Questions tagged [pdp-11]
For questions regarding the DEC PDP-11 minicomputer.
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How were Western computer chips reverse-engineered in USSR?
The British ZX Spectrum computer had many clones in the Eastern Bloc. It seems many of them were built using Russian-made chips from the Angstrem factory in Zelenograd in/near Moscow. The Russian ...
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Why were the /\ (min) and the \/ (max) operators abandoned in the C language?
In the UNIX V7 version of the C language (but not yet in the V6 version), there were the /\ (min) and the \/ (max) operators. In the source of the scanner part of the compiler,
case BSLASH:
if (...
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Why did the PDP-11 include a JMP instruction?
The PDP-11's program counter was addressable in two ways: as a general purpose register or as a memory location.
Still, the PDP-11's instruction set included separate instructions for moving a new ...
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What motivated the weird boolean instruction repertoire of the PDP-11?
The PDP-11 has seven dyadic instructions (I'm not counting the byte/word varieties separately), which take a full six bits for each of its operands. That's twelve bits to specify the operands, and ...
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Were there any LSI-11 like home computers outside of Russia?
In my childhood I had one of these:
https://en.wikipedia.org/wiki/Electronika_BK
Note, that the CPU of this is based on LSI-11. This is rather surprising because PDP-11 took a room (I was lucky ...
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PDP-11 instruction set inconsistencies
The wiki page PDP-11 architecture has a cryptic paragraph with no references or examples:
Inconsistent instructions
Over the life of the PDP-11, subtle differences arose in the implementation of ...
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Why was Logo created?
The Logo programming language was created by researchers at MIT's AI Lab. Its post-1980s use has been predominately in the educational field, but is this what the language was originally designed for?
...
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Was the MC6800 a PDP-11 or PDP-8?
According to Gordon Bell, the 6800 was based on the PDP-11. According to Chuck Peddle, it was a PDP-8.
Can anyone with knowledge of the PDP's pass judgement?
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May the PDP-11's stack grow in either direction?
According to this answer, the stack grows downward. It's in §4.4 of the cited document:
As another example, the DEC PDP11 range has a hardware
stack which grows with decreasing store addresses....
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Why does AT&T syntax use * and $?
In a comment to an answer about AT&T assembly syntax, another-dave asked the following:
DEC used #foo for an immediate operand in -11 assemblers; the Unix guys apparently preferred $foo, which ...
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Trying to understand some assembly syntax in the Unix v7 write system call
so here is the code: (which comes from here, I've also verified this source is in my unix v7 distribution). For reference, this is running on a PDP-11 simulated with the simh program (so please keep ...
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PDP-11 Program to Execute Only in the Registers
The contents of processor registers of a PDP-11/05, etc were available at UNIBUS memory addresses and it was possible to execute a small test program just in the processor registers without accessing ...
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What is the history of the PDP-11 MARK instruction?
The PDP-11 MARK instruction was intended to be used as part of the standard PDP-11 subroutine return convention. MARK facilitated the stack clean up procedures involved in subroutine exit.
To use it, ...
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14
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1
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"MOS" - Mini Operating System for PDP-11?
Around 1977 or so, I worked with MOS, a "mini" operating system for the PDP-11. I think it was originally developed at SRI, to support the BBN Packet Radio networking research. It was ...
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How did 2-chip CPUs work?
The 1970s saw a big transition from CPUs built from thousands of discrete components, to CPUs implemented on a single chip, with the occasional use of bit-slice components along the way.
There were, ...
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Does the in-code argument passing conventions used on PDP-11's have a name?
Some subroutine calls on PDP-11 machines would be coded with the arguments appearing immediately after JSR or EMT instruction, something like this (apologies for not knowing the exact MACRO syntax):
...
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PDP-11/34 bit 8 in MMR0: maintenance mode - what does it do?
While attempting to write a PDP-11/34 emulator, I noticed that there's a bit called "maintenance" in the MMR0 (SSR0) register (the 8th).
What does it do?
