1.0 PC Hardware

1.3 Compare and contrast RAM types and features.

Memory types have changed through the years, driven by standardization and technology. It is one of the most important components of your computer, but differs somewhat with each motherboard.

  • Types

    • DDR

      Double data rate is a type of SDRAM in which data is sent on both the rise and fall of the clock cycle.

      • Twice as fast as SDRAM
      • Also refered to as "Double Pumping"
      • 2.5 volts
      • 184 pins

    • DDR2

      • Twice as fast as DDR
      • 240 pin DIMM

    • DDR3

      • Four times as fast as DDR
      • 240 pin DIMM

    • SDRAM

      • Synchronized Dynamic Random Access Memory
      • Runs on clock speeds
      • 3.3 volts
      • 168 pins

    • SODIMM

      SODIMMs (Small Outline Memory Modules) are a smaller alternative to a DIMM, being roughly half the size (68mm x 32mm) of regular DIMMs. SO-DIMMS are commonly used in systems which have space restrictions such as notebooks, small footprint PCs, high-end upgradable office printers, and networking hardware like routers.

      • 72-pin slots - 32-bit data path, now obsolete
      • 100-pin slots - 32-bit data path, two notches
      • 144-pin slots - 64-bit data path, single notch near the center
      • 200-pin slots - 64-bit data path, single notch nearer to one side
      • 204-pin slots - 64-bit data path, single notch nearer to one side

    • RAMBUS

      Rambus In-line Memory Module (RIMM) slots were first introduced as a proprietary standard on the Intel Pentium 3 motherboard by Rambus, Inc. in the mid 1990s, but the technology quickly fell from favor as a result of the higher expense.

      Rambus Dynamic Random Access Memory (RDRAM) modules are double data rate memory, transfering data on both the rising and falling of the clock cycle and measured 133mm x 35mm in size with a 16-bit, 184 pin and a 32-bit, 232 pin form factor.

      Computers that support RIMM require all of the memory slots to be filled. Empty slots must be filled with either another RIMM module or a Continuity RIMM (C-RIMM) pass through module for 16-bit systems or a Continuity and Termination RIMM (CT-RIMM) for a 32-bit system to allow a continuous signal.

    • DIMM

      Dual In-line Memory Modules began to replace SIMMs (single in-line memory modules) as the predominant type of memory module as Intel's Pentium processors began to gain in popularity. The primary difference between SIMMs and DIMMs is that DIMMs have separate electrical contacts on each side of the module, while opposing contacts on SIMMs are connected. Standard DIMMs have a 64-bit data path and come in three common pin configurations.

      • 168-pin slots - for SDRAM memory commonly found in Pentium and Athlon systems
      • 184-pin slots - for DDR SDRAM memory for desktop computers
      • 240-pin slots - for DDR2 and DDR3 SDRAM memory for desktop computers

      SDRAM modules have two notches on the bottom edge, DDR SDRAM modules have one.

    • Parity

      • Uses an additional chip for parity
      • Higher cost due to additional chips
      • Cannot correct, but can detect errors

    • Non-parity

      • Has fewer chips
      • Does not need to calculate parity
      • Non-parity systems have no fault tolerance

    • ECC

      • Error Correcting Code
      • Capable of detecting and correcting errors
      • Used in high-end systems
      • Motherboard must support ECC

    • Non-ECC

      • Is not capable of correcting errors

    • RAM configurations

      • Single channel

        • Memory controller can only access one module at a time

      • Dual channel

        • Requires a motherboard capable of dual-channel technology
        • Requires two or more memory modules
        • Best to use identical pairs of memory modules
        • Memory banks are typically color-coded

      • Triple channel

    • Single sided

      Refers to a single rank of chips in which the computer can access all at once.

    • Double sided

      • A type of memory in which its chips are divided into two ranks
      • Only one rank can be accessed at a time
      • Access must switch from one rank to the other and back again

  • RAM compatibility and speed


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