On 2/18/2014 3:26 AM, Elardus Engelbrecht wrote:
Ed Jaffe wrote:
To put into perspective, it took 13 cycles to access a doubleword operand on a
S/360 Model 91. That same memory access on a zEC12 can now be up to 75 TIMES
slower (relatively speaking).
Interesting. Did you measured that with a handheld tamperproof stopwatch? ;-D
;-D
Google is your friend. There are many S/360 references on the Internet.
This one: http://www.columbia.edu/cu/computinghistory/36091.html
confirms, "The Model 91 CPU cycle time (the time it takes to perform a
basic processing instruction) was 60 nanoseconds. Its memory cycle time
(the time it takes to fetch and store eight bytes of data in parallel)
was 780 nanoseconds." 780/60 = 13 cycles for memory access.
Does that '75 times slower' includes handling by CP cache or not (bypassed)?
Also, what 'access' are you implying? Fetch, Store or Update? Copy to/from
Register? Compare to something?
Most of that is non-sequitur. We've already established in prior
conversations that uncached memory access is approaching 1000 cycles on
modern System z machines. That's roughly 75 times slower (relatively
speaking) than memory access speed on the Model 91.
--
Edward E Jaffe
Phoenix Software International, Inc
831 Parkview Drive North
El Segundo, CA 90245
http://www.phoenixsoftware.com/
----------------------------------------------------------------------
For IBM-MAIN subscribe / signoff / archive access instructions,
send email to [email protected] with the message: INFO IBM-MAIN
