Rope Memory
I was watching a program today on the Science Channel called “Moon Machines – The Navigation Computer.” This is a six part series that reviews the history of the development of the systems required to complete the Apollo mission to the moon. This particular episode was on the development of the Navigation Computer used in the command module and the landing computer used in the Lunar Lander. This was in the late sixties and computers were not what they are today. The navigation computer has about 72Kbytes for program storage. The software was being developed at the MIT Instrument Lab. To store the program in the Navigation Computer they used Rope Memory. This is a version of Core Memory technology that can be used as a Read Only Memory to store programs. I had never heard of Rope Memory and I have been around computers for a very long time!
By weaving the sense wires through or around the cores of the memory they can hardware the program into the computers memory system. Here are a couple of photos of the Rope Memory.
A Rope Memory board having a program “threaded” into the memory.
A Rope Memory wired with a program.
At least one commercial computer used a Rope memory for its control store. The Modcomp III, designed in 1970, released 1971, used a 256x40bit read-only memory. This memory contained the microcode for the machine, a 16kx16 bit binary processor with a 5 MHz clock.
The “rope” threaded through each of the magnetic toroids in either a positive or negative sense, rather than a hit/skip method for sensing a 1 or 0.
The program was fixed, because the rope was woven through an array of toroids, rather than an open-core style of magnetics. The inconsistent air gap of a U-I core caused s/n problems over the operating temperature range.
A successor to this computer, with custom microcode, ran the ground checkout sequence for the Saturn 5 launches of the Apollo program.
“Those were the days, my friend”
OMG, the Modcomp III !! I did not know that was how the microcode was loaded in the Modcomp.
My second job was with a company in Ft. Lauderdate, Computer Products, Inc. CPI was 30 people in an old Rexall Drugs on Dixie Highway in Ft. Lauderdate. The startup company, Modular Computer Systems moved in to the old drug store CPI moved out of in early 1970.
A year or so later, Modcomp built a building in Pompano Beach in the same industrial complex where CPI was (Gateway). Did you work for Modcomp? If so, could have seen you at “The Circus” or at “Big Daddy’s!”
I worked for CPI for 23 years. It was a great time back then, three computer companies in Ft. Lauderdale / Pompano Beach. SEL, Datacraft / Harris, and Modcomp. CPI did data acquisition systems specializing in low level analog signal processing.