Transporting an LGP-30

william degnan billdegnan at
Mon Dec 26 10:43:08 CST 2016

On Mon, Dec 26, 2016 at 11:01 AM, Christian Corti <
cc at> wrote:

> On Sat, 24 Dec 2016, william degnan wrote:
>> Here are my notes on the LGP 30
> There are several errors in those notes:
You addressed me publicly so I will reply publicly.  Several "errors" might
be a few clicks too harsh given a person can get the idea of what I clearly
meant AND I was referring to simH, trying to figure out how to make the
simH of the LGP-30 work.  I don't have an actual machine and don't claim to
be an expert in its use, not the Flexowriter...have a spare?

> - "The basic (hardware) bootstrap in LGP-30 mnemonic format:"
> There is no hardware bootstrap.
I put hardware in parens for a reason.  For me its a way to communicate the
"level" of the bootstrap I could not think of a better way at the time to
describe how it works in *simH*, which is what I was writing about in my
post titled "SIMH Emulator - 1956 LGP-30 Computer".

> - The addresses in the bootstrap loader (program 9.0) must be hexadecimal
> and the bootstrap is entred as follows:
> C3W00 - P0000
> C3W04 - I0000
> C3W08 - C3W14
> C3W0J - P0000
> C3W10 - I0000
> U3W00
Thanks, good to know.  I was writing from a SIMH standpoint, not the actual

> - "4-character binary equivalent of the flexowriter single-character ascii
> commands"
> Ehm, ASCII wasn't "invented" at that time. There are no Flexowriter
> commands, the Flexowriter code is the LGP-30 code.

Yes, but the Flexowriter encoding is not the same as ascii, but ascii is a
common format someone today can relate to and convert from.    One can
translate Flexo encoding into ascii and you need to be able to do this to
effectively use SIMH if you don't have a Flexowriter.

> - "First "B4627" is converted into binary-coded decimal format and entered
> into the accumulator"
> There's no conversion, the character code of the Flexowriter *is* the
> binary code of the LGP-30.
OK.  I converted in my head to understand it logically while using SIMH,
 This is a necessary step if you want to try to load in a bootstrap into
the simH drum, etc.

> - "The accumulator is actually 64 separate 32-bit accumulators (one for
> each drum track), same value on each copy."
> ???

Yes but you know what I mean, I am working in a vacuum teaching myself, I
could have been more precise, but that's how I understood it at the time I
wrote what I wrote.

> The accumulator is one track with 32 double-width (i.e. 64 bits) sectors.
> You need the long accumulator when multiplying two 31-bit numbers (you
> can't store a 32 bit number to the memory because the LSB is always 0)
> All the registers are circulating registers meaning that the contents is
> read and immediately written back to ensure that it is accessible at any
> word (sector) time.
> Everything you need to know about the architecture and programming of the
> machine can be found in the manuals BTW (including schematics, flow charts,
> instruction description etc.). The manuals are online since many many years.
> Christian

I have all of the manuals.  Basically I sat down at a simH prompt and the
manuals and tried with only that to make sense of the LGP-30.  I take it
you have a machine at  your disposal, I wish I did too.  Thanks for sharing
your knowledge, I will update my web site to make it more accurate.


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