Editing IBM System/370 (section)

===Subsequent enhancements===
Later architectural changes primarily involved expansions in memory (central storage) &ndash; both physical memory and virtual [[address space]] &ndash; to enable larger workloads and meet client demands for more storage. This was the inevitable trend as [[Moore's Law]] eroded the unit cost of memory. As with all IBM mainframe development, preserving [[backward compatibility]] was paramount.{{citation needed|date=October 2009}}

* Operating system specific assist, Extended Control Program Support (ECPS). extended facility and extension features for OS/VS1, MVS{{efn|One of these{{sfn|S370-MVS}} is required for MVS/SE and MVS/SP
* System/370 extended facility
* ECPS:MVS
* 3033 extension feature
}} and VM.{{efn|VM/370 R2, VM/BSE, VM/SE and VM/SP exploit  Virtual-Machine Assist and Shadow-Table-Bypass Assist{{sfn|S370-VM}} if they are available.
}} Exploiting levels of these operating systems, e.g., MVS/System Extensions (MVS/SE), reduce path length for some frequent functions.

* The Dual Address Space<ref name="dual-address-space-share-paper">{{cite conference
 | title = Dual Address Space & Linkage-Stack Architecture
 | id = Session 10446
 | author = Dan Greiner
 | date = 12 March 2012
 | conference = SHARE 118 Atlanta
 | url = https://share.confex.com/share/118/webprogram/Session10446.html
 | conference-url = https://share.confex.com/share/118/webprogram/
 | archive-url = https://web.archive.org/web/20210114021953/https://share.confex.com/share/118/webprogram/Session10446.html
 | archive-date = 2021-01-14
 | url-status = live
 }}
</ref> (DAS) facility allows a privileged program to move data between two address spaces without the overhead of allocating a buffer in common storage, moving the data to the buffer, scheduling an SRB in the target address space, moving the data to their final destination and freeing the buffer. IBM introduced DAS in 1981 for the [[IBM 303X#IBM 3033|3033]], but later made it available for some 43xx,<ref>{{cite book
 | title = A Guide to the IBM 4381 Processor
 | id = GC20·2021·2
 | date = April 1986
 | edition = Third
 | page = 128
 | section = Section 80: Comparison Table of Hardware - 4341 Model Group 12 and 4381 Processors
 | section-url = http://bitsavers.org/pdf/ibm/4381/GC20-2021-2_A_Guide_to_the_IBM_4381_Processor_Apr1986.pdf#page=137
 | url = http://bitsavers.org/pdf/ibm/4381/GC20-2021-2_A_Guide_to_the_IBM_4381_Processor_Apr1986.pdf
 | publisher = IBM
 }}
</ref> 3031 and 3032 processors. MVS/System Product (MVS/SP) Version 1 exploited DAS if it was available.
* In October 1981, the 3033 and [[IBM 308X#IBM 3081|3081]] processors added "extended real addressing", which allowed 26-bit addressing for physical storage (but still imposed a 24-bit limit for any individual address space). This capability appeared later on other systems, such as the 4381 and 3090.{{sfn|S370|loc=[http://bitsavers.org/pdf/ibm/370/princOps/GA22-7000-10_370_Principles_of_Operation_Sep87.pdf#page=28 Storage Addressing with Extended Address Fields]|pp=3{{hyp}}3}}
* The System/370 Extended Architecture ([[S/370-XA]]), first available in early 1983 on the 3081 and 3083 processors, provided a number of major enhancements, including expansion of virtual address spaces from [[24-bit computing|24-bit]]s to [[31-bit computing|31-bit]]s, expansion of real addresses from 24 or 26 bits to 31 bits, and a complete redesign of the I/O architecture.
* In February 1988, IBM announced the Enterprise Systems Architecture/370 ([[ESA/370]]) for enhanced ('''E''') 3090 and 4381 models. It added sixteen 32-bit [[access register]]s, more addressing modes, and various facilities for working with multiple address spaces simultaneously.
* On September 5, 1990, IBM announced the Enterprise Systems Architecture/390<ref name=MK.390>{{cite web
 | url         = https://www.ibm.com/ibm/history/exhibits/mainframe/mainframe_PR390.html
 | title       = System/390 Announcement
 | website     = IBM Archives
 | date        = 23 January 2003
 | publisher   = IBM
 | access-date = 2017-01-29
 | archive-url = https://web.archive.org/web/20231026082859/https://www.ibm.com/ibm/history/exhibits/mainframe/mainframe_PR390.html
 | archive-date = 2023-10-26
 | url-status  = dead
 }}
</ref> ([[ESA/390]]), upward compatible with ESA/370.