On 15 October 2014 02:55, Elardus Engelbrecht <[email protected]> wrote: > Ok, After some RTFM in SMF book, POP, macros references, I believe it is > 26.04166 microseconds (one timer unit), which if you multiply it by 38400, > you arrive at 999 999.744 which could be translated to about 1 second AFAIK.
This particular magic number comes from the System/360 Interval Timer, which was the only timer on S/360, and persisted into S/370 architecture, but was dropped in 370/XA. It is a 32-bit signed fixed-point number, defined such that bit position 23 is decremented every 1/300 of a second. This was a convenient definition to implement in a basic form in both 50 and 60 Hz countries, since the rate is easily derived from the power supply. But in all but the most low end models, a bit position to the right of 23 was decremented at a faster rate, giving higher precision. Bit position 31 represents 13.020833... μS; I don't know why double that, or bit position 30, is considered a "timer unit" for SMF purposes. Possibly they wanted to be able to represent more than the 7.7ish hours that the positive number range of the architected format provides. Tony H. ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
