carter tomlenovich

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Module One: CPU and Memory

Bus Width, Bus Speed, and Bandwidth

A bus is an electronic path over which data can travel.

Bus width and speed together determine the bandwidth. The amount of data actually transfered under real life conditions is called throughput


Word Size: The amount of data that a CPU can manipulate at one time - Typically 32 or 64 bits

Cache memory: Special group of extremely fast memory chips localed on the CPU. Sometimes can be off CPU but is usually close for easy accessibility.

  • Cache is split into 3 level
    • L1 being the fastest and L3 being the slowest.
    • More cache usually means more information for the CPU to process faster. -Cache can be dedicated to each core; may also have shared cache accessible by any core.
  • RAM (Random Access Memory): is the computers main memory
    • Consists of chips arranged on a circut board called a memory module (DIMM –> Dual Inline Memory Module)
    • VOLATILE: All contents of RAM are lost once the computer looses power.
  • Registers are high speed memory localtions build into the CPU

  • ROM (Read-only memory): Non-volatile memory that does not loose its contents when there is no power to the device. Hard drives with ferromagnetic material are being replaced with flash chips.


Transistors are the key element of any microprocessor, they are made of semi-conductor material that acts like a switch controlling the flow of electrons inside a chip.

  • CPU Core Components
    • The ALU (Arithmetic/Logic Unit) performs arithmetic involving integers and logical operations.
    • FPU (Floating Point Unit) perfoms decimal/floating point calculations.
    • The Control Unit coordinates and controls activitys within a CPU core.
    • The Prefetch Unit attempts to retieve data and instructions before they are neede for processing to avoid delays.
    • The Decode Unit translates insctructions from the Prefetch Unit to that they are understood by the Control Unit, ALU or FPU.
    • Cache and Registers store data and instructions for the CPU.
    • The Bus Interface Unit allows the core to communicate with other CPU components.

The Machine Cycle

  • Machine Cycle: The series of operations involved in the execution of a cingle machine level instruction. Can be memorized as FDES.
    • F: Fetch –> Instruction is fetched.
    • D: Decode –> The instruction is decoded.
    • E: Execute –> The instruction is executed.
    • S: The original data or the result is stored in the register.