But I know I'm a stickler for small details... :-) Noel

10 years, 11 months

68000 systems and paging.

by tsw-cc＠johana.com

There a re a couple of systems that used a 68000 in a Unix type environment.? I have worked on both.The first is an Altos ACS68000 system that used a 68000 and 4 (four, count'em) 68451 mmu units.? The way it did the memory allocation was to use "stack probes" to trip up a memory fault interrupt.? These probes were simple 'TST' instructions that indicated where the stack would grow to.? These instructions were easily "restarted" since they didn't change the register contents.? Subsequent instructions would have no memory faults and everything would be working nicely. The Rasio Shack Model 16 used the same system, but had a cruder MMU that had two offset and two limit registers.? The operating system was Xenix and worked OK, but the methods for memory management were not the best, but considering the hardware worked OK. The C compiler (from what I understand) was a precursor to GCC and had the stack probes code built in.? It was part of the activation record code. So, yes you can run a Unix style operating system on a 68000, you just need to be creative.? I don't know how others did it.? Yes, the 68010 (or later) was the solution to all the problems.

10 years, 11 months

PDP-12 at the RICM (Michael Thompson)

by michael.99.thompson＠gmail.com

> > Date: Mon, 13 Jul 2015 01:52:09 -0400 > From: "Kip Koon" <computerdoc at sc.rr.com> > Subject: RE: PDP-12 at the RICM > > Hi Michael, > I would be most interested in finding out more about this effort. Do you > have ongoing pictures documenting this effort? I'd love to have a PDP 8, > 11, 12 someday, but I don't have the space for something like that much > less the cost involved so I'll have to be satisfied with emulators on my PC > or eventually building one or more of these systems with current technology > like the SBC6120 if memory serves. Are there other possible alternatives? > I used a PDP-8/E in high school and college and have been quite interested > in the high capability PDPs like the PDP-11 Series for starters. I didn't > know there were PDP 12 Series computers. Are there other PDP series > computers as well? Congratulations on your restoration efforts! I wish I > could see what all you guys have been and are up to! Take care my friends. > > Kip Koon > computerdoc at sc.rr.com > http://www.cocopedia.com/wiki/index.php/Kip_Koon > Kip, I don't think that there is an emulator for the PDP-12 so you will need to find a real one. Details on the PDP-12 are here: http://www.ricomputermuseum.org/Home/equipment/dec-pdp-12 A running blog on the restoration is here: http://www.ricomputermuseum.org/Home/equipment/dec-pdp-12/dec-pdp-12-restor… Michael Thompson

10 years, 11 months

PDP-12 at the RICM (Michael Thompson)

by michael.99.thompson＠gmail.com

> > Date: Sun, 12 Jul 2015 16:10:10 -0500 > From: Jay Jaeger <cube1 at charter.net> > Subject: Re: PDP-12 at the RICM > > BTW, if there are particular cards you need / are bad, in addition to > the actual PDP-12, I have the backplanes and cards for a 2nd one, so if > you need something, we could probably work something out. > > JRJ > Jay, We will keep you in mind if we can't repair a flip-chip. -- Michael Thompson

10 years, 11 months

PDP-12 at the RICM

by jnc＠mercury.lcs.mit.edu

> From: Rich Alderson > PDP-12 12-bit word, PDP-8/i + LINC hybrid Err, DEC sold a PDP-8/LINC hybrid themselves (interesting machine, it's covered in one of the standard PDP-8 processor manuals), before the PDP-12 came out; the -12 was basically a re-engineered version of the 8/LINC. Noel

10 years, 11 months

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