decimal computing

Lee Courtney lcourtney at
Tue Mar 15 12:05:40 CST 2005

Sorry, minor nit...

> In the 1620, the memory is a separate cabinet, connected bycables
> to the CPU cabinet.

The first 20K characters of memory resided in the CPU cabinet, up to 40K
characters of optional add-on memory resided in the external cabinet.


Lee Courtney
CHM 1620 Restoration Team Member

> -----Original Message-----
> From: cctalk-bounces at
> [mailto:cctalk-bounces at]On Behalf Of woodelf
> Sent: Tuesday, March 15, 2005 8:21 AM
> To: General at; Discussion at and Off-Topic
> Posts
> Subject: decimal computing
>  >That depends on whether you trust the datapath between the memory and
>  >the CPU. In the 1620, the memory is a separate cabinet,
> connected bycables
>  > to the CPU cabinet. A wise designer would run parity on that
> interconnect.
>  >That's still true: high end "system on a chip" designs have ECC memory
>  > AND parity (at least) on the buses -- even if they only run inside
> the chip.
>  > I don't actually know if there was parity there. Probably yes, since
>  > As for sign bit per digit, in the 1620 the "sign" bit serves two
>  > purposes -- on the least significant digit it's the sign of the
>  >number, on the most significant digit it's the "this is the last
>  >digit" marker.Not that the 1620 is all that efficient -- at 12
> digits per
> >instruction, code density was pretty low.
> I don't think that the code density was that bad since it was a two
> address instruction.
> If you consider at the time most computers had the power of a 4 function
> calculator
> with tiny amount of data memory the base machine with 20,000 digit memory
> was a lot of memory. What was real inefficient was converting from
> internal codes
> to external coding like printers, paper tape, punch cards all with
> different formats.
> (I don't have one, I just read the book about it)

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