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About Memory

About Memory

The discussion on Memory on this website is in context to the Computer Memory.

In computing, memory refers to the physical devices used to store computer programs (set of instructions) or data on a temporary or permanent basis for use in a computer or other digital electronic device. In computing, Random Access Memory (RAM) is referred to as primary memory, and secondary memory refers to the physical devices for program and data storage which are slow to access but offer higher memory capacity. When the intended content for primary memory is stored on secondary memory, it is called as use of 'virtual memory'.

Memory devices are normally addressable semiconductor devices consisting of silicon based transistors. There are two main types of semiconductor memory: Volatile and Non-volatile.

Examples of Non-volatile memory are Flash memory and ROM / PROM / EPROM / EEPROM memory. Flash memory can be used as primary and secondary computer memory, whereas ROM / PROM / EPROM / EEPROM are used for firmware such as to boot programs. Non-volatile memory can retain the stored information even when not powered.

Examples of Volatile memory are primary memory (typically dynamic RAM memory, DRAM), and fast CPU cache memory (typically static RAM memory, SRAM, which is fast but energy-consuming and offer lower memory capacity per area unit than DRAM). Volatile memory requires power to maintain the stored information. Most modern semiconductor volatile memory is either Static RAM or dynamic RAM (DRAM). SRAM and DRAM retain their contents as long as the power is connected and are easy to interface to.

Due to their structural simplicity, the DRAM can have very high densities (the amount of information bits that can be stored in the storage medium).

Dynamic random access memory is produced as integrated circuits (ICs) bonded and mounted into plastic packages with metal pins for connection to control signals and buses.

In early use individual DRAM ICs were used; later they were assembled into multi-chip plug-in modules (DIMMs, SIMMs, etc.). Some standard module types are:

  • DRAM chip (Integrated Circuit or IC)
  • Dual in-line Package (DIP) 16-pin
  • DRAM (memory) modules
    • Single In-line Pin Package (SIPP)
    • Single In-line Memory Module (SIMM)
      • 30-pin for FPRAM
      • 72-pin for EDO RAM and FPRAM
    • Dual In-line Memory Module (DIMM)
      • 168-pin for SDRAM
      • 184-pin for DDR SDRAM
      • 240-pin for DDR2 SDRAM/DDR3 SDRAM
  • Rambus In-line Memory Module (RIMM). Technically these are DIMMs but called RIMMs due to the proprietary slot.
    • 184-pin RDRAM
  • Small outline DIMM (SO-DIMM), about half the size of regular DIMMs, are mostly used in notebooks, small footprint PCs (such as Mini-ITX motherboards), upgradable office printers and networking hardware like routers. SO-DIMMs come in different versions:
    • 72-pin (32-bit)
    • 144-pin (64-bit) used for PC100/PC133 SDRAM
    • 200-pin (72-bit) used for DDR and DDR2
    • 204-pin (64-bit) used for DDR3
  • Small outline RIMM (SO-RIMM). Smaller version of the RIMM, used in laptops. Technically these are also SO-DIMMs but are called SO-RIMMs due to the proprietary slot.
 

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