Talk:IBM 1620 Model II

15cps?
"The console typewriter was replaced with a modified Selectric typewriter, which could type at 15 cps — a 50% improvement over the Model I."

Actually, I seem to remember it as 14.7cps -- can someone find out the truth? This relates to the communications channel, bits per char, baud rates, etc... Those were the days! 69.87.204.125 01:46, 17 September 2006 (UTC)


 * The figure 15cps came from Joe Crespo, the IBM engineer that designed the Selectric interface for the 1620. However he may have rounded the number to the nearest whole character.


 * The interface was parallel, one whole character at a time (not serial). On the Model I the typewriter interface took the 6 bit (and 1 parity bit) BCD character code and decoded it in relays to individual signals, one per key solenoid. The Selectric used with the Model II reduced this to 7 solenoids, driving the mechanical decoder internal to the standard Selectric that controlled the ball. Character timing in both the Model I and Model II was controlled by a motor driven cam assembly that switched microswitches on and off.


 * I have some original documentation on the Model II (but not schematics like I have on the Model I). If I get a chance I'll dig it out and see if it clarifies the detail (e.g., RPM of the timing cam assembly). -- RTC 19:29, 17 September 2006 (UTC)


 * OK, I looked it up: IBM Form # A26-5781-0 IBM 1620 Central Processing Unit, Model 2 on page 98 in the section on the Console Typewriter it lists both input and output speeds as 15.5 cps. I'll correct the article. -- RTC 07:48, 21 September 2006 (UTC)