The difference between the SDRAM and SRAM

SDRAM (Synchronous Dynamic Random Access Memory) Synchronous Dynamic Random Access Memory, need to be synchronized clock synchronization refers to the Memory work, internal commands and data transmission for sending on the basis of it, the Dynamic is refers to the storage array need to constantly refresh to ensure that data is not lost.Random is the order is not linear storage, but by the specified address for data reading and writing.At present most of the 168 line 64 - bit memory bandwidth is SDRAM chip, working voltage of 3.3 V voltage, access speed is as high as 7.5 ns, and fastest EDO memory of 15 ns.And RAM and CPU in the same clock frequency control, the RAM and CPU frequency synchronization, cancel the wait time, so the transfer rate is quicker than the EDO DRAM.

SDRAM from development to the present have gone through four generations, respectively is: the first generation of the SDR SDRAM, the second generation of DDR SDRAM, the third generation of DDR2 SDRAM, the fourth generation of DDR3 SDRAM.The first generation and second generation SDRAM adopts Single side (Single - Ended) the clock signal, the third generation and the fourth generation due to the working frequency is faster, so use can reduce the difference of interfering with the clock signal as a synchronous clock.

SDR SDRAM clock frequency is the frequency of data storage, the first generation of memory with clock frequency, such as the pc100, pc133 indicates the clock signal is 100 or 133 MHZ, read and write data rate to 100 or 133 MHZ.

Second, three, four generations of DDR (Double Data Rate) Data memory is used to read and write speed as naming standards, and said with the DDR algebraic symbols, PC - DDR, PC2 = DDR2, PC3 = DDR3.Such as PC2700 is DDR333, its working frequency is 333/2 = 166 MHZ, 2700 indicates the bandwidth of 2.7 G.

DDR, speaking, reading and writing frequency from DDR200 to DDR400 DDR2 from to DDR2 DDR2-400-400, DDR3 from DDR3-800 to DDR3-1666.A lot of people understand SDRAM wrong as the first generation of SDR SDRAM, and as a noun explanation, are misleading, the SDR is not equal to SDRAM.

SRAM

SRAM is the abbreviation of English StaTIc RAM, which is a kind of StaTIc access function of memory, do not need to refresh the circuit which can save it to internal storage data.Don't need to refresh as DRAM memory circuit, every once in a while, the fixed charge to DRAM refresh once, otherwise the internal data will disappear, so an SRAM has high performance, but an SRAM also has its disadvantages, namely its integration is lower, the same capacity of DRAM memory can be designed for smaller size, but it takes a lot of volume, SRAM and so on the motherboard SRAM memory takes up part of the area, which is an SRAM on the motherboard?

One is placed between the CPU and main Memory Cache, it has two types: one is fixed on the main board of the Cache (Cache Memory);2 it is inserted in the slot On the squadron (Cache On A STIck) expand with Cache, in addition in the circuit of CMOS chip 1468 l8, its internal also have smaller capacity 128 byte SRAM, storage we have set the configuration data.

Another kind is to speed up the CPU internal data transfer, since 80486 CPU, Cache is designed in the interior of the CPU is, therefore, in the PenTIum CPU is called the L1 Cache (level 1 Cache) and L2Cache (level 2 Cache) noun, general L1 Cache is built in the interior of the CPU, L2 Cache is a design on the outside of the CPU, but the PenTIum Pro L1 and L2 Cache design in the interior of the CPU at the same time, therefore, the size of PenTIum Pro.The latest Pentium II and L2 Cache to the CPU kernel black boxes outside.

Fast SRAM clearly, don't need to refresh action, but there are other faults, is the price is high, volume is big, so can't on the mainboard as a large amount of main memory.It now features summarized as follows:

Advantages: fast, don't need to cooperate with memory refresh circuit, can improve the overall efficiency.

Disadvantages: low level of integration, power consumption is bigger, the same capacity volume is larger, and the price is higher, a small amount for key systems to improve efficiency.

SRAM use system: between the CPU and main memory cache, CPU internal L1 / L2 or external L2 cache, external expansion with a squadron of CPU cache, CMOS chip 146818 (RT&CMOS SRAM).

　　

The comparison of SRAM and SDRAM:

SRAM memory by flip-flop information;SDRAM is to remember information by MOS gate capacitance in circuit.Due to the charge on the capacitor will leak, need time to complement, so dynamic RAM needs to set the refresh circuit.But dynamic RAM than static RAM, high integration, low power consumption and cost is low, suitable for mass storage.So the main memory is usually adopts the SDRAM, and use the SRAM Cache memory (Cache), on the access speed, SRAM SDRAM.In addition, the memory used in graphics card, sound card and CMOS device, is to act as equipment or save the fixed program and data cache.

 

 

keywords: SRAM