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All computer hardware, when you go beyond the surface, is another world. Random Access Memory (RAM) is no different. If one wants to write everything about RAMs, s/he will end up with tens of articles.
In this article, we will stick to the basics, as we did with the CPU and graphics cards.
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Random Access Memory
Random Access Memory is basically electronic circuitry that the computer uses as volatile storage, meaning that something is written on it, and deleted when power is shut off.. The written data need not to be in any order, meaning that all is “random”.
In modern RAMs, the data still remains on the circuit after the power off; it is not deleted immediately but “fadingly”. This makes computers susceptible to cold boot attacks, where an attacker having physical access to the computer can recover data that has not been deleted from the RAM. There is one particular case where RAM immersed into liquid nitrogen had data recovered from it about half an hour after power was disconnected (for details about cold boot attacks, you can check here.)
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Memory Clock and Input/Output Clock
Since there must be communication with the other parts of the computer, such as the CPU and the graphics card, RAM must operate at a certain frequency to enable this communication (input/output –I/O- frequency.)
The memory has a main clock, which is run at its own speed (DDR), doubled (DDR2), or quadrupled (DDR3), to get the IO clock.
These main clocks frequencies are 200, 266, 333, 400 or 533 Megahertz
If you do the math, I/O memory for DDR2 RAMs are two times of the memory clocks (400 / 200 = 2) whereas for DDR3 RAMs, they are four times (800 / 200). So, the DDR3 RAMs work twice fast as the DDR2 RAMs.
With the introduction of the Intel’s Bearlake platform (P35 platform) DDR3 RAMs began to receive more attention. With the Core i7 processors, which work only with DDR3 RAMs, DDR2 technology is underway to be history in the coming years. It was thought to be one the way out sooner, but the prices haven't come down enough yet, while DDR2 is now dirt cheap.
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DDR is actually an abbreviation. The whole is in fact DDR SDRAM, which stands for Double Data Rate Synchronous Dynamic Random Access Memory. All consumer computers, be they desktops, laptops or netbooks, use one of DDR, DDR2 or DDR3 memory.
As we have explained above, DDR2 and DDR3 RAMs differ with their memory and I/O clocks, as well as voltage and other electronic abitilies. However, they both have 240 pins to be connected