Memory summary2

Memory can be divided into two categories according to the relationship between storage capacity and power supply:

Volatile memory refers to memory that is lost when the power supply is interrupted. There are mainly the following types:

  • RAM(Random access memory)
    • DRAM(Dynamic random access memory)
    • SRAM(Static random access memory)

Non-volatile memory refers to the memory stored in memory that is not lost when the power supply is interrupted. There are mainly the following types:

  • ROM(Read-only memory)
    • PROM(Programmable read-only memory)
    • EPROM(Erasable programmable read only memory)
    • EEPROM (Electrically erasable programmable read only memory)
  • Flash memory

According to the interface of the memory moudle, there are two kinds of common memory :

Single-In-line-Memory-Modules (SIMM) and Double Single-In-line-Memory-Modules (DIMM)


According to the work methods of the memory module :


Performance evaluation index of memory bar:

Storage capacity: the amount of binary information that can be accommodated by a single memory stick. For example, the storage capacity of the commonly used 168-wire storage bar is generally 32 trillion, 64 trillion and 128 megabytes.

Access speed: the shortest time required between two separate access operations, also known as the storage cycle, and the access cycle of the semiconductor memory is generally 60 nanoseconds to 100 nanoseconds.

The reliability of memory: the reliability of the memory is measured by mean time between failures, which can be understood as the mean time interval between two failures.

Performance ratio: performance mainly includes memory capacity, storage period and reliability. Performance ratio is a comprehensive index, which has different requirements for different storage.

SDR and DDR1/2/3:

single-sided and double-sided、single-rank and double-rank

If the 9 chips of 1 ECC DIMM are all on the same side of DIMM, it is called single-sided. If nine chips are distributed on both sides of the DIMM, it is called double-sided. As a supplement to single-sided and double-sided, DIMM is also divided into single-rank and double-rank (i.e., 1R, 2R, which we often see on lable in memory).

2R*8– R is rank,8 is the memory particle bit width; When the particle size is equal to 64bits, this module has a RANK.

References   内存频率介绍 single-sided/double-sided/single-rank/double-rank rank数的计算 内存 bank 和rank 区别