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Mainframe and Open Systems
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Definitions
Mainframe any of the large, mature, proprietary computingsystems
built primarily by IBM IBM Operating Systems: MVS, OS/390, TPF, VM,
z/OS
Separate, dedicated I/O processing hardware in addition to the
CPUs
Methods used for I/O are unique to this environment and
generally producedby IBM exclusively
These have a mature storage management environment
Open Systems any of the computing platforms built by avariety of
vendors using open hardware and softwarestandards Operating
Systems: UNIX/Linux, Microsoft Windows, Novell NetWare
Similar methods to perform I/O, but entirely different than
mainframes
I/O device drivers are constructed in layers, and can be
produced byvendors other than the vendor of the operating
system
Storage management environment is less mature than
mainframes
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Comparisons
Mainframe I/O is done to records
Physically written as CKD
Standard hardware (channel
subsystem) and operatingsystem
Protected environment no thirdparty software or hardware
hasaccess to system resources
Difficult to change operational
environment Caching done in storage systemwith special
commands
Device sharing is basic to OS
Open Systems I/O is done to files blocks
Physically written as FBA
Various versions of operatingsystems and many flavors of
device drivers and adapters Third party software (device
drivers) have access to systemresources
Flexible environment to allownew capabilities
IFS, filter drivers, redirectors
Caching typically done in systemmemory
Device sharing not a basicfunction
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App licat ion /
Database
Operating System
File System
Device Driver
Interface Hardware
Device
Open Systems I/O
Appl ication
Access
Method
IOS
Channel
Subsystem
Storage
System
Interface such as ESCON
VSAM, QSAM, etc.
Get, Put
I/O Supervisor
OS/390 I/OComparisons
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Files and Data Sets
Mainframe (Data Sets)
Defined types: Physical Sequential, Partitioned, VSAM, etc.
UNIX and Windows have only one basic data file type
Elements within Partitioned Data Sets are called members UNIX
and Windows have no direct equivalent to PDS members
UNIX and Windows (Files)
File types: files and directories Directories can have
sub-directories, many levels deep
No directory hierarchy structure on mainframe
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REFERENCETranslation Table
OS/390 Open SystemVTOC Superblock
DSCB inode
record file handle: offset
I/O Task NT: IRP
IOS NT: I/O Manager, Unix: I/O Subsystem
Task Thread
TSO, ISPF Shell (C Shell, Bourne Shell)Nucleus Kernel
Access Method - none -
Master catalog file system
IOS Device drivers (roughly)
RACF Kerberos
Address Space ID Process ID
Common Storage (CSA) shared memory segment
IPL boot
Job batch processprivileged mode superuser mode
SVC (supervisor call) system call
crash panic, BSOD
custom access method Raw I/O
- none - Memory mapped I/O
DASD disk
dataset file
