Advanced Personal Computer (PC) Concepts

After the initial years of the PC (let's say 1980-1986), the search for more efficient PCs, capable of greater processing power, speed, and felexibility went into high gear.

PIPELINING:

The term 'pipelining' was introduced in the early 1980's. It was based on the fact that a computer can do more than a single thing, or instruction, at a time! Older PCs had basically a 3 step process for executing an instruction.

  1. Fetch Cycle - gets the next instruction to be executed into a register.
  2. Decode Cycle - break down the instruction to see what to do.
  3. Execute Cycle - do the thing the instruction is supposed to do.

You see an instruction as "ADD A to B giving X". In computer instructions, this may take up to 20 simple instructions. Special computer programs called "compilers" take the "ADD A to B giving X", and translate them into "machine" language instructions which can be understood in your CPU!

So, all computer instructions are a set of binary 1's and 0's, arranged in a specific sequence to represent a machine or computer language instruction. A machine language instruction can be decoded and executed by the microprocessor (CPU).

Now, when a computer program is run on a computer, it is first loaded into a 640KB piece of memory. This 640 KB can be the conventional memory, or it can be a part of your extended memory (See Memory)

  1. Each instruction is moved from memory to a register in the CPU by the fetch cycle.
  2. The instruction is then decoded, it determines that it is an add instruction, then the data such as A and B in the example above are retrieved and put in registers.
  3. The data in A and in B are added together and stored in a register.
  4. The register storing the sum of A and B is moved to a location specified as X. X takes on the value of the sum.
  5. The next instruction is 'fetched' from memory and the cycle goes on.
  6. Actually the steps above may be many small instructions. We will worry about details later.
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