DDR = Double Data Rate double rate, DDR SDRAM = double rate synchronous dynamic random access memory, people are commonly known as DDR, where SDRAM is the abbreviation of Synchronous Dynamic Random Access Memory, that is, synchronous dynamic random access memory. DDR SDRAM is the abbreviation of Double Data Rate SDRAM, which means double rate synchronous dynamic random access memory. DDR memory is developed on the basis of SDRAM memory, and the SDRAM production system is still used. Therefore, for memory manufacturers, only a slight improvement on the equipment for manufacturing ordinary SDRAM can realize the production of DDR memory, which can effectively reduce cost.
Double data rate synchronous dynamic random access memory (English: Double Data Rate Synchronous Dynamic Random Access Memory, referred to as DDR SDRAM) is SDRAM with double data transfer rate, its data transmission speed is twice the system clock frequency, due to the speed Increase, its transmission performance is better than traditional SDRAM.
DDR SDRAM can transmit data on both the rising and falling edges of the system clock.
JEDEC establishes speed specifications for DDR memory, and is divided into the following two parts: classified by memory chip and classified by memory module.
SDRAM only transmits data once in a clock cycle, it transmits data during the rising period of the clock; and DDR transmits data twice during a clock cycle, that is, transmits data once during the rising and falling periods of the clock.
There are big design differences between DDR SDRAMs, and different clock frequencies are designed. For example, PC-1600 is designed to run at 100 MHz, while PC-2100 is designed to run at 133 MHz.
The DDR SDRAM module is used in desktop computers and is called DIMMs. It has 184 pins (instead of 168-pin SDRAM, or 240-pin DDR2 SDRAM), and can be distinguished from the number of different notches (DDR SDRAM, there is one, SDRAM , There are two SDRAM DIMMs). SO-DIMMs of DDR SDRAM on notebook computers have 200 pins, and the same number of DDR2 SO-DIMMs. The gaps of these two specifications are also very similar, if you can not determine the correct match, you must insert carefully.
Memory chip
DDR-200: DDR-SDRAM memory chip runs at 100MHz
DDR-266: DDR-SDRAM memory chip runs at 133MHz
DDR-333: DDR-SDRAM memory chip runs at 166MHz
DDR-400: DDR-SDRAM memory chip runs at 200MHz (the highest DDR specification set by JEDEC)
DDR-500: DDR-SDRAM memory chip runs at 250MHz (non-JEDEC DDR specification)
DDR-600: DDR-SDRAM memory chip runs at 300MHz (non-JEDEC DDR specifications)
DDR-700: DDR-SDRAM memory chip runs at 350MHz (non-JEDEC DDR specification)
Chip module
In order to increase the memory capacity and bandwidth, the chip will use the combination of modules. For example, the 64-bit bus about DIMMs requires eight 8-bit chips to be processed concurrently. Multiple chips with common address lines are called memory rank. This term was introduced to avoid confusion with the row and bank inside the chip.
PC-1600 memory {module} refers to a DDR-200 memory chip operating at 100MHz, which has a bandwidth of 1.600GB/s
PC-2100 memory module refers to a DDR-266 memory chip operating at 133MHz, which has a bandwidth of 2.133GB/s
PC-2700 memory module refers to a DDR-333 memory chip operating at 166MHz, which has a bandwidth of 2.667GB/s
PC-3200 memory module refers to a DDR-400 memory chip operating at 200MHz, which has a bandwidth of 3.200GB/s
The PC3200 is designed using a DDR-400 chip with a bandwidth of 3200 MB/s. At 200 MHz of DDR SDRAM, due to the data transfer of the rising and falling clock edges of the PC3200 memory, its effective clock rate is 400 MHz.
(DDR1) has been replaced by DDR2 SDRAM, with some modifications to allow higher clock frequencies. The competition with DDR2 is Rambus XDR DRAM. DDR3 SDRAM is a new standard that provides higher performance and new functions.
DDR prefetch buffer (prefetch buffer) depth is 2 bits, while DDR2 uses 4 bits. Although the clock rate of DDR2 is higher than DDR, the overall performance has not improved, mainly due to the high latency of DDR2. DDR2 did not improve significantly until 2004.
MDDR is an abbreviation of Mobile DDR, which is used in some mobile electronic devices, such as mobile phones, handheld devices, digital audio players, etc. By including reduced power supply voltage and advanced refresh options (advanced refresh options) technology, MDDR can achieve higher power efficiency.
Using the following formula, you can calculate the DDR SDRAM clock frequency.
DDRI/II memory operation clock frequency: actual clock frequency*2. (Since the two data are transmitted simultaneously, the clock frequency of the 200MHz memory will operate at 400MHz.)
Memory bandwidth = memory speed * 8Byte
Standard formula: memory division factor = clock frequency/200→*speed algorithm: external frequency* (division frequency/synchronization frequency) (using this formula will result in a 4% error).
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