What is the difference between RAM and SDRAM?

RAM Introduction

Random-Access Memory, a very important part of the computer's composition, is memory. The memory is a component used to store programs and data. For a computer, only memory is available to ensure normal operation. There are many types of memory, which can be divided into main memory and auxiliary memory [or internal memory and external memory] according to their use. The main memory is referred to as memory, and the memory plays a decisive role in the computer, and semiconductor memory cells are generally used. Because RAM is the most important memory in memory, we usually call it memory directly. Memory is where programs and data are stored. For example, when we use WPS to process a document, when you type a character on the keyboard, it is stored in memory. When you choose to save the data, the data in memory will be Store in a hard (magnetic) disk.

RAM can both read data from and write data. When the machine power is turned off, the data stored in it is lost. The memory modules that we usually buy or upgrade are used as the memory of the computer. The memory module (SIMM) is a small circuit board that puts together the RAM modules. It is inserted in the memory slot in the computer to reduce the RAM integration. The space occupied by the block. The memory bars currently on the market are 128M/bar, 256M/bar, 512M/bar and so on.

RAM category

According to the operating principle of the storage unit, the RAM is divided into static RAM and dynamic RAM.

Static RAM (SRAM)

The static storage unit is composed of a static trigger and an additional gate control. Therefore, it is relying on the self-protection function of the trigger to store data.

Dynamic Random Access Memory (DRAM)

The dynamic RAM memory matrix consists of dynamic MOS memory cells. The dynamic MOS memory cell uses the gate capacitance of the MOS transistor to store information, but since the capacitance of the gate capacitance is small and the leakage current cannot be absolutely equal to 0, the time for charge conservation is limited. In order to avoid the loss of stored information, the capacitor must be regularly added to the missing charge. This operation is often referred to as "refresh" or "regeneration," so that the DRAM has refresh control circuitry inside it, and its operation is also more complicated than static RAM. In spite of this, since the structure of a DRAM memory cell can be made very simple, using fewer components and low power consumption, it has become a mainstream product of large-capacity RAM.

RAM features

1, random access

The so-called "random access" refers to when the data in the memory is read or written, the time required is not related to the position of the information or the written position. In contrast, when reading or writing information from a sequential access (SequenTIal Access) storage device, the time and location it needs will depend. It is mainly used to store operating systems, various applications, data, and so on.

2, volatile

RAM cannot retain data when power is off. If you need to save data, you must write them to a long-term storage device (such as a hard disk). Compared with RAM and ROM, the biggest difference between the two is that the data stored in the RAM after the power is turned off will automatically disappear, and the ROM will not automatically disappear and can be stored for a long time.

3, sensitive to static electricity

Just like other fine integrated circuits, random access memory is very sensitive to the static charge of the environment. Static electricity can disturb the charge in the capacitor in the memory, causing data loss and even burning the circuit. Therefore, touch the metal ground before touching the random access memory.

4, access speed

Modern random access memory is the fastest among all access devices to write and read. Access latency is also negligible compared to other storage devices that involve mechanical operations.

5, need to refresh (regeneration)

Modern random access memories rely on capacitors to store data. After the capacitor is fully charged, it represents 1 (binary) and uncharged represents 0. Since the capacitor is more or less leaky, data will gradually be lost over time without special treatment. Refresh is the state of reading the capacitor for a specified period, and then recharging the capacitor according to its original state to make up for the lost charge. The need to refresh just explains the random access memory's volatility.

SDRAM Introduction

SDRAM Synchronous Dynamic Random Access Memory (Synchronous Dynamic Random Access Memory). Synchronous refers to the Memory work requires a step clock, internal command transmission and data transmission are based on it; dynamic refers to the storage array needs constant refresh to ensure The data is not lost; random means that the data is not stored linearly in turn, but is read and written by the specified address. The current 168-line 64-bit bandwidth memory basically uses SDRAM chips. The operating voltage is 3.3V, the access speed is 7.5ns, and the EDO memory is the fastest at 15ns. And RAM and CPU are controlled with the same clock frequency, make RAM and CPU FSB synchronize, cancel the waiting time, so its transmission rate is faster than EDO DRAM.

SDRAM has gone through four generations since its development. It is the first-generation SDR SDRAM, the second-generation DDR SDRAM, the third-generation DDR2 SDRAM, and the fourth-generation DDR3 SDRAM.

Both the first-generation and second-generation SDRAMs use single-ended clock signals. Because the third- and fourth-generation clocks have faster operating frequencies, differential clock signals that reduce interference are used as synchronous clocks.

SDR SDRAM clock frequency is the frequency of data storage, the first generation memory is named with the clock frequency, such as pc100, pc133 shows the clock signal is 100 or 133MHz, data read and write rate is also 100 or 133MHz.

The second, third, and fourth generation DDR (Double Data Rate) memory uses the data read/write rate as the naming standard, and is preceded by the symbol indicating its DDR generation. PC - DDR, PC2 = DDR2, PC3 = DDR3 . If PC2700 is DDR333, its operating frequency is 333/2=166MHz, 2700 indicates the bandwidth is 2.7G.

DDR read and write frequency from DDR200 to DDR400, DDR2 from DDR2-400 to DDR2-800, DDR3 from DDR3-800 to DDR3-1666.

Many people understand the SDRAM error as the first generation SDR SDRAM, and as a noun explanation, all are misleading. SDR does not equal SDRAM.

Pin: The metal pin used to connect the module or chip to the external circuit, and the pin of the module is often referred to as the “golden finger”.

SIMM: Sigle In-line Memory Module, single-bank memory module. The memory module is the memory module that we often say. The so-called single-row refers to the interface between the module circuit board and the motherboard slot. There is only one column of pins (although there are golden fingers on both sides).

DIMM: Double In-line Memory Module, dual-row memory module. Is our common type of module, the so-called double row refers to the module circuit board and the motherboard slot interface has two columns of pins, the module circuit board on both sides of the gold finger corresponding to a column of pins.

RDIMM: Registered DIMM, Registered Two-Wire Memory Module

SO-DIMM: A memory module commonly used in notebooks. Operating voltage: SDR: 3.3VDDR: 2.5VDDR2: 1.8VDDR3: 1.5V

What is the difference between RAM and SDRAM in ARM

The RAM includes SRAM and DRAM. The former is a static random access memory, which mainly relies on a flip-flop to store data without refresh, while the latter is a dynamic random access memory. Depending on the gate capacitance of the MOSFET, the data needs to be constantly refreshed to supplement the released charge. Since the data can be stored in a single pipe, the integration level can be higher, and the power consumption is also lower and more mainstream. It should be noted that because the refresh involves the charge and discharge process of the capacitor, the access speed of the DRAM is not as fast as the SRAM.

As for SDRAM, it is a type of DRAM that is a synchronous dynamic random access memory. Its working process requires the cooperation of synchronous clocks, so it is possible to avoid the influence of different route delays and avoid unstable states. Ordinary DRAM belongs to asynchronous transmission. When accessing data, it must wait for several clocks before operating (considering unsteady state), because it will take more time and affect the data transmission rate. With the constant increase of the clock frequency, the bottleneck will become more and more obvious, and the advantages of SDRAM will be better reflected.

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