CPU and Memory

CPU and Memory

1. Processing

   • Computers require an input hardware, processing hardware and output hardware.
   • CPU
     • executes programs using the fetch-decode-execute cycle
     • Memory
       • Stores program operations and data while the program is being executed. Types: Registers, cache, RAM, ROM and Virtual Memory
     • Storage
       • Stores programs and files long term, even when not in use. Types include: USB, SD Cards, Hard-Drives and SSDs
   • Graphics
     • Most computers have a separate GPU and CPU
     • Using the GPU to render images, frees up the CPU for other tasks
   • Performance
     • Benchmarking
       • A test used to access the performance of a computer. Different types of software are used depending on the computers purpose.
     • CPU speed (cycles per second) measured in Hertz
       • GHz
       • MHz
       • KHz
       • Hz
         • 1000 hertz is a kilo hertz

2. CPU and Memory

   • Factors that affect performance
     • Cores
       • CPU can contain one or more processing units (cores). A core contains a ALU, Control Unit and Registers.
       • Cores communicate through channels therefore doubling cores does not double speed
     • Clock Speed
       • The clock speed - also known as clock rate - indicates how fast the CPU can run. This is measured in megahertz (mHz) or gigahertz (gHz) and corresponds with how many instruction cycles the CPU can deal with in a second.
     • Cache Size
       • Cache is a small amount of memory which is a part of the CPU - closer to the CPU than RAM. It is used to temporarily hold instructions and data that the CPU is likely to reuse.
       • The CPU control unit checks the cache for instructions before the RAM.
       • Larger the Cache = the more data can be stored closer to the CPU
         • L! - part of the CPU chip, smallest and fastest to access (between 8KB and 64KB
         • L2/3 - larger, extra cache built between the CPU and RAM. More L2/3 = faster a computer can run
     • Processor Type
       • CISC
         • Complex Instruction Set Computing
         • Used by most laptops/desktops - made by Intel/AMD
       • RISC
         • Reduced Instruction Set Computing
         • Used in tablets/smartphones
       • Differences
         • RISC have less instructions. RISC more efficient at simpler tasks
         • Physical Size - CISC are larger and require more silicon
         • Speed - RISC run at a lower clock speed
         • Energy Consumption - CISC are larger and therefore use more energy
         • Design - RISC combines architecture onto one chip (SOC), whereas CISC are built seperatly a system with heat sinks and fans - RISC do not.
         • Cost - RISC use less power and are cheaper to make

3. Bridges

   • Bridges manage how data and instructions are transferred between devices

4. Memory

   • Memory is the area where the computer stores or remembers data. Memory provides the CPU with its instructions. AKA Primary Storage
     • Closer to CPU = quicker the CPU can access instructions
   • VOLATILE
     • Only stores information to run programs while the PC is on. Reset when the PC is turned off. Requires electricity to store data using transistors and capacitors
   • NON-VOLITILE
     • Retains data even when the computer is off. Examples in old computers: paper, punched tape and floppy disks
   • Latency is the time for components to respond to a request

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