ZSeries

From Exampleproblems

The correct title of this article is zSeries. The initial letter is capitalized due to technical restrictions.

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. In mid-2005, IBM began using a new brand name (System z9), coinciding with the announcement of the company's Model 109 server. However, "zSeries" is still the most popular way to refer to all IBM mainframe servers.

zSeries/z9 servers succeeded the IBM System/390 (S/390 for short). zSeries/z9 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 System z9 over four decades later, with few exceptions.

Major features of the eServer zSeries/z9 family:

Based on z/Architecture (64-bit real and virtual addresses)
Offers up to 54 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, z/VSE, z/TPF, and MUSIC/SP operating systems
S/390 ESA (31-bit) applications are fully compatible with z/Architecture

The System z9-109 (S54), with up to 54 "characterizable" PUs (processors), is currently the most powerful IBM mainframe available, reportedly capable of performing approximately 18,660,000,000 core instructions per second. A single S54 can typically process one billion or more business transactions per day. The 54 PUs can be characterized (configured) for a variety of purposes including general purpose processing (CPs), zAAPs, IFLs, and ICFs (coupling facilities).

A direct comparison of zSeries/z9 servers with other computing platforms is difficult. zSeries/z9 servers are unique in providing processing power for business-critical, high volume transaction processing and databases. For example, zSeries/z9 servers offload such functions as I/O processing, cryptography, memory control, and various service functions (such as accounting and logging) to dedicated processors. These "extra" processors are in addition to the (up to) 54 main CPs per frame. The zSeries/z9 servers also effectively execute every instruction twice in order to assure processing integrity. If the instruction results differ, the zSeries/z9 server retries the instruction. If the instruction still fails, the zSeries/z9 server will shut down the failing processor and shift workload, "in flight," to any surviving processors, including one or more spares. (The System z9, for example, always has at least two spares available.) The zSeries/z9 then "calls home" (automatically places a service call to IBM), and an IBM service technician soon arrives with a replacement part (called a "book," consisting of a group of processors). The technician installs the new book and removes the old one without interruption to running applications (z9) or with minimal disruption (zSeries). (Note that zSeries/z9 processors have a reported 40 year MTBF.) Similar design redundancies exist in memory, I/O, power, cooling, and other zSeries/z9 subsystems. All these features exist at the hardware and microcode level, without special application programming. The same concepts extend to coupled frames separated by up to 100 kilometers in a Geographically Dispersed Parallel Sysplex.

zSeries/z9 servers are well regarded for their reliability, availability, integrity, and mixed workload performance -- characteristics not typically measured in computing benchmarks. They tend to have higher costs of acquisition ("price") and lower costs of ownership ("TCO") than other platforms, especially when running a variety of business-critical applications concurrently (so-called mixed workload). They are the enterprise workhorses in numerous industries including government, financial services, retail, and manufacturing.