Weak current College】 【memory ddr1 and ddr2 difference.

The difference between DDR2 and DDR
Compared with DDR, DDR2 's major improvement is the same speed as the memory module, you can provide the equivalent of DDR memory twice the bandwidth. This mainly through in each device on the efficient use of both DRAM core. As a comparison, on each device DDR memory can only use a DRAM core. Technically, DDR2 memory is still only a DRAM core, but it can parallel access in each time you access handle 4 data instead of two.
DDR2 and DDR difference map
And double-speed operation of data buffering to DDR2 memory enables each clock cycle processing up to 4bit data, than the traditional DDR memory can handle high 2bit data has doubled. DDR2 memory is another improvement in that it uses the FBGA package replaces traditional TSOP.
However, despite the DRAM DDR2 memory core speed and DDR, but we still want to use a new motherboard to mix of DDR2 memory, DDR2 's physical specifications and DDR is not compatible. First, the interface is not the same, the number of pins to DDR2 240-pin DDR memory, 184-pin; Secondly, DDR2 memory of VDIMM voltage 1.8V, and DDR memory 2.5V different.
DDR2 is defined:
DDR2 SDRAM (DoubleDataRate2) is determined by the JEDEC (Joint Electron Device Engineering Council) for the development of new generation memory technology standards, it and the previous generation DDR memory technology standards, the biggest difference is that, although the same is used in the rising/falling clock extension for data transmission of basic, but DDR2 memory but with twice the previous generation DDR memory pre-fetch capability (i.e.: 4bit data pre-fetch). In other words, the DDR2 memory each clock can be 4 times the external bus speed read/write data, and to internal control bus 4 times the speed.
In addition, because the standards require all DDR2 DDR2 memory use FBGA package, which is different from the currently widely used in TSOP/TSOP-II package, FBGA package can provide more excellent electrical properties and thermal resistance, stability for DDR2 memory and future frequency of development provides a solid foundation. The evolution of DDR back, from the first generation to PCs DDR266, DDR333 DDR200 through to today's dual-channel DDR400 technology, first generation DDR's development has reached the limits of technology, has been very difficult to adopt practices to improve memory speed of work; with Intel's latest processor technology, FSB on memory bandwidth requirements are higher and higher, with higher and more stable operation frequency of DDR2 memory will be the trend of the times.
DDR2 and DDR differences:
In the understanding of the many new techniques of DDR2 memory, first let's look at a group of DDR and DDR2 technology comparison data.
1, latency issues:
As can be seen from the table above, in the same core frequency, the frequency of the actual work of DDR2 is twice the DDR. Thanks to DDR2 memory with twice the standard DDR memory 4BIT prefetch capability. In other words, although DDR2 and DDR, are rising in the clock and decrease deferred while extension for data transmission of basic, but DDR2 has twice the DDR of prefetch system command data. In other words, in the same 100 operating frequencies, the actual frequency of DDR 200MHz, but you can achieve 400MHz DDR2.
It also has another problem: in the same frequency of DDR and DDR2 memory, the latter's memory latency to slower than the former. For example, DDR200 and DDR2-400 with the same delay, which has twice the bandwidth. In fact, DDR2-400 and DDR400 has the same bandwidth, they are 3.2GB/s, but the core work of frequency DDR400 is 200MHz, and DDR2-400 core operating frequency is 100MHz, i.e. DDR2-400 delay than DDR400.
2. packaging and calorific value:
DDR2 memory technology, the biggest breakthrough in fact lies not in the users think twice the DDR of transmission capacity, but in a more low calorific capacity, lower power consumption, DDR2 can obtain faster frequencies increase, the breakthrough standard DDR 400 MHz limit.
DDR memory, usually in the form of TSOP chip package, the package can be a very good job in 200MHz, when more frequently, it is too long for the PIN may result in a high impedance and parasitic capacitance, which may affect its stability and frequency increase. This is a core frequency of DDR is very difficult to break through 275MHZ. While DDR2 memory uses the FBGA package. Different from the currently widely used in TSOP package, FBGA package provides better electrical performance and heat, steady for DDR2 memory and future frequency of development provides good protection.
DDR2 memory use .8V, relative to the DDR standard 2.5V, reduced, thereby providing significantly less power consumption and lower heat output, this change is significant.
DDR2 new technologies:
In addition to the above difference, DDR2 also introduces three new technologies, they are OCD, ODT and PostCAS.
OCD (Off-ChipDriver): it is the so-called offline-driven adjustment, you can improve by OCD DDRII signal integrity. DDRII by adjusting the pull-up (pull-up)/drop-down (pull-The resistance values down) so that both voltage equal. Use the OCD by reducing DQ-DQS tilt to improve signal integrity; by controlling the voltage to improve signal quality.
ODT: ODT is the built-in core of termination resistors. We know that use DDRSDRAM motherboard above in order to prevent the cable terminal reflected signal requires a large amount of termination resistors. It greatly increased the motherboard manufacturing costs. In fact, different memory modules on the final circuit requirements is not the same as the size of the termination resistor determines the cable signal ratio and reflectivity, termination resistors small cable signal reflection low but also a lower signal to noise ratio; termination resistor high, the cable-to-noise ratio, signal reflection. Thus the end resistance on the motherboard and is not a very good match memory module, but also to a certain extent affect the signal quality. DDR2 can based on your own characteristic built-in right of termination resistor, so you can ensure the best signal waveform. Use DDR2 motherboard not only reduces the cost, you get the best signal quality, this is a DDR cannot be compared.
PostCAS: it is intended to improve the efficient use of DDRII memory set. In PostCAS operation, the CAS signal (read/write command) can be inserted into the RAS signal behind a clock cycle, CAS command can additional delays (AdditiveLatency) remain valid. The original tRCD (RAS to CAS and delay) was AL (AdditiveLatency), AL can be 0, 1, 2, 3, 4. Because CAS signal on the RAS signal behind a clock cycle, therefore ACT and CAS signal will never produce a collision conflict.