IBM Enterprise Systems Architecture

On February 15, 1988, IBM announced Enterprise Systems Architecture/370 (ESA/370) for 3090 enhanced ("E") models and for 4381 model groups 91E and 92E. In addition to the primary-space and secondary-space addressing modes that later System/370 models, and System/370 Extended Architecture (S/370-XA) models, support, ESA has an access register mode in which each use of general register 1–15 as a base register uses an associated access register to select an address space. In addition to the normal address spaces that machines with the dual-address-space facility support, ESA also allows data spaces, which contain no executable code. A machine may be divided into Logical Partitions (LPARs), each with its own virtual system memory so that multiple operating systems may run concurrently on one machine. ==ESA/390 architecture==

An important capability to form a Parallel Sysplex was added to the architecture in 1994. ESA/390 also extends the Sense ID command to provide additional information about a device, and additional device-dependent channel commands, the command codes for which are provided in the Sense ID information, to allow device description information to be fetched from a device. Starting with the System/390 G5, IBM introduced: • the basic floating-point extensions facility, which increases the number of floating-point registers from 4 (0, 2, 4, 6) to 16 (0–15); • the binary floating-point (BFP) extensions facility, which supports IEEE 754 binary floating-point numbers, with an additional floating-point control (FPC) register to support IEEE 754 modes and errors; • the floating-point support (FPS) extensions facility, which adds instructions to load and store floating-point numbers regardless of whether they're in hexadecimal or IEEE 754 format and to convert between those formats; • the hexadecimal floating-point (HFP) extensions facility, which adds new hexadecimal floating-point instructions corresponding to some binary floating-point instructions. Some PC-based IBM-compatible mainframes which provide ESA/390 processors in smaller machines have been released over time, but are only intended for software development. New facilities ESA/390 adds the following facilities ;All models :*Access-list-controlled protection ;Some models :*Concurrent sense :*PER 2 :*Storage-protection override :*Move-page facility 2 :*Square root :*String instruction :*Suppression on protection with virtual-address enhancement :*Set address space control fast :*Subspace group :*Called-space identification :*Checksum :*Compare and move extended :*Immediate and relative instructions :*Branch and set authority :*Perform locked operation :*Additional floating-point :*Program call fast :*Resume program :*Trap :*Extended TOD clock :*TOD-clock-control override :*Store system information :*Extended translation 1 :*Extended translation 2 :*z/Architecture (certain instructions) :*Enhanced input/output New instruction formats Some of the ESA/390 facilities introduce new instruction formats. This includes the RI, RIL and RSI formats used for relative branches. The immediate field for relative branches is always signed and in units of a halfword. New channel commands The following channel commands are new, or have their functionality changed, in ESA/390: ==Notes==