Since December, 2001, IBM designates all its mainframes with the name eserver zSeries, with the e depicted in IBM's well-known red trademarked symbol. Nonetheless, the term zSeries now popularly refers only to IBM's newest line of 64-bit mainframes, starting with the zSeries 900.

zSeries servers succeeded the IBM System/390 (S/390 for short). zSeries servers are the direct, lineal descendents of the IBM System/360, announced in 1964, and the 1970s System/370. Applications written for the 24-bit System/360 can still run, unmodified, on the newest zSeries 990 four decades later, with few exceptions.

Major features of the eserver zSeries family:

• Based on z/Architecture (64-bit real and virtual addresses)
• Offers up to 32 central processors (CPs) per frame (rack) coupled in up to a 32-frame Sysplex  — with each frame physically separated up to 100 kilometers
• Supports the Linux, z/OS, z/VM, VSE, TPF, and MUSIC/SP operating systems
• S/390 ESA applications are fully compatible with z/Architecture

In May 2003, IBM announced the zSeries 990 family, which began shipping at the end of that October. These models deliver nearly three times the total system capacity, four times the memory, and over four times the I/O and networking bandwidth of the z900 family.

The zSeries 990 Model D32 is currently the most powerful IBM mainframe computer available, reportedly capable of performing more than 9,000,000,000 core instructions per second.

A direct comparison of zSeries servers with other computing platforms is difficult. zSeries servers are unique in providing processing power for business-critical, high volume transaction processing and databases. For example, zSeries servers offload such functions as I/O processing, cryptography, memory control, and various service functions to dedicated processors. These "extra" processors are in addition to the 32 main CPs per frame. The zSeries servers also execute every instruction twice in order to assure processing integrity. If the instruction results differ, the zSeries server retries the instruction. If the instruction still fails, the zSeries server will shut down the failing processor and shift workload, "in flight," to any surviving processors, including one or more spares. This shift occurs transparently to software applications. The same concept extends to coupled frames separated by up to 100 kilometers in a Geographically Dispersed Parallel Sysplex .

zSeries servers are well regarded for their reliability, availability, integrity, and mixed workload performance. They tend to have higher costs of acquisition and lower costs of ownership than other platforms, especially when running a variety of business-critical applications concurrently (so-called mixed workload ).

See also

• List of IBM products
• Linux on zSeries
• zAAP

External links

• http://www.ibm.com/servers/eserver/zseries/
• http://www.ibm.com/servers/eserver/zseries/z990/
• http://www.ibm.com/servers/eserver/zseries/announce/z990/
• The Hercules System/370, ESA/390, and z/Architecture Emulator