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Architecture
This diagram describes how PASE for iSeries fits with the traditional iSeries architecture.
The underlying technology that makes OS/400 PASE possible is the common Power PC processor that has been shared by pSeries and iSeries. It is a high-speed chip that provides multiple addressing modes. By using the PowerPC AS and PowerPC chip modes in a controlled, secure way, OS/400 PASE helps the iSeries harness this strength. OS/400 PowerPC AS supports both 32-bit and 64-bit modes.
The System Licensed Internal Code (SLIC) kernel controls the use of the hardware and the type of address space that can be used. SLIC is a common kernel under the OS/400 PASE shared libraries and OS/400. The services that SLIC provides are common to both the Integrated Language Environment (ILE) and OS/400 PASE environments, creating a well-integrated system, regardless of which environment the application is using.
The environments share the same file systems, security mechanisms, threading mechanisms, and can even share memory and connect to the same sockets (with a little care to note pointer format expectations and character set being shared).
SLIC and OS/400 work together to provide an object-based operating system on iSeries. OS/400 PASE has not caused creation of new system objects -- it uses the ones that were already built to support standard APIs for ILE. This facilitates sharing of files and other system information between application code and also gives OS/400 PASE an operational view that is just what iSeries customers expect. OS/400 PASE for iSeries applications look like ILE Java or other applications to iSeries operators.
Programs and files for OS/400 PASE applications are saved and restored in familiar ways, without the operator having to know that they are using any new system facilities.
As much of OS/400 sits architecturally on top of the Technology Independent Machine Interface (TIMI) OS/400 PASE sits architecturally on top of the syscall interface. It looks like AIX in this respect. There is a protection layer between the kernel services for OS/400 PASE and non-privileged system or user code as there is for OS/400, but the syscall is not designed to provide the same virtual machine as the TIMI. OS/400 has the capability to move applications, which maintain their intermediate form, to new hardware architectures (i.e., CISC to RISC) without recompiling. This level of compatibility is not provided by OS/400 PASE or expected by Unix solution providers.
OS/400 PASE applications will be recompiled when the customer moves to new hardware architecture, as one would expect with an AIX application making the same transition, since they directly access the hardware processor. However, within an architecture family, upgrades are often transparent to the application
OS/400 PASE is called from ILE applications. This is how it is started, running in an OS/400 job. Applications that use OS/400 PASE are fully integrated in the customer's iSeries workload and look no different operationally. OS/400 PASE for iSeries can also call ILE functions including both application code and OS/400 system services. To an iSeries programmer, OS/400 PASE looks like just another program model. To a UNIX programmer, OS/400 PASE provides the familiar AIX application binary interface (ABI) for their porting process.
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