Introduction
The memories DDR3 (Double Data Rate 3) arrived in the market to replace the standard DDR2, such as this replaced the DDR type. The motivation of this change it is, as always, the need for better performance. In this article, you will see the main features of DDR3 memory and will know your differences in relation to the the previous standards.
The main features of the DDR3 memory
The memories DDR stand out in relation to the previous pattern – memories the SDR SDRAM – because they are able to perform two operations of read or write per clock cycle (in a few words, the speed with which the processor prompts for operations – learn more in this article about processors). The memories DDR2, in turn, double that capacity, performing four operations per clock cycle.
Type DDR3 follows the same path: it doubles the amount of operations by time relation to the previous pattern, that is, done 8 procedures read or write the each clock cycle, four at the beginning of this and the other four in the end.
To better understand this aspect, consider that, when we refer to the clock cycle, we are dealing withthe communication of the memory with the outside. However, the memory works with a frequency own internally.
Taking this characteristic into account, the more the question of the operations per clock cycle, we have the following scenario:
– A module DDR-400, for example, operates internally at 200 MHz, but it offers a 400 MHz by working with two operations per cycle (2 x 200);
– A stick of DDR2-800, which also works internally to 200 MHz, can offer the 800 MHz, which is four operations at a time (4 x 200).
– Following the same logic, we can take the example of a module DDR3-1600 that it, like the previous, it works internally to 200 MHz, however, by use of 8 operations per clock cycle, can offer up to 1,600 MHz (8 x 200).
Worth mentioning that, in general terms, the rates of frequency of communication external are four times larger than the internal clock. With this is a module that work internally at 200 MHz works externally at 800 MHz, for example.
There is, however, an aspect of the where DDR3 memory takes disadvantage: latency, in a few words, the time that memory takes to provide a given requested. The smaller this number, the better. Here are the rates more common for each type of memory:
– DDR: 2, 2.5 and 3 clock cycles;
– DDR2: 3, 4, and 5 clock cycles;
– DDR3: 7, 6, 8, or 9 clock cycles.
Note that, with this, a module DDR2 can spend up to 5 clock cycles to begin to provide a given, while in the type DDR3 this range can be up to 9 cycles.
To be able to decrease the latency, the manufacturers make use of several features in the modules DDR3, as a mechanism of calibration of the electrical signal, which provides greater stability in the transmissions.
With regard to energy consumption, the DDR3 memory can take advantage in relation to the technologies previous: by default, work with a 1.5 V vs. 1.7 V and 2.5 V of the types DDR2 and DDR, respectively. It is important to highlight, in the note, however, that these values may be increased slightly by the manufacturer to meet certain needs – to achieve a certain level of clock, for example.
Dual-Channel and Triple-Channel
As with its predecessors, the modules DDR3 can also work with the scheme to Dual-Channel, where the controller causes the memories to transfer twice as much data per cycle: time 64-bit, 128-bit.
But, from the line of Intel Core i7 processors, DDR3 memory now have a new mode: Triple-Channel. As the name indicates, in this mode, the memories can now work with the triple data per cycle. Thus, if each channel transmits 64-bit, we have so a total of 192 bits per time. In addition, if in Dual-Channel is necessary to use two memory sticks with the same specifications, in Triple-Channel there are three necessary. This indicates that the the motherboard needs to count not only with a chipset is compatible (the same goes for the processor) as also has more memory slots, making such devices more expensive to the user.
In the same way that it is possible to find kits with combs memory for Dual-Channel, there are manufacturers providing kits for Triple-Channel.
The physical aspects of the DDR3 memory
As well as the memories DDR and DDR2, the DDR3 feature with a slot, that is, with a small division between its terminals contact. To avoid confusion between the standards, each type has this space in a different position. In the case of DDR3, the notch is more to the left. The image below shows a comparison between the three types:
The DDR3 memory will follow the example of the type DDR2: usually are found with chips that use the tunnel CSP (Chip Scale Package) with fittings FBGA (Fine-pitch Ball Grid Array), whose main feature it is the fact of the terminals of the chip being small welds. The advantage of this is that the electrical signal flows more easily and there is less chance of physical damage. The DDR memory, in turn, is often found in the tunnel TSOP (Thin Small Outline Package). Learn more about this in the article Memories ROM and RAM.
The number of contacts of the modules DDR3 is also the same combs DDR2: 240. The type DDR has 184.
On-Die Termination (ODT)
This is more of a point where the DDR3 are similar the default DDR2: both work with a feature called On-Die Termination (ODT). This is a technology that helps prevent transmission errors. How?
The electrical signals suffer an effect return when you reach the end of a path transmission. Roughly speaking, it is as if the power knocked on the wall at the end of your path and come back. By various reasons, this effect can also occur in the “middle of the path”. In the case of memories, this problem, known as “signal reflection”, it can mean a loss of performance and the need for retransmission of data.
In the memories DDR, this problem is handled by through a method that reduces signal reflection from of resistors that are added to the motherboard. This is the device that comes the name”termination resistive”.
Technologies, DDR2 and DDR3, the termination resistive on the motherboard not proved to be efficient, due to the characteristics physical of these types of memory. On this problem, it was necessary to study alternatives and then came the ODT. In this technology, the termination resistive lies within the own memory chip. With this, the path traversed by the signal is smaller and there is less noise, that is, less loss of data. To the motherboard ends up benefiting from this technology, as a component stops to be added, reducing costs of production.
Nomenclature of DDR3 memory
Like its predecessors, the DDR3 following two denominations: DDR3-XXXX and PC3-YYYY, where YYYY indicates the amount of megabytes transferred per second (value the theoretical maximum). The following table shows the specifications the most common:
Missed to explain the meaning of XXXX, it is not the same? This number does allusion to a measure known as the mega transfer – in our case, mega transfer per second, that is, MT/s, which informs the amount of data transferred at a time. Thus, a module DDR3-800 indicates that the dispotivos works with up to 800 million data transfer per second.
Ending
DDR, DDR2 and now DDR3. So much variation makes part of the constant need that the industry has to offer technologies that can keep up with the growing power of the processors. This indicates that a new standard, perhaps the DDR4 is coming? Can make sure that yes. Companies such as Intel and organizations such as JEDEC already work on the specifications of the new memories that may be not only more fast, but also feasible in terms cost and energy consumption.