In the manual I read:
Maintenance/...
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1
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Typical academic PDP-11 configuration for emulation
What was the typical configuration — CPU, memory, disks (number and type), printers, terminals, OS, etc — for a university PDP-11 system in the mid-late 1970s? I'm more interested in the FORTRAN/BASIC ...
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Can PDP-11 general registers be referenced by memory addresses?
From time to time it is mentioned in RC that the PDP-11 general registers R0-R7 are accessible at addresses 177700 to 177717 (considered as 16 bit program addresses).
The mapping is as follows, again ...
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12
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On-disk structures for Files-11 format (RSX11)
I'm looking for an explanation, or a link to documentation of the on-disk structures of the Files-11 format, that is, the format of disks used by RSX-11 on the PDP-11. Also known as ODS-1, the ...
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What is the difference (if any) between these two expressions in FOCAL?
I am trying to understand the 1969 FOCAL program Hamurabi in detail. The program was originally written for the PDP-8 version of FOCAL, but I am running it on the BK 0010-01 which presumably is a ...
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Was the PDP-11 coroutine instruction actually used?
In a typical description of the coroutine mechanism it usually mentioned that the PDP-11 instruction set provided a way to effect the coroutine switch by a single instruction, namely
JSR PC,@(SP)+.
...
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What causes the monitor to reduce to four lines on BK 0010 Focal?
When working with the Focal cartridge inserted on my BK 0010, the area displayed on the monitor suddenly reduces to just four lines
, instead of the usual 20
Each time this has happened when I've ...
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Was it really possible for a PDP-11 to address more than 32K words memory without an MMU?
In an answer by user RichF, it is claimed that the previous-address-space moves were able to access 'all of memory' without memory management being enabled.
The instructions MFPI (move from previous ...
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2
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How to view register contents on the PDP-11 console?
I have a PiDP-11 kit, which emulates a PDP-11/70 console. I've been using it as a launch point to gradual learning about the original machines and so far have been able to read/write memory and launch ...
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Were any PDP-11 systems with Corita Kent side-panels actually sold?
Somewhere around 1980, I heard about PDP-11 systems that had side-panels designed by Corita Kent (a nun and pop artist, who amongst other things designed a stamp for the US post office, and gas ...
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Timing and microcode in the PDP-11/40
I've been trying to figure out how the sequence of microcode instructions as described in the [schematics and ROM listing][1] in the PDP-11/40 (KD11-A Processor) relates to the timings given in ...
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How many bits are stored in a memory location in a PDP-11?
PDP-11 is said to be word addressable, which means every data access returns 16-bit data. Suppose I give a read request for address 100 in memory. Will it return 8 bits (LSB) from address 100 and ...
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Was the design of the PDP-11 Floating Point Processor responsible for C's willingness to do arithmetic on floats at double precision?
The Wikipedia page on PDP-11 architecture has a very interesting bullet point in the section on the Floating Point Processor extension to the basic architecture:
full floating point operations on ...
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What was the clock speed and ips for the original PDP-11?
What was the clock speed of the first generation of the PDP-11 with the KA11 cpu? This sounds like something that should be easily googlable but so far I have found nothing. I'm also interested in ...
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Is there anything special about /dev/console?
I am using the SimH emulator to emulate a PDP-11 computer with UNIX V7 installed on it. So basically I am emulating something like this:
I issued the tty command to see on which TTY port my terminal ...
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simh skipping parts of the v5 unix boot process?
I tried to run v5root.gz on simh V3.8 (unix research version 5). This works insofar as I get a login prompt.
If I though look at the source code of main.c (line 55) of the kernel in that image, then ...
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Is the SimH emulator available on macOS?
Is the SimH emulator available for macOS? I can't find it on their website: http://simh.trailing-edge.com/
What I am specifically interested in is to run UNIX V7 on a PDP-11 emulator.
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How do I make a Unibus device?
The Unibus was an innovative I/O system used by DEC PDP-11 machines. A device would choose some memory addresses to respond to, register an interrupt vector, then communicate with software that was ...
