1. 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

2. 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

3. 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

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

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

6. Scheduling - JES

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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

15. 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

16. 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

17. 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

18. 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.

19. 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