lecture4 Intro .pdf
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FACULTY OF COMPUTERS AND INFORMATION
First Year (First Semester)
INTRODUCTION TO COMPUTERS
Dr. Hamdy M. Mousa
Introduction to Computers
How a Microprocessor Works
• Easiest way to visualize how computers work is to
think of them as enormous collections of switches.
• The microprocessor that makes up your personal
computer’s central processing unit, or CPU, is the
computer’s brains, messenger, ringmaster, and
• All the other components - RAM, disk drives, the
monitor - exist only to bridge the gap between you
and the processor.
• They take your data and turn it over to the processor
to manipulate; then they display the results.
How A Microprocessor Works
• The CPU isn’t the only microprocessor in PCs.
Coprocessors on graphics, 3-D accelerator, and
– The Pentium II holds 7.5 million transistors, or
tiny electronic switches.
• All the operations of the Pentium are
performed by signals turning on or off
different combinations of those switches.
Pentium Family of Processors
• The Pentium family of processors-including the
Pentium MMX, that help ensure data and code
move through the Pentium as fast as possible.
– The Pentium is the first Intel processor to have two
– The Pentium has a separate calculation unit that’s
optimized for handling floating-point numbers, or
numbers with decimal fractions, such as 1.2 or 35.8942.
• Pentium can take in data 64 bits at a time,
compared to the 32-bit data path of the 486
– the 486 has one storage area called a cache that holds
8 kilobytes at a time,
– the Pentium II has multiple caches totaling more than
1. A part of the Pentium microprocessor called the
bus interface unit (BIU) receives both data
and coded instructions from the computer’s
random access memory.
2. The bus interface unit sends data and code
along two separate paths that can each handle
64 bits at a time.
• One path leads to an 8K storage unit, or cache, used
• The other path leads to an identical cache used only for
the code that tells the processor what to do with that
• The data and code stay in the two caches until other
parts of the microprocessor need them.
3. While the code is waiting in its cache, the
branch predictor unit inspects the
instructions to determine which of the two
arithmetic logic units (ALUs) can handle
them more efficiently.
4. This inspection ensures that one of the
ALUs isn’t waiting while the other ALU
finishes executing another instruction.
5. If any floating point numbers need
processing, they are passed to a
specialized internal processor called the
floating point unit.
6. Within the execution unit, two
arithmetic logic units process all the
data consisting of only integers.
7. The two arithmetic logic units and
the floating point unit send the
results of their processing to the data
• The data cache sends the results to the
bus interface unit, which, in turn, sends
the results to RAM.