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Questions tagged [pdp-11]

For questions regarding the DEC PDP-11 minicomputer.

6
votes
2answers
780 views

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): ...
0
votes
3answers
186 views

PDP-11 JMP and JSR - how was the target specified?

As I understand it, the PDP-11 has a 16-bit address space with a fully loaded system having 28k words (56k bytes) after reserving some of the address space for I/O, which means if instructions must be ...
8
votes
1answer
199 views

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 ...
13
votes
1answer
410 views

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 ...
9
votes
5answers
1k views

PDP-11 stack may 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....
10
votes
2answers
660 views

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, ...
6
votes
1answer
363 views

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 ...
8
votes
1answer
386 views

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 ...
3
votes
3answers
219 views

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 ...
39
votes
2answers
22k views

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 (...
5
votes
2answers
251 views

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 ...
18
votes
3answers
844 views

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 ...
-5
votes
4answers
706 views

What is the starting address pointed by Stack Pointer in PDP 11?

To which memory location does the stack pointer point at the beginning of the program in PDP 11? And what can be the end address the SP can point to before overflow occurs?
7
votes
3answers
646 views

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 ...
9
votes
1answer
270 views

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 ...
8
votes
2answers
317 views

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 ...
7
votes
3answers
675 views

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.
10
votes
1answer
329 views

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 in the PDP-11/40 (KD11-A Processor) relates to the timings given in Appendix C ...
11
votes
2answers
616 views

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)+. ...
42
votes
2answers
5k views

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 ...
13
votes
1answer
301 views

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 ...
10
votes
1answer
351 views

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 ...
46
votes
8answers
5k views

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 ...
7
votes
1answer
226 views

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 ...