1.2 Memory And 1.3 Storage

1.2 Memory And 1.3 Storage

1. Why do we need it?

   • Secondary Storage
     • Characteristics
       • Capacity
       • Reliability
       • Cost
       • speed
       • Durability
       • Portability
     • Magnetic
       • Magnetic storage or magnetic recording is the storage of data on a magnetised medium. Magnetic storage uses different patterns of magnetisation in a magnetisable material to store data and is a form of non-volatile memory. The information is accessed using one or more read/write heads.
     • Optical
       • Optical storage is the storage of data on an optically readable medium. Data is recorded by making marks in a pattern that can be read back with the aid of light, usually a beam of laser light precisely focused on a spinning optical disc.
     • Solid states
       • Solid-state storage (SSS) is a type of computer storage media made from silicon microchips. SSS stores data electronically instead of magnetically, as spinning hard disk drives (HDDs) or magnetic oxide tape do.

2. Hardware :The physical (you can touch them) components that make up a computer system.

   • Mouse
   • keyboard
   • Monitor
   • Fan

3. Architecture

   • Von Neumann Architecture: Traditional computer architecture that forms the basis of most digital computer systems. Programs and data can be stored in the same memory unit.
   • Harvard Architecture: Stores programs and data in separate memory units. Entering or altering programs is harder with this method

4. FDE cylce

   • 1. The processor checks the program counter to see which instruction to run next.
   • 2. The program counter gives an address value in the memory of where the next instruction is.
   • 3. The processor fetches the instruction value from this memory location.
   • 4. Once the instruction has been fetched, it needs to be decoded and executed. For example, this could involve taking one value, putting it into the ALU, then taking a different value from a register and adding the two together.
   • 5. Once this is complete, the processor goes back to the program counter to find the next instruction.
   • 6. This cycle is repeated until the program ends.

5. Memory

   • Virtual Memory: This type of memory is for when the computer runs out of available RAM and so uses part of the HDD (Hard Disk Drive) instead. This is not desirable however as the HDD is slower than just using RAM.
   • Flash Memory: This type of memory is solid state (i.e. No moving parts) that retains data even when power is removed. It is used in SSDs and memory cards, for example.

6. BIOS

   • Basic Input and Output System. This is the ROM chip on the motherboard that takes care of booting the OS into memory

7. Primary Storage

   • RAM
     • (Random Access Memory) is a device that can plug into the motherboard. RAM contains programs, instructions and data that are currently being worked on (in use)
   • ROM
     • (Read Only Memory) is usually a flash memory chip on the motherboard that contains instructions needed to start up (boot) the operating system
   • Sometimes called Main Memory. Refers to the memory areas that the CPU can access very quickly (Cache, RAM and ROM). Primary storage has the fastest read/write speeds and is mostly volatile.
   • cache
     • Sits between the CPU and RAM. Very fast. Holds frequently used data so that the processor doesn't have to keep going back and forth to the RAM.
     • Cache Size
       • Refers to how many frequently used instructions can be stored in the cache on the CPU.

8. Clock speed

   • Number of instructions that can be carried out in a second (Hz) - These days in Ghz (Billion)

9. Cores

   • How many individual processors (cores) are on a chip. The more cores, the more instructions can be done simultaneously.

10. Input

    • Device that transmits data into the computer so that it can be processed (e.g. buttons, gamepad, keyboard, microphone)

11. Output

    • Device that presents the results of processing to the user (e.g. screen, speakers, LED, Motor)

12. Software

    • The virtual (you can't touch them) programs or applications that a computer can run (e.g word processor, browser, file manager)

13. MAR

    • Holds memory address about to be used by the CPU

14. MDR

    • Holds data or instructions that have been fetched from memory

15. Program Counter

    • Holds the memory address of the instruction for each cycle

16. Accumulator

    • Stores the results of the calculations done by the ALU

17. ALU

    • Performs logical operations (AND, OR, NOT), Shift operations and Arithmetic operations (+,-, *, / )

18. CPU

    • Controls activities in the CPU (Such as flow of data between CPU and other parts) and makes FDE cycle happen in correct order

19. Embedded systems

    • A dedicated computer system built into another device (usually designed for a specific purpose) e.g. Dishwasher or microwave. Cheaper to produce and more efficient than general purpose computer.