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.
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).
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] 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.