Introduction to Computer Systems - Fundamentals of Computer Organization and Architecture - page 5

complexity of computations within a single clock period. A number of studies from
the mid-1970s and early-1980s also identified that in typical programs more than
80% of the instructions executed are those using assignment statements, conditional
branching and procedure calls. It was also surprising to find out that simple assign-
ment statements constitute almost 50% of those operations. These findings caused a
different philosophy to emerge. This philosophy promotes the optimization of
architectures by speeding up those operations that are most frequently used while
reducing the instruction complexities and the number of addressing modes.
Machines following this philosophy have been referred to as reduced instructions
set computers (RISCs). Examples of RISCs include the Sun SPARC TM

and

MIPS TM machines.
The above two philosophies in architecture design have led to the unresolved
controversy as to which architecture style is “best.” It should, however, be men-
tioned that studies have indicated that RISC architectures would indeed lead to
faster execution of programs. The majority of contemporary microprocessor chips
seems to follow the RISC paradigm. In this topic we will present the salient features
and examples for both CISC and RISC machines.

1.3. TECHNOLOGICAL DEVELOPMENT

Computer technology has shown an unprecedented rate of improvement. This
includes the development of processors and memories. Indeed, it is the advances
in technology that have fueled the computer industry. The integration of numbers
of transistors (a transistor is a controlled on

off switch) into a single chip has
increased from a few hundred to millions. This impressive increase has been
made possible by the advances in the fabrication technology of transistors.
The scale of integration has grown from small-scale (SSI) to medium-scale (MSI)
to large-scale (LSI) to very large-scale integration (VLSI), and currently to wafer-
scale integration (WSI). Table 1.2 shows the typical numbers of devices per chip
in each of these technologies.
It should be mentioned that the continuous decrease in the minimum devices
feature size has led to a continuous increase in the number of devices per chip,

/

TABLE 1.2 Numbers of Devices per Chip

Integration Technology Typical number of devices Typical functions

SSI Bipolar 10-20 Gates and flip-flops

MSI Bipolar & MOS 50-100 Adders & counters

LSI Bipolar & MOS 100-10,000 ROM & RAM

VLSI CMOS (mostly) 10,000-5,000,000 Processors

WSI CMOS

. 5,000,000

DSP & special purposes

SSI, small-scale integration; MSI, medium-scale integration; LSI, large-scale integration; VLSI, very
large-scale integration; WSI, wafer-scale integration.