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Creating a PDP-11 bootable disk
I want to create my own boot disk (an image file to use with simh) from my own PDP-11 code but I don't know how the code needs to be written to the disk/file so that it boots. I can load my code using ...
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How were terminals connected to a PDP-11 computer?
This is how I think terminals were connected to a PDP-11 computer:
A PDP-11 computer had only one port that you can connect the console terminal (/dev/console) to, and if you want to connect more ...
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PDP 11/70: how does MTPI work?
I'm trying to understand the MTPI (and its MFPI counterpart) instruction on the PDP/11.
As far as I understood, it:
it retrieves a value from the "current" memory space with the current ...
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What was the most popular operating system on the PDP-11 computers?
What was the most popular operating system on the PDP-11 computers?
And is it known what percentage of PDP-11 computers used this operating system?
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'Trap stack push abort' on the PDP-11 with SIMH
I'm trying to run a bare-metal example program from the DL11 manual that echoes user input. When I try to run it via SIMH however I get a 'Trap stack push abort' error when it tries to access address ...
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What was a DEC PDP-11/85 intended to be, and why might it be able to use DECsystem-10 software?
In this DEC PDP-11 Strategy Memo from Sept 1974, there is this curious question.
HOW MUCH OF THE DEC SYSTEM 10 SOFTWARE
CAN THE 11/85 USE, OR DOES THE 11/85 HAVE
TO START FROM SCRATCH?
CONFLICTING ...
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What’s the most advanced os I can run on a non memory management pdp11 (ie 11/20)
Building my own emulator. I only have the basic , no memory management, model going (11/20?). I started with caps11. What’s my best choice for a disk based os.
EDIT: and of course if anybody has the ...
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Could we change the baud rate for the two serial ports on a terminal and on a computer?
Say we have a terminal (for example: VT100) that is connected to a computer (for example: PDP-11), and UNIX V7 is installed on the computer.
The terminal will have a serial port that is connected ...
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How MOVB, TSTB and all byte instructions works in odd address read in PDP11?
I'm writing a PDP11 emulator. When CPU read odd address on Unibus odd address exception is launched. But the code below INC increments PRTPTR by 1 which make TSTB @PRTPTR generate a exception when it ...
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What was the DEC CR11 card reader 'compressed Hollerith code' for?
In this manual for the DEC CR11 card reader controller, the controller can deliver the card content to the PDP11 in either of two forms:
Column binary: the 12 rows of hole/no-hole are delivered in ...
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When did an overlay linker first appear in a PDP-11 UNIX OS?
On a 16-bit system with at most 64K of RAM available for a user program, one would think of having an executable overlay mechanism as an indispensable tool to maximize the amount of memory available ...
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Does anybody have the PDP-11 CAPS-11 source code?
CAPS-11 is the Casette Programming System for the PDP-11. The manual is available at Bitsavers, binaries can be found at SimH.
The manual contains instructions how to assemble the system from source, ...
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PDP-11 CIS MOVTC instruction... does what?
I'm looking over the PDP-11 CIS instruction set. Here is the listed description of the MOVTC (and MOVTCI) instruction:
MOVTC(I): Move translated character
A longer description can be found in the ...
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3
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3
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The baud rate of which serial card does the "stty" command returns in UNIX V7?
I am using a PDP-11 emulator with UNIX V7 installed on it.
The stty command returns the baud rate:
To which serial card does this returned baud rate belongs to, is it the terminal serial card, or ...
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2
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How to implement a 'write' function in pdp-11 / MACRO-11 / ODT using simh?
So, I'm working on a project where I'm aiming to get the first winner of the IOCCC (obfuscated c code contest) dissected down to the last detail... The program is mullender.c which you can find by ...
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PDP-11 ASH instruction: who is right?
I'm trying to figure out why emulation of the ASH instruction by my emulator is marked as faulty.
I use the XXDP+ "EKBBF0" test to verify its cpu emulation.
If I look at the source-code of ...