memory map for RT-11 v 5

Don North north at
Sun Jul 24 16:29:59 CDT 2016

On 7/24/2016 8:06 AM, william degnan wrote:
> On Jul 24, 2016 8:58 AM, "Jerome H. Fine" <jhfinedp3k at> wrote:
>>> On Wednesday, July 20th, 2016 at 18:02:44 - 0400, william degnan wrote:
>>> Is there a minimum memory requirement for RT-11 v5?  I was discussing
> with
>>> Ray Fantini about it today, unsure...anyone know if 16K will work (from
>>> 000000).
>>> Bill
>> You need to be more specific!  Starting with V05.00 of RT-11 in 1983,
>> there were a total of 17 versions released up to V05.07 in 1998, including
>> sub-versions V05.01B, V05.01C, and V05.04A to V05.04G of RT-11.
>> Up until V05.05 of RT-11, RT11SJ.SYS required the least memory which
>> was replaced with RT11SB.SYS for V05.06 and V05.07 of RT-11.
>> Attempts to boot from RT11SJ.SYS under V05.00 of RT-11 with 24K
>> bytes of memory were successful.  Attempts to boot with 16K bytes of
>> memory were unsuccessful.  An RK05 was used as the disk drive since
>> it is close to the smallest device driver.  The answer to your question
>> about using 16K bytes of memory is NO for all versions of RT-11 starting with
>> V05.00 or RT-11.
>> Attempts to boot from RT11SJ.SYS under V04.00 of RT-11 with 24K
>> bytes of memory were successful.  Attempts to boot with 16K bytes of
>> memory were also successful.  An RK05 was used as the disk drive.  The
>> error message "Insufficient memory" is displayed, but some useful work
>> might be done with just 16K bytes of memory. However, you did not
>> ask if useful work being done was one of the criteria?
>> NOTE that I used the Ersatz-11 emulator to check the above details,
>> so there might be a difference with actual hardware.
>> If you have any more questions, please ask.
>> Jerome Fine
> Thanks for the details.  I had been trying to boot rt-11 v5.3 on a 16k core
> 11/40 using RL11 (rl02) and it did not work.   The system was unable to
> complete the initialization.  CPU diagnostics passed, I could load BASIC
> papertape.  RL11 working correctly.  In this context I posted my question.
> After I posted my message here I loaded up simh and emulated an 11 with
> 32k.  RT-11 v5.3 disk boots.  When I re-built the system and reduced to
> 16k, I could not boot, bombed.
> One thing to remember is 16KW in a pdp11 is not the same thing that simh
> refers to when one sets the CPU to 16K.  WWW do not all make this
> distinction clearly.  I get it, just making this comment for future readers
> of this thread.
> Bill

RT-11 v5.03 single job monitor boots fine and runs in just 32KB (16KW) of memory.

You need to be more specific about how you specify the memory configuration 
(words vs bytes).

DEC routinely specified everything in KW (words) but most users and tools use KB 
(bytes) nowadays.

Note that to force RT11SJ (vs RT11FB) to boot on the below image I booted first 
using FB
in a larger memory configuration, did a:


to force it to boot using the SJ monitor the next time.


PDP-11 simulator V4.0-0 Beta        git commit id: 4065f47f

CPU     11/34, FPP, idle disabled, autoconfiguration enabled

NOTE: ctrl-E to exit to SIMH monitor
sim> boot rl1

RT-11SJ (S) V05.03

.sho all

RT-11SJ (S) V05.03
Booted from DL1:RT11SJ

USR   is set SWAP
EXIT  is set SWAP
KMON  is set NOIND
TT    is set NOQUIET
SL    is set OFF
EDIT  is set KED
KMON nesting depth is 3

PDP 11/34 Processor
32KB of memory
FP11 Hardware Floating Point Unit
Extended Instruction Set (EIS)
Memory Management Unit
60 Cycle System Clock

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