Computer Systems . CS208. Major Components of a Computer System. Processor (CPU) Runs program instructions Main Memory Storage for running programs and current data Secondary Storage Long-term program & data storage (hard disk, CD, etc) Input Devices
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The CPU controls all of the other resources within the system,
in order to accomplish a task.
Performs calculations and decisions
Arithmetic / Logic Unit
Coordinates processing steps
Small, fast storage areas for instructions and data
Special Purpose Registers contain specific information the CPU needs.
Not All Processors Are Created Equal
Newer machines use specialized processor chips that have been developed to speed up the processing of data.
Computer Memory - millions/billions of on/off charges
Storage is usually too large to be expressed in bytes or words. Instead we use:
Each memory cell has a numeric address, which uniquely identifies its location
Each memory cell stores a set number of bits (some computers use 8 bits/one byte, others use words)
A word is stored in
memory bytes.Main Memory
add r3, r1, r2Fetch-Decode-Execute Diagram
Get instruction and increment PC
Program Counter (PC)
add r3, r1, r2
Determine what the instruction is (add)
General Purpose Registers
In this case add r1 and r2 and put result in r3.
Then begin again by Fetching the instruction in 3024….
The hard disk is too slow to provide instructions to the CPU.
So programs are first loaded into main memory, which is much faster.
The CPU can then access the instructions more quickly.
When an instruction or data is accessed from main memory, it is placed in the cache. Second and subsequent use of the same instruction/data will then be faster, since it is accessed directly from the cache.