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History of IBM mainframes, 1952–present
Market name
Architecture

IBM Enterprise Systems Architecture is an instruction set architecture introduced by IBM as ESA/370 in 1988. It is based on the IBM System/370-XA architecture.

It extended the dual-address-space mechanism introduced in later IBM System/370 models by adding a new mode in which general-purpose registers 1-15 are each associated with an access register referring to an address space, with instruction operands whose address is computed with a given general-purpose register as a base register will be in the address space referred to by the corresponding address register.

The later ESA/390, introduced in 1990, added a facility to allow device descriptions to be read using channel commands and, in later models, added instructions to perform IEEE 754 floating-point operations and increased the number of floating-point registers from 4 to 16.

Enterprise Systems Architecture is essentially a 32-bit architecture; as with System/360, System/370, and 370-XA, the general-purpose registers are 32 bits long, and the arithmetic instructions support 32-bit arithmetic. Only byte-addressable real memory (Central Storage) and Virtual Storage addressing is limited to 31 bits, as is the case with 370-XA. (IBM reserved the most significant bit to easily support applications expecting 24-bit addressing, as well as to sidestep a problem with extending two instructions to handle 32-bit unsigned addresses.) It maintains problem state backward compatibility dating back to 1964 with the 24-bit-address/32-bit-data (System/360 and System/370) and subsequent 24/31-bit-address/32-bit-data architecture (System/370-XA). However, the I/O subsystem is based on System/370 Extended Architecture (S/370-XA), not on the original S/370 I/O instructions.

ESA/370 architecture

On February 15, 1988, IBM announced[6][7] 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.[8] 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.[11][12]

Starting with the System/390 G5,[9][10] IBM introduced:[13]

  • 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[14] 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 instruction
  • 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 channel commands

The following channel commands[f] are new, or have their functionality changed, in ESA/390:[12]

ESA/390 I/O-Device Commands
Command Bit Position
0 1 2 3 4 5 6 7
Read configuration data D D D D D D D 0
Read node identifier D D D D D D D 0
Sense ID 1 1 1 0 0 1 0 0
Set interface identifier D D D D D D D 1
Note:
D Device dependent. The command code, if any, recognized by an I/O device may be obtained by using a sense-ID command.

Notes

  1. ^ The number and format of floating-point registers depends on the installed features:
    ESA/370
    ESA/390 without the new floating-point facilities
    Only the hexadecimal floating point (HFP) registers FP0, FP2, FP4 and FP6 exist
    ESA/390 with the new floating-point facilities
    FP0_FP15 may be HFP or IEEE floating point
  2. ^ ESA/390 with the new floating-point facilities
  3. ^ ESA/390 with the new floating-point facilities
  4. ^ Bit 22 is renamed as HFP exponent underflow in ESA/390
  5. ^ Bit 23 is renamed as HFP significance in ESA/390
  6. ^ The data returned by Sense ID include the command codes for Read configuration data, Read node identifier and Set interface identifier.

References

S370-ESA
IBM Enterprise Systems Architecture/370 Principles of Operation (PDF) (First ed.). IBM. August 1988. SA22-7200-0.
S/390-ESA
IBM Enterprise Systems Architecture/390 Principles of Operation (PDF) (Ninth ed.). IBM. June 2003. SA22-7201-08.
  1. ^ S370-ESA, p. 5-30, Access-list-Entry Token.
  2. ^ S370-ESA, pp. 4-7–4-9, Figure 4-3 Assignment of Control-Register Fields.
  3. ^ S390-ESA, pp. 4-8–4-10, Figure 4-3 Assignment of Control-Register Fields.
  4. ^ S370-ESA, p. 4-5, Program-Status-Word Format.
  5. ^ S390-ESA, p. 4-5, Program-Status-Word Format.
  6. ^ "IBM 3090 PROCESSOR UNIT MODELS 280E AND 500E AND IBM 3090 PROCESSOR UNIT MODEL 300E TO 400E UPGRADE". Announcement Letters. IBM. February 15, 1988. 188-038.
  7. ^ "ENTERPRISE SYSTEMS ARCHITECTURE/370 (TM) AND MVS/SYSTEM PRODUCT VERSION 3". Announcement Letters. IBM. February 15, 1988. 288-059.
  8. ^ S370-ESA.
  9. ^ a b Slegel, Timothy J. (August 17, 1998). "IBM S/390 G5 Microprocessor" (PDF). Hot Chips.
  10. ^ a b Schwarz, E. M.; Krygowski, C. A. (September 1, 1999). "The S/390 G5 floating-point unit". IBM Journal of Research and Development. 43 (5): 707–721. doi:10.1147/rd.435.0707.
  11. ^ S390-ESA, pp. 1–8.
  12. ^ a b Enterprise Systems Architecture/390 Common I/O-Device Commands, Second Edition, IBM, April 1992, SA22-7204-01
  13. ^ S390-ESA, pp. 1-3–1-4, Highlights of ESA/390.
  14. ^ S390-ESA, pp. D-1–D-7, Appendix D. Comparison between ESA/370 and ESA/390.
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