WHAT ARE THE DIFF B/W 32 BIT OS AND 64 BIT OS

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WHAT ARE THE DIFF B/W 32 BIT OS AND 64 BIT OS..

A change from a 32-bit to a 64-bit architecture is a
fundamental alteration, as most operating systems must be
extensively modified to take advantage of the new
architecture. Other software must also be ported to use the
new capabilities; older software is usually supported
through either a hardware compatibility mode (in which the
new processors support the older 32-bit version of the
instruction set as well as the 64-bit version), through
software emulation, or by the actual implementation of a 32-
bit processor core within the 64-bit processor (as with the
Itanium processors from Intel, which include an x86
processor core to run 32-bit x86 applications). The
operating systems for those 64-bit architectures generally
support both 32-bit and 64-bit applications[11].
One significant exception to this is the AS/400, whose
software runs on a virtual ISA, called TIMI (Technology
Independent Machine Interface) which is translated to native
machine code by low-level software before being executed.
The low-level software is all that has to be rewritten to
move the entire OS and all software to a new platform, such
as when IBM transitioned their line from the older 32/48-bit
"IMPI" instruction set to 64-bit PowerPC (IMPI wasn't
anything like 32-bit PowerPC, so this was an even bigger
transition than from a 32-bit version of an instruction set
to a 64-bit version of the same instruction set).
While 64-bit architectures indisputably make working with
large data sets in applications such as digital video,
scientific computing, and large databases easier, there has
been considerable debate as to whether they or their 32-bit
compatibility modes will be faster than comparably-priced
32-bit systems for other tasks. In x86-64 architecture
(AMD64), the majority of the 32-bit operating systems and
applications are able to run smoothly on the 64-bit
hardware.
Sun's 64-bit Java virtual machines are slower to start up
than their 32-bit virtual machines because Sun has only
implemented the "server" JIT compiler (C2) for 64-bit
platforms.[12] The "client" JIT compiler (C1), which
produces less efficient code but compiles much faster, is
unavailable on 64-bit platforms.
Speed is not the only factor to consider in a comparison of
32-bit and 64-bit processors. Applications such as multi-
tasking, stress testing, and clustering—for HPC (high-
performance computing)—may be more suited to a 64-bit
architecture when deployed appropriately. 64-bit clusters
have been widely deployed in large organizations such as
IBM, HP and Microsoft, for this reason.