84 Implementing IBM Tape in i5/OS
3.1 System i architecture
This section describes the main characteristics of the System i architecture.
3.1.1 System i I/O architecture
IBM System i servers are entirely designed for I/O intensive business computing. The latest
POWER5+™ and POWER6™ microprocessor design and IBM System i unique processor
hierarchy lay the foundation for an outstanding performance and scalability. Workload is
offloaded from the CPU to dedicated input/output processors (IOPs) accommodated in I/O
cards that fit into Peripheral Component Interconnect (PCI) type slots on the system buses.
The IOPs transfer data to/from main storage and control the input/output adapters (IOAs)
which, for example, are the actual SCSI or Fiber Channel adapters for handling internal and
external storage device communications. More and more new System i I/O adapters are now
designed as IOP-less or smart IOAs which have the IOP functionality integrated into the IOA
and Licensed Internal Code to achieve a higher package density with no PCI slot required
anymore for an IOP.
The IBM System i
system busses are located in the Central Electronic Complex (CEC) and
in optional expansion units (also known as I/O towers) connected via High-Speed-Link (HSL)
copper or optical interfaces with which expansion units can be added concurrently to the
system. With the POWER6 models, a new 12X loop technology has been introduced based
on InfiniBand® technology offering up to 50% more bandwidth than previous HSL technology.
3.1.2 Technology Independent Machine Interface
A unique design going back to the early days of the System/38™ which sets the AS/400,
iSeries and System i apart for other computer systems is the strict separation of
Licensed Internal Code
(SLIC) and the operating system i5/OS by the Technology
Independent Machine Interface
(TIMI) shown in Figure 3-1.
Chapter 3. Overview of the IBM System i platform 85
Figure 3-1 System i Technology Independent Machine Interface (TIMI)
This architecture makes both the i5/OS operating system itself and any user applications
running above TIMI independent from any specific hardware implementation, which is
completely being dealt with by SLIC. A classic example of the hardware independence was
the transition from a 48 bit complex instruction set computing (CISC) to a 64 bit reduced
instruction set computing (RISC) of the AS/400 in 1995 without requiring any recompiling or
rewriting of user applications.
Clearly the benefits of the TIMI architecture are a very robust system design, because
applications cannot directly communicate and therewith manipulate the hardware, as well as
offering an excellent investment protection for any software applications being immune to
underlying hardware changes.
System i Hardware
File systems Java/JVM
Security Storage management
Encryption Graphical interface
DB2 UDB TCP/IP
Internet services Online help
Spooling Performance tuning
Systems mgmt Graphical interface
OLTP Job scheduling
Communications Programming interfaces
DB2 UDB Access Shell and utilities
Technology Independent Machine Interface