Section 1.0 - Hardware


SubSection 1.6 - Memory Types, Characteristics, and their Purposes

Memory

  • The hardware component that stores data as the CPU works with it
  • The memory is commonly called RAM(Random Access Memory)
  • RAM is implemented as computer chips occasionally soldered to the circuit board, but more often attached to a specialized socket
  • Memory is different from storage drives:
    • Storage refers to the locations where data is held in the long term
    • Data in storage remains there when your computer is turned off
  • Importance of RAM
    • Performance- Having more RAM almost always leads to improved computer performance. If you have insufficient RAM, the CPU must work harder shuffling data between RAM and the page file
    • Software Support- Many applications require a minimum amount of RAM. Having less RAM can prevent you from running these applications, or it could perform so bad that it will be unpleasant to use.
  • Memory types can be classified in various ways:
    • Volatile Memory

      • Loses its contents when power isn't present
      • RAM is Volatile Memory
        • Its contents are lost when power is removed, even for a brief period
    • Non-Volatile Memory

      • Doesn't lose its contents when power is removed
  • Types of Memory

    • DRAM

      • Dynamic RAM
      • Older technology
      • Sends the row address and then sends the column address to access a cell
      • The CPU must repeat this process for every cell
      • DRAM must be refreshed hundreds of times per second
      • Circuits using DRAM must include the components necessary to refresh its contents
    • SRAM

      • Static RAM
      • Doesn't need to be refreshed
      • This memory holds its contents until power is removed
      • SRAM chips can be read more quickly than DRAM chips can
    • SDRAM

      • Synchronous DRAM
      • Synchronized with the system clock to improve performance
      • Internal interleaving enables overlapped accesses
      • Returns data from a memory cell in a single cycle of the system clock
      • Faster than ADRAM and keeps pace with the rest of your computer better
      • Most modern computers use SDRAM for system memory
      • Must be capable of operating at your system's bus speed
  • Types of Data Rates:

    • DDR
      Types of Data Rates
      Types of Data Rates

      • Double Data Rate
      • Doubles the transfer rate by transferring data on both the rise and fall of the clock signal
      • Data Transfer range of 200-400 MHz
      • DDR Memory modules transfer data on a bus that is 64 data bits wide
    • DDR2

      • Double Data Rate 2
      • Transfers data at a rate of 400-1066MHz
      • DDR2 Memory modules transfer data on a bus that is 64 data bits wide
    • DDR3

      • Double Data Rate 3
      • Transfers data at a rate of 800-1600MHz
      • DDR3 Memory modules transfer data on a bus that is 64 data bits wide
  • Parity vs. Non-Parity

    • Parity

      • A scheme that enables the detection of an error
      • A bit is added to ensure that the number of bits with the value one in a set of bits is even or odd
    • Non-Parity

      • Is regular memory
      • It contains exactly one bit of memory for every bit of data to be stored
  • ECC vs. Non-ECC (What's The Difference)

    • ECC

      • Error Correcting Code
      • Permits your computer not only to detect that an error has occurred, but also to correct that error
      • The computer can determine what was changed and what its original value was if it finds a error on it
    • Non-ECC

      • Doesn't correct errors on your computer
  • Single sided vs. Double Sided

    • Single Sided

      • Early memory packages featured DRAM chips on just one side
      • The chips are a single group that are used simultaneously
      • Much faster than double sided RAM
    • Double Sided

      • Has two groups of chips
      • The computers memory controller sees each of those two groups of chips separately
      • Can only read/write to one of them at a time
      • The controller must switch back and forth between chip groups
  • Single Channel vs. Dual Channel

    • Single Channel

      • Uses one 64-bit channel
    • Dual Channel

      • Doubles data throughout from the memory to the memory controller by using two 64-bit data channels, giving you a 128-bit data path
      • Requires both a dual-channel-capable motherboard and two or more DDR, DDR2, or DDR3 memory modules
      • Increases bandwidth
  • Speeds

    • PC100

      • Standard for internal removable computer RAM
      • PC100 refers to Synchronous DRAM operating at a clock frequency of 100 MHz, on a 64-bit wide bus, and a voltage of 3.3 V
      • Available in 168-Pin DIMM and 144-Pin SO-DIMM form factors
      • Backward Compatible with PC66 and was superseded by the PC133 standard
    • PC133

      • Computer Memory Standard
      • Refers to Synchronous DRAM
      • Operates
        • Clock Frequency of 133 MHz
        • 64-Bit Wide Bus
        • Voltage of 3.3 V
      • Available in 168 Pin DIMM and SO-DIMM form factors
      • Delivers a bandwidth of 1066 MB per second
      • Backward compatible with PC100 and PC66
    • PC2700

      • Standard name is DDR-333
      • Operates
        • Clock Frequency of 166 MHz
        • 64-Bit Wide Bus
        • Voltage of 3.3 V
    • PC3200

      • Other name for DDR-400
      • 3.2 GB per second Bandwidth
      • 200 MHz Bus Clock Speed