1.2 Memory

1.2 Memory

1. Virtual Memory

   • Located on the hard disk
   • used when there is to much memory in the ram
   • Simulated memory on the Hard Drive
   • Disk thrashing - occurs when a computer's virtual memory subsystem is in a constant state of paging, rapidly exchanging data in memory for data on disk

2. RAM

   • Stands for random access memory
   • Located on the MotherBoard
   • Directly accessible by the processor
   • Holds the data/instructions that are currently in use by the processor
   • All data/instructions are lost once power is turned off
   • Very expensive

3. ROM

   • Instructions are permanently etched onto a ROM chip
   • When power is turned off, All instructions remain on the ROM chip
   • Bootstrap Loader is held in ROM

4. Flash Memory

   • USB Flash Drive
   • USB
   • Solid State
   • Non - Volatile
   • EEPROM
   • Can be electronically erased

5. Registers

   • A register may hold an instruction, a storage address, or any kind of data
   • Some instructions specify registers as part of the instruction.
   • A processor register (CPU register) is one of a small set of data holding places that are part of the computer processor.

6. Cache

   • To be cost-effective and to enable efficient use of data, caches must be relatively small. Nevertheless, caches have proven themselves in many areas of computing because access patterns in typical computer applications exhibit the locality of reference.
   • Moreover, access patterns exhibit temporal locality if data is requested again that has been recently requested already, while spatial locality refers to requests for data physically stored close to data that has been already requested.
   • In computing, a cache is a hardware or software component that stores data so future requests for that data can be served faster; the data stored in a cache might be the result of an earlier computation, or the duplicate of data stored elsewhere.

7. Solid State

   • An all-electronic storage device that is an alternative to a hard disk.
   • Employed in myriad products, including mobile devices, iPods, cameras, laptops and desktop computers,
   • solid state drives (SSDs) are faster than hard disks because there is zero latency (no read/write head to move).

8. Cores

   • A set of instructions can allow a software program perform a specific function. Processors can have a single core or multiple cores. A processor with two cores is called a dual-core processor and four cores is called a quad-core processor.
   • A quad-core processor is a chip with four independent units called cores that read and execute central processing unit (CPU) instructions such as add, move data, and branch. Within the chip, each core operates in conjunction with other circuits such as cache, memory management, and input/output (I/O) ports.
   • A core is usually the basic computation unit of the CPU - it can run a single program context (or multiple ones if it supports hardware threads such as hyperthreading on Intel CPUs), maintaining the correct program state, registers, and correct execution order
   • A processor [layman's terms] is a physical manifestation of one or more "cores" as an IC. The "cores" , technically speaking processors themselves and are independent of each other. When we say a quad core processor , we mean that a single chip processor has 4 cores , which are 4 computing elements.

9. Dynamic RAM

   • Dynamic random-access memory (DRAM) is a type of random access semiconductor memory that stores each bit of data in a separate tiny capacitor within an integrated circuit. The capacitor can either be charged or discharged; these two states are taken to represent the two values of a bit, conventionally called 0 and 1. The electric charge on the capacitors slowly leaks off, so without intervention the data on the chip would soon be lost
   • DRAM requires an external memory refresh circuit which periodically rewrites the data in the capacitors, restoring them to their original charge.
   • dynamic memory as opposed to static random-access memory (SRAM) which does not require data to be refreshed. Unlike flash memory, DRAM is volatile memory (vs. non-volatile memory), since it loses its data quickly when power is removed. However, DRAM does exhibit limited data remanence.

10. SRAM

    • Static random-access memory (static RAM or SRAM) is a type of semiconductor memory that uses bistable latching circuitry (flip-flop) to store each bit.
    • SRAM exhibits data remanence, but it is still volatile in the conventional sense that data is eventually lost when the memory is not powered.
    • The term static differentiates SRAM from DRAM (dynamic random-access memory) which must be periodically refreshed. SRAM is faster and more expensive than DRAM; it is typically used for CPU cache while DRAM is used for a computer's main memory.

11. MDR Memory

    • Memory Data Register
    • Is the register of a computers control unit

12. Processor

    • Performs calculations in the computer - Executes Instructions

13. MAR

    • Memory address register
    • It is the CPU Register that stores either the memory address from witch data will be fetched or the address from which data will be sent and stored