The difference between SRAM and SDRAM

Source: Internet
Author: User



SDRAM (Synchronous dynamic random access memory), synchronous, refers to the memory work requires a step clock , The transmission of internal commands and the transfer of data are based on it, dynamic refers to the storage array needs to be constantly refreshed to ensure that the data is not lost, random refers to the data is not linear storage , but by the specified address to read and write data. The current 168-wire 64bit bandwidth memory basically uses SDRAM chip, operating voltage 3.3V voltage, access speed of up to 7.5ns, and Edo memory is the fastest 15ns. And the RAM with the CPU at the same clock frequency control, so that the RAM and CPU FSB synchronization, cancel the wait time, so its transmission rate than EDO dram faster.

sdram from development to now has gone through four generations of , namely: First generation SDR SDRAM, second generation DDR SDRAM, third generation DDR2 SDRAM, Fourth generation DDR3 SDRAM.
The first generation and the second generation SDRAM both use single-ended (single-ended) clock signals, and the third and fourth generation, due to their fast operating frequency, use a differential clock signal that can reduce interference as a synchronous clock. The clock frequency of the
SDR SDRAM is the frequency of data storage, and the first generation of memory is named after the clock frequency, such as pc100,pc133, which indicates that the clock signal is 100 or 133MHz, and the data read and write rate is 100 or 133MHz. The second, third, and four-generation DDR (Double data rate) memory is followed by the data read and write rates as a naming standard, and preceded by a symbol representing its DDR algebra, pc-is DDR,PC2=DDR2,PC3=DDR3. If the PC2700 is DDR333, its operating frequency is 333/2=166mhz,2700 to indicate a bandwidth of 2.7G. The
DDR reads and writes from DDR200 to DDR400,DDR2 from ddr2-400 to DDR2-800,DDR3 from ddr3-800 to ddr3-1666.
Many people interpret the SDRAM error as the first generation of SDR SDRAM, and as a noun interpretation, are misleading, SDR is not equal to SDRAM.

Pin: A metal pin used by a module or chip to connect to an external circuit circuit, while the module PIN is often said "golden finger" . The
Simm:sigle in-line memory Module, a single-column RAM module. Memory module is what we often say the memory, the so-called single-column refers to the module board and the motherboard socket interface only one row of pins (although both sides have gold fingers).
dimm:double in-line Memory module, dual-row RAM module. Is our common module type, the so-called dual-column refers to the interface between the module board and the motherboard slot has two pins, the module board on both sides of the gold finger corresponding to a row of pins.
rdimm:registered DIMM, dual-line memory module with register
So-dimm: Memory modules commonly used in notebooks.
Operating voltage:
SRAM is an abbreviation for English static RAM , which , DRAM memory of the same capacity can be designed as a smaller volume, but SRAM requires a lot of volume, so on the motherboard SRAM memory to occupy a portion of the area, on the motherboard which is SRAM?

One is placed between the CPU and main memory cache, it has two specifications: one is fixed on the motherboard cache memory, and the second is inserted in the card slot coast (cache on A Stick) extended cache, In addition, in the CMOS chip 1468L8 circuit, it also has a smaller capacity of 128 bytes SRAM, storing the configuration data we set.

another is to speed up the internal CPU data transmission, since 80486CPU, in the internal CPU is also designed to cache , so the Pentium CPU has so-called L1 cache (first-level cache) and L2cache (level two cache) nouns, General L1 Cache is built into the internal CPU, L2 cache is designed on the outside of the CPU, but Pentium Pro L1 and L2 cache at the same time designed in the internal CPU, so Pentium Pro is larger in size. The newest Pentium II also moves the L2 cache to a black box outside the CPU core.
SRAM obviously fast, do not need to refresh the action, but there are other shortcomings, is the high price, large volume, so on the motherboard can not be used as a large amount of main memory. Its characteristics are summarized as follows:

Advantages, fast speed, do not need to cooperate with the memory refresh circuit, can improve the overall efficiency.
Disadvantages, low integration, large power consumption, the same capacity is larger, and the price is high, a small amount of critical systems to improve efficiency.
System used by SRAM:
Cache between 0CPU and main memory
0CPU internal L1/L2 or external L2 cache
0CPU Coast cache for external expansion
0CMOS 146818 Chip (Rt&cmos SRAM)

SRAM vs. SDRAM comparison:

SRAM relies on a bistable trigger to memorize information, and SDRAM relies on the gate capacitance of a MOS circuit to memorize information. Since the charge on the capacitor leaks and needs to be replenished at regular intervals, the dynamic RAM needs to be set up with a refresh circuit. However, dynamic RAM is more integrated than static RAM, low power consumption, and thus low cost, suitable for large-capacity memory. Therefore, the main memory is usually SDRAM, while the buffer memory (cache) uses SRAM, at the access speed, Sram>sdram. In addition, memory is also used in devices such as video cards, sound cards, and CMOS to act as a device cache or to store fixed programs and data.

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The difference between SRAM and SDRAM

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