RISC
The concept was developed by John Cocke of IBM Research during
1974. His argument was based upon the notion that a computer uses
only 20% of the instructions, making the other 80% superfluous to
requirement. A processor based upon this concept would use few
instructions, which would require fewer transistors, and make them
cheaper to manufacture. By reducing the number of transistors and
instructions to only those most frequently used, the computer would
get more done in a shorter amount of time. The term 'RISC' (short
for Reduced Instruction Set Computer) was later coined by David
Patterson, a teacher at the University of California in Berkeley.
The RISC concept was used to simplify the design of the IBM
PC/XT, and was later used in the IBM RISC System/6000 and Sun
Microsystems' SPARC microprocessors. The latter CPU led to
the founding of MIPS Technologies, who developed the M.I.P.S. RISC
microprocessor (Microprocessor without Interlocked Pipe Stages).
Many of the MIPS architects also played an instrumental role in the
creation of the Motorola 68000, as used in the first Amigas (MIPS
Technologies were later bought by Silicon Graphics).. The MIPS
processor has continued development, remaining a popular choice in
embedded and low-end market. At one time, it was suspected the
Amiga MCC would use this CPU to reduce the cost of manufacture.
However, the consumer desktop market is limited, only the PowerPC
processor remains popular in the choice of RISC alternatives. This
is mainly due to Apple's continuous use of the series for its
PowerMac range.
CISC
CISC (Complex Instruction Set Computer) is a retroactive definition
that was introduced to distinguish the design from RISC
microprocessors. In contrast to RISC, CISC chips have a large
amount of different and complex instruction. The argument for its
continued use indicates that the chip designers should make life
easier for the programmer by reducing the amount of instructions
required to program the CPU. Due to the high cost of memory and
storage CISC microprocessors were considered superior due to the
requirements for small, fast code. In an age of dwindling memory
hard disk prices, code size has become a non-issue (MS Windows,
hello?). However, CISC-based systems still cover the vast majority
of the consumer desktop market. The majority of these systems are
based upon the x86 architecture or a variant. The Amiga, Atari, and
pre-1994 Macintosh systems also use a CISC microprocessor.
RISC Vs. CISC
The argument over which concept is better has been repeated over
the past few years. Macintosh owners have elevated the argument to
a pseudo religious level in support of their RISC-based God (the
PowerPC sits next to the Steve Jobs statue on every Mac altar).
Both positions have been blurred by the argument that we have
entered a Post-RISC stage.
RISC: For and Against
RISC supporters argue that it the way of the future, producing
faster and cheaper processors - an Apple Mac G3 offers a
significant performance advantage over its Intel equivalent.
Instructions are executed over 4x faster providing a significant
performance boost! However, RISC chips require more lines of code
to produce the same results and are increasingly complex. This will
increase the size of the application and the amount of overhead
required. RISC developers have also failed to remain in competition
with CISC alternatives. The Macintosh market has been damaged by
several problems that have affected the availability of 500MHz+
PowerPC chips. In contrast, the PC compatible market has stormed
ahead and has broken the 1GHz barrier. Despite the speed advantages
of the RISC processor, it cannot compete with a CISC CPU that
boasts twice the number of clock cycles.
CISC: For and Against
As discussed above, CISC microprocessors are more expensive to make
than their RISC cousins. However, the average Macintosh is more
expensive than the WIntel PC. This is caused by one factor that the
RISC manufacturers have no influence over - market factors. In
particular, the WIntel market has become the definition of personal
computing, creating a demand from people who have not used a
computer previous. The x86 market has been opened by the
development of several competing processors, from the likes of AMD,
Cyrix, and Intel. This has continually reduced the price of a CPU
of many months. In contrast, the PowerPC Macintosh market is
dictated by Apple. This reduces the cost of x86 - based
microprocessors, while the PowerPC market remains stagnant.
Post-RISC
As the world enters the 21st century the CISC Vs. RISC arguments
have been swept aside by the recognition that neither terms are
accurate in their description. The definition of 'Reduced' and
'Complex' instructions has begun to blur, RISC chips have increased
in their complexity (compare the PPC 601 to the G4 as an example)
and CISC chips have become more efficient. The result are
processors that are defined as RISC or CISC only by their
ancestry. The PowerPC 601, for example, supports more
instructions than the Pentium. Yet the Pentium is a CISC chip,
while the 601 is considered to be RISC. CISC chips have also gained
techniques associated with RISC processors. Intel describe the
Pentium II as a CRISC processor, while AMD use a RISC architecture
but remain compatible with the dominant x86 CISC processors. Thus
it is no longer important which camp the processor comes from, the
emphasis has once-again been placed upon the operating system and
the speed that it can execute instructions.
EPIC
In the aftermath of the CISC-RISC conflict, a new enemy has
appeared to threaten the peace. EPIC (Explicitly Parallel
Instruction Computing) was developed by Intel for the server
market, thought it will undoubtedly appear in desktops over the
next few years. The first EPIC processor will be the 64-bit Merced,
due for release sometime during 2001 (or 2002, 2003, etc.). The
market may be divided between combined CISC-RISC systems in the
low-end and EPIC in the high-end.
Famous RISC microprocessors
801
To prove that his RISC concept was sound, John
Cocke created the 801 prototype microprocessor (1975). It was never
marketed but plays a pivotal role in computer history, becoming the
first RISC microprocessor.
RISC 1 and 2
The first "proper" RISC chips were created at Berkeley
University in 1985.
ARM
One of the most well known RISC developers is Cambridge based
Advanced Research Machines (originally Acorn Research Machines).
Their ARM and StrongARM chips power the old Acorn Archimedes and
the Apple Newton handwriting recognition systems. Since the
unbundling of ARM from Acorn, Intel have invested a considerable
amount of money in the company and have utilized the technology in
their processor design. One of the main advantages for the ARM is
the price- it costs less than £10.
If Samsung had bought the Amiga in 1994, they would possibly have
used the chip to power the low-end Amigas.
External Links
RISC Vs.
CISC: The Post-RISC Era
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