Overview Offspring of S/390 operating system Same reliability, performance, scalability, and cost efficiency OS/390 geared more towards e-business and client/server interaction Allows greater flexibility Allows companies to customize their system Various elements that can be added to base OS

Customizing the System BDT File –To-File- allows users from one OS/390 system to copy data from another OS/390 system C/C++ with or without Debug Tool IBM Communications Server Security Level 3- highest level of security for a TCP/IP network environment, supporting packet filtering, tunnels and NAT OCFS Security Level 3- working with Cryptographic services (base element), provides weak and strong software cryptographic services, along with various data libraries

Real World Use 90% of the world’s largest corporations run OS/390 as central OS Running on Hitachi, Fujitsu, IBM S/390 and Amdahl hardware Close to 1,400 Independent Software Vendors take advantage of OS/390 PeopleSoft, Lotus Domino, SAP R/3

Scheduling JES- Job Entry System BAP- Base Control Program Before and after running the program BAP- Base Control Program During processing

Scheduling - JES HASP- Houston Automatic Spooling Priority JES2 – Single processor JES3 – Multi processor JCL – Job Control Language

Scheduling - JES

Software and Hardware The OS/390 is intimately tied to its hardware The hardware and the software often evolved in tandem Any discussion of OS/390 processor modes inevitably becomes a discussion of S/390 processor configuration and availability

Processor Performance Despite its limited market the OS/390 is relatively unchallenged in the area of high-end mainframe number crunching Size, power and security make it useful for mission-critical systems like finance-oriented transaction systems Some supporters claim that up to 90% of all high-end business data is held on an S/390 system Such a claim is questionable; IBM has seen a decline in S/390 revenue in the past ten years with the increase of “simpler and smaller” UNIX and Windows NT solutions

A Well-Endowed Machine There is still no doubt that the S/390 systems offer serious high-end computing power. Two kinds of processor upgrades: vertical and horizontal Horizontal: replacing the current processor with a different one designed for that system Vertical: adding new processors to the system One measure of vertical growth efficiency is its “linear scalability.” S/390 systems have near-perfect linear scalability. Ideal for multiprocessing

A Short Processor History OS/390 evolved from first OS/360 system First developed in 1964 by Gene Amdahl, Gerry Blaauw and Fred Brooks at IBM Originally a uniprocessor, single-batch system Some highlights: 1968: first two-way SMP concurrent batch system ever 1983: the 3084 system featured the first four-way SMP architecture. 1999: the S/390 featured twelve-way SMP architecture with cryptographic coprocessor Up to 32 may be clustered into a Sysplex 2000: the vSeries 900 was released with 16-way SMP and 64-bit addressing

Interesting Processor Features System can be divided into logical partitions using Processor Resource / System Manager (PR/SM) Each partition can feature different installations and restrict user access Double Operation Execution Each operation is executed twice, in parallel The results are compared and upon mismatch the operation is performed again CPUs feature Cryptographic Facility Special instructions that support identification and key management Improves security by a factor of 19 when compared to software generation of 512 bit RSA keys

Memory Management In the OS/390 there are three levels of memory managed by the operating system: central storage expanded storage page data sets on disk

Memory Management Central storage manages itself based on the most recently used algorithm and workload priority The Real Storage Manager allocates storage on the basis of demand by assigning frames from an available frame queue, also known as AFQ

Memory Management OS/390 implemented the idea of expanded storage to accommodate inactive pages Expanded storage is addressable only as pages and is not accessible to the I/O subsystem or normal CPU instructions

Memory Management Pages with low priority or not recently used are paged out to expanded memory. Block Paging - Pages that need to be paged out are grouped together and written out as a block in one I/O. More efficient than normal paging in its use of I/O

File Management The OS/390 file management system uses a heirarchical approach Features included in the system: Directory support Current directory and home support Absolute and relative path names Hard links and symbolic links Extended attribute support Save and restore support

File Management The OS/390 heirarchical file system views the entire file heirarchy as a collection of heirarchical file system data sets The data set is the fundamental unit of data management in OS/390

Process Management The job as a whole is usually thought of a as a single transaction with a single purpose. There is a specific language for the definition of such jobs, namely Job Control Language.

Process Management For every job submitted OS/390 needs to know: Where to find the appropriate input How to process that input What to do with the resulting output