The following message is a courtesy copy of an article that has been posted to alt.folklore.computers as well.
[EMAIL PROTECTED] (Van Dalsen, Herbie) writes: > Someone wants to create a shared block of memory CSA/not and share it > between programs. My understanding is that a 24-bit program can > address 24-bit addresses, 31-bit...., 64-bit... So in my inexperienced > mind the 24bit program could never share in the happiness of this > above the bar heaven of shared storage. as i mentioned in this post http://www.garlic.com/~lynn/2007r.html#62 CSA 'above the bar' ... the way that i originally did sharing implementation and mmap support http://www.garlic.com/~lynn/subtopic.html#mmap was that the same shared object wasn't required to occupy the same virtual address in every virtual address space. however, it could represent a challenge when program images with "relocatable address constants" were involved http://www.garlic.com/~lynn/subtopic.html#adcon there would still be an issue of the amount of happiness (available in 24bit mode) as opposed to any happiness. it would create a problem for processors that had virtual caches ... i.e. cache lines indexed by virtual address ... resulting in synonyms/duplicates in the cache when the same object was addressed by different virtual addresses. here is old email discussing dual index 3090 D-cache http://www.garlic.com/~lynn/2003j.html#email831118 in this post http://www.garlic.com/~lynn/2003j.html#42 Flash 10208 other posts about virtual cache http://www.garlic.com/~lynn/2006u.html#37 To RISC or not to RISC http://www.garlic.com/~lynn/2006v.html#6 Reasons for the big paradigm switch http://www.garlic.com/~lynn/2006w.html#17 Cache, TLB, and OS one of the other issues for TLB (hardware that translates virtual page addresses to real page addresses) ... all the entries were tagged/associated with specific virtual address spaces ... i.e. "STO-associative". This generalized mechanism resulted in a huge number of "duplicated" entries CSA/common-segment. So as a special case optimization for the whole MVS CSA/common-segment hack gorp ... a special option was provided that identified virtual addresses as something belonging to common-segment. These areas then became associated in the TLB with effectively a system-wide, unique, artificial "common-segment" virtual address space (effectively violating the whole generalized virtual address space architecture ... rather than associated with generalized virtual address space ... it became associated with a custom operating system specific construct that was known to have very specific characteristics). past post in this thread discussing rise of the whole ugly common segment gorp http://www.garlic.com/~lynn/2007r.html#56 CSA 'above the bar' other posts in this thread http://www.garlic.com/~lynn/2007r.html#64 CSA 'above the bar' http://www.garlic.com/~lynn/2007r.html#65 CSA 'above the bar' ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [EMAIL PROTECTED] with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html
