XR over SR seems to be a persistent myth. I have been told again and again from time to time that XR was faster than SR. There is no reason it should be, and the evidence is that it is not.
Charles -----Original Message----- From: IBM Mainframe Discussion List [mailto:[email protected]] On Behalf Of glen herrmannsfeldt Sent: Monday, June 02, 2014 5:51 PM To: [email protected] Subject: XR vs SR Robin wrote: > XR Rn,Rn is faster than SR. > But does it matter? Who says that XR is faster than SR? I know the IBM OS/360 software and compilers generate SR instead of XR. From: http://bitsavers.trailing-edge.com/pdf/ibm/360/A22_6825-1_360instrTiming.pdf on many S/360 models SR was much faster than XR, equal on the 2040, and not slower on any. Do you have any timings for high-end S/370 or later models? (With instruction overlap, it is pretty much impossible to give single instruction timings on many models.) Since IBM software assumes SR is faster, they would have a reason to special-case it on any later models, but maybe not XR. -- glen ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
