The Central Processing Unit

The Central Processing Unit

Measuring the performance of a CPU: (pg 85)
Speed, measured in Mhz
Efficiency of program code
Amount of memory that can be addressed
Amount of cache memory
Word size
Data path size

Mhz (Clock beats per second)
1 Mhz = 1 million clock beats per second
1 clock beat is the smallest unit of time in which processing happens
More clock beats per second = faster processor = more powerful computer

Efficiency of program code
Each CPU has a set of internal instructions
Efficiency refers to how many clock beats an instruction needs
Fewer number of clock beats per instruction = more efficient program code

Amount of memory that can be addressed
Each item placed into memory by the CPU must have a memory address
The CPU cannot use memory that it cannot address

Amount of cache memory
Cache memory is temporary storage for the CPU
The CPU stores frequently used data in cache, rather than RAM
Retrieving data from cache memory takes the CPU only 4% of the time it takes to retrieve data from RAM

Word size / Data path size
The CPU recognizes all communication in electrical signals
High voltage (3.3V or 5V) = 1
Low voltage or no voltage = 0
Individual bits (either 1 or 0) have little meaning to a CPU
A group of bits make a word
Most instructions are constructed of words

Word size refers to the size of the word the CPU can process internally
Data path size refers to the size of the word that the system bus can transport into the CPU

RISC – Reduced Instruction Set Computer
Fewer internal instructions
All instructions are the same size, so processing is more efficient
RISC processors demand more from the software they run, because they have fewer internal instructions
AMD is one example of a RISC processor

CISC – Complex Instruction Set Computer
Contains many more internal instructions than RISC
Instructions vary in size and require more complex circuitry to decode
CISC processors demand more from the hardware that runs them, but can support more software than RISC
Pentium is a CISC processor

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Note: These are notes from my lectures as an IT instructor. Notes are from 1999-2001, so there may be little relevance to contemporary technologies. Still, it seemed like a shame to delete all of this work, so here they are. I hope someone finds them helpful.