question about how JPL handled double precision on IBM 7094 in the 60 Options

[ncc1701d]

Hello,
I have a question about they handled double precision floating point numbers at JPL in the 60s on the IBM 7094. First I give you a quote then ask the question.

John Strand: Author of the book Memoirs of an Astrophyscist Path to the Planets who worked at JPL in the 60s said the following on page 63

"The IBM 7040-7094 Direct Couple was the joing of two main frames. One computer handled
I/O and the other was principally for number crunching. The operating system was batch mode.
Double precision used two single precision floating-point words each with seperate characteristics and mantissas. I will never for forget this single precision augmentation because of the work necessary to unpack both words from the octal dump in order to find the decimal number. True double precsion with a single characteristic and mantissa would have to wait"....etc
Later in the book it says: "The IBM 360 had a single characteristic and mantissa for its double precision word." IBM 360 came right after the IBM 7094.

My question is if anyone knows about this method of combining 2 single precision words in order to make 1 double precision word? I am trying to read a binary file that may have used this method since the data was created on a IMB 7094 computer which came before the IBM 360. Nasa archives people say they dont have access anymore to orginal fortran programs that might give me some clues about my problem or the format and I have no way to get in touch with the books author so I am curious if anyone knows about this method?

this link here:
https://nssdc.gsfc.nasa.gov/nssdc/formats/I...4_7090_7094.htm
refers to 2 words that would make up a double precision floating point but it doesnt look like the "Second 36-bit Word" has its own characteristic AND mantissa or does it?
I am trying to reconsile what the auther said about his "I will never forget" comment about how he handled double precision and what my link says about how nasa handled double precision on the IBM 7094.
Any opinions, insights or info on this subject would be helpfull.
thanks

[nogal]

In the early 1970s I used the FORTRAN IV level F compiler first with the IBM 44-PS than with the DOS 26.2 operating system. Though, as mcaplinger says, there was not a string or character data type, we would do string manipulation using arrays of the LOGICAL type. Young students can be quite inventive... We did what we needed to do in order get the required results, using the tools at hand.

I no longer have the IBM language manual for FORTRAN IV but was able to locate my "A guide to Fortran IV programming" by Daniel D. McCracken.

Fernando

[JRehling]

This page, not specific to JPL, might be informative or interesting:

https://en.wikipedia.org/wiki/Single-precis...ormat:_binary32

23 bits allows for considerable precision in a significand (about 7 digits decimal). While spaceflight is an area where you never want any sources of failure, I'm curious when there was first the sense of need for more precision than that. 1960s engineering would not likely be able to operationalize sensors, actuators, etc., that could provide or require more precision than that, and with 1960s processors, the cost in speed would not be trivial. The question is, when would an iota of added precision be worth the halving of speed?

[mcaplinger]

23 bits allows for considerable precision in a significand (about 7 digits decimal).

Many numerical algorithms misbehave or even fail miserably in single precision. Double precision was added very early in the development of Fortran.