Dram,sram,sdram and Memory classification

The following content is from Wikipedia:

SRAM vs DRAM:

static random access memory (Static Random-Access MEmory, SRAM) is a random access memory one of them. The so-called "static" refers to this kind of memory as long as the power is maintained, the stored data can be kept constant. In contrast, the data stored in the dynamic random access memory (DRAM) needs to be updated periodically.

dynamic random access memory (Dynamic Random Access MEmory,DRAM) is a semiconductor memory, The main principle is to use the amount of storage charge in the capacitance to represent whether a binary bit (bit) is 1 or 0. Because the capacitance in the reality of the phenomenon of leakage, resulting in insufficient potential for memory loss, so unless the capacitance is often periodically charged, it will not ensure that the memory lasts. This is called "dynamic" memory because of the characteristics that require timed refreshes. Relatively speaking, "Static" Memory (SRAM) as long as the data is stored, even if not refreshed will not lose memory.

When the power supply stops, the data stored in DRAM and SRAM will still disappear (known as volatile memory), which is different from the ROM or flash memory that can store data after a power outage.

Sdram:

synchronous dynamic random access memory (synchronous dynamic random-access memory, referred to as SDRAM) is a dynamic random access memory (DRAM) with a synchronous interface. Typically, DRAM has an asynchronous interface so that it can respond to changes in control input at any time. The SDRAM has a synchronous interface that waits for a clock signal before responding to the control input, which synchronizes with the computer's system bus. The clock is used to drive a finite state machine, which carries out pipelining (Pipeline) operations on incoming instructions. This allows SDRAM to have a more complex operating mode than asynchronous DRAM (asynchronous DRAM) without a synchronous interface.

Pipelining means that the chip can accept a new instruction before it finishes processing the previous instruction. In a written pipeline, the write command executes immediately after the execution of another instruction without waiting for the data to be written to the storage queue. In a read pipeline, the required data arrives after a fixed number of clock frequencies after the read instruction is issued, and the waiting process can issue additional instructions. This delay is called the wait Time (Latency), which is an important parameter when purchasing a computer for storage.

SDRAM is widely used in computers, from the initial SDRAM to the subsequent generation of DDR (or DDR1), then DDR2 and DDR3 into the mass market, and is expected to start using ddr4,2017 year in the consumer market in 2014.

Memory

Computer Memory ( English:computermemory) is an electronic device that uses semiconductor technology to store data. The data of the electronic circuit is stored in a binary way, and each memory cell of the storage unit is called memory element.

The computer memory can be divided into the following two classes according to the relationship between storage capacity and power supply:

Volatile Memory

Volatile memory is the memory in which the data stored by the memory will disappear when the power supply is interrupted. There are mainly the following types:

• Random access memory (RAM)
  • Dynamic random access memory, English abbreviation writing dram, typically each unit consists of a transistor and a capacitor (the latter can be simulated with two transistors on an integrated circuit). The feature is that the unit occupies less resources and space, slower than SRAM, and needs to be refreshed. General computer memory is made up of DRAM. On a PC, DRAM appears as a memory stripe, with DRAM particles being 4-bit or 8-bit wide, and a single memory strip containing multiple particles with a bit width of 64 bits.
  • static random access memory , English abbreviation writing SRAM, usually each unit is composed of 6 transistors, but recently also appeared by 8 transistors composed of a SRAM unit. The feature is faster, but the unit occupies more resources than DRAM. The cache of the general CPU and GPU is comprised of SRAM.

non-volatile memory

Nonvolatile Storage (Non-volatile memory) means that the data stored by the memory does not disappear even if the power supply is interrupted, and the data in the memory can be read after the power is re-supplied. The main categories are as follows:

• Read-only memory (ROM)
  • Programmable read-only memory
  • Erasable Programmable read-only memory
  • Electronic erasure-type, reproducible, read-only memory
• Flash memory (for example: USB flash drive)
• Disk

Dram,sram,sdram and Memory classification