PowerPC
PPC
(PPC) A RISC microprocessor designed
to meet a standard which was jointly designed by Motorola,
IBM, and Apple Computer (the PowerPC Alliance). The
PowerPC standard specifies a common instruction set
architecture (ISA), allowing anyone to design and fabricate
PowerPC processors, which will run the same code. The PowerPC
architecture is based on the IBM POWER architecture, used in
IBM's RS/6000 workstations. Currently IBM and
Motorola are working on PowerPC chips.
The PowerPC standard specifies both 32-bit and 64-bit data
paths. Early implementations were 32-bit (e.g. PowerPC
601); later higher-performance implementations were 64-bit
(e.g. PowerPC 620). A PowerPC has 32 integer registers (32-
or 64 bit) and 32 floating-point (IEEE standard 64 bit)
floating-point registers.
The POWER CPU chip and PowerPC have a (large) common core, but
both have instructions that the other doesn't. The PowerPC
offers the following features that POWER does not:
Support for running in little-endian mode.
Addition of single precision floating-point operations.
Control of branch prediction direction.
A hardware coherency model (not in Book I).
Some other floating-point instructions (some optional).
The real time clock (upper and lower) was replaced with the
time base registers (upper and lower), which don't count in
sec/ns (the decrementer also changed).
64-bit instruction operands, registers, etc. (in 64 bit
processors).
See also PowerOpen, PowerPC Platform (PReP).
<IBM PPC info>.
<gopher://info.hed.apple.com/>, "Apple Corporate News/"
(press releases), "Apple Technologies/" and "Product
Information/". <gopher://ike.engr.washington.edu/>, "IBM
General News/", "IBM Product Announcements/", "IBM Detailed
Product Announcements/", "IBM Hardware Catalog/".
Usenet newsgroups: <news:comp.sys.powerpc>,
<news:comp.sys.mac.hardware>.
["Microprocessor Report", 16 October 1991].
(1994-09-30)
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