4 ms·

For the transformer option: https://en.wikipedia.org/wiki/Transformer_read-only_storage https://en.wikipedia.org/wiki/Transformer_read-only_storage You can get

For the transformer option: https://en.wikipedia.org/wiki/Transformer_read-only_storage https://en.wikipedia.org/wiki/Transformer_read-only_storage You can get to the patent from here. The way I understand it, depending how/where the mylar sheet is punched or not (figure 8 is the unpunched sheet, figure 9/10 show a punched one) you will interrupt some of the connections and that particular line (the primary) will pass outside or inside the transformer core, so the secondary will be energized or not (1/0 output). By changing the mylar sheets you can "reprogram" the microcode ROM. I'm not an electrical engineer, so my terminology might not be 100% correct :) More on this: https://www.quora.com/How-was-the-IBM-System-360-microcode-loaded-into-a-machine https://www.quora.com/How-was-the-IBM-System-360-microcode-l... https://en.wikipedia.org/wiki/IBM_System/360_Model_30#Microcode https://en.wikipedia.org/wiki/IBM_System/360_Model_30#Microc... https://preview.tinyurl.com/ibm360mylar https://preview.tinyurl.com/ibm360mylar

kens 8y ago
That's a good explanation of the transformer read-only storage (TROS) used by the Model 20 and Model 40. Microcode storage gets even more complicated, as IBM use different microcode storage techniques on different 360 models, for a combination of technical and political reasons. The fundamental problem was how to implement tens of kilobytes of ROM in a way that was affordable and could be updated in the field. The Model 30 used CCROS (Card Capacitor Read-Only Store). Like TROS, this used a mylar sheet with holes punched in it. However, in this case, the holes were capacitively sensed; an air compressor forced the sense lines against the card. The card was the same size as a punch card, so you could punch new microcode with a keypunch. The Model 50 and Model 65 used BCROS (Balanced Capacitor Read Only Storage). This was kind of like CCROS, but faster. It used 8 inch by 18 inch mylar sheets with an etched copper pattern like a PCB. Each sheet held 35,200 bits and the system used 16 sheets. The Model 25 stored microcode in the regular core memory, a rather boring solution. For faster performance, the high-end System/360 machines had hardwired control rather than microcode.
- gattilorenz 8y ago
  Wow, thanks for the extensive overview. It blows my mind thinking there was an air compressor to push sheets over the sense lines. I can't imagine how loud/full of different types of noise the mainframe as a whole was...

kens 8y ago

That's a good explanation of the transformer read-only storage (TROS) used by the Model 20 and Model 40. Microcode storage gets even more complicated, as IBM use different microcode storage techniques on different 360 models, for a combination of technical and political reasons. The fundamental problem was how to implement tens of kilobytes of ROM in a way that was affordable and could be updated in the field. The Model 30 used CCROS (Card Capacitor Read-Only Store). Like TROS, this used a mylar sheet with holes punched in it. However, in this case, the holes were capacitively sensed; an air compressor forced the sense lines against the card. The card was the same size as a punch card, so you could punch new microcode with a keypunch. The Model 50 and Model 65 used BCROS (Balanced Capacitor Read Only Storage). This was kind of like CCROS, but faster. It used 8 inch by 18 inch mylar sheets with an etched copper pattern like a PCB. Each sheet held 35,200 bits and the system used 16 sheets. The Model 25 stored microcode in the regular core memory, a rather boring solution. For faster performance, the high-end System/360 machines had hardwired control rather than microcode.

gattilorenz 8y ago
Wow, thanks for the extensive overview. It blows my mind thinking there was an air compressor to push sheets over the sense lines. I can't imagine how loud/full of different types of noise the mainframe as a whole was...