The zSeries is based on the z/Architecture™, which is designed to reduce bottlenecks associated with the lack of addressable memory and automatically directs resources to priority work through Intelligent Resource Director. The z/Architecture is a 64-bit superset of ESA/390.
z/Architecture is implemented on the z990 to allow full
64-bit real and virtual storage support. A maximum 256 GB of real storage is available on z990 servers. z990 can defi ne any LPAR as having 31-bit or 64-bit addressability.
z/Architecture has:
•64-bit general registers.
•New 64-bit integer instructions. Most ESA/390 architec- ture instructions with 32-bit operands have new 64-bit and 32- to 64-bit analogs.
•64-bit addressing is supported for both operands and instructions for both real addressing and virtual addressing.
•64-bit address generation. z/Architecture provides 64-bit virtual addressing in an address space, and 64-bit real addressing.
•64-bit control registers. z/Architecture control registers can specify regions, segments, or can force virtual addresses to be treated as real addresses.
•The prefi x area is expanded from 4K to 8K bytes.
•New instructions provide quad-word storage consistency.
•The 64-bit I/O architecture allows CCW indirect data addressing to designate data addresses above 2 GB for both format-0 and format-1 CCWs.
•IEEE Floating Point architecture adds twelve new instruc- tions for 64-bit integer conversion.
•The 64-bit SIE architecture allows a z/Architecture server to support both ESA/390 (31-bit) and z/Architecture (64-bit) guests. Zone Relocation is expanded to 64-bit for LPAR and z/VM®.
•64-bit operands and general registers are used for all Cryptographic instructions
•The implementation of 64-bit z/Architecture can help reduce problems associated with lack of addressable memory by making the addressing capability virtually unlimited (16 Exabytes).
z/Architecture Operating System Support
The z/Architecture is a tri-modal architecture capable of executing in 24-bit, 31-bit, or 64-bit addressing modes. Operating systems and middleware products have been modifi ed to exploit the new capabilities of the z/Architecture. Immediate benefi t can be realized by the elimination of the overhead of Central Storage to Expanded Storage page movement and the relief provided for those constrained by the 2 GB real storage limit of ESA/390. Application programs can run unmodifi ed on the zSeries family of servers.
Expanded Storage (ES) is still supported for operating sys- tems running in ESA/390 mode (31-bit). For z/Architecture mode (64-bit), ES is supported by z/VM. ES is not supported by z/OS in z/Architecture mode.
Although z/OS does not support Expanded Storage when running under the new architecture, all of the Hiperspace™ and VIO APIs, as well as the Move Page (MVPG) instruc- tion, continue to operate in a compatible manner. There is no need to change products that use Hiperspaces.
Some of the exploiters of z/Architecture for z/OS include:
•DB2 Universal Database™ Server for z/OS
•IMS™
•Virtual Storage Access Method (VSAM)
•Remote Dual Copy (XRC)
•Tape and DASD access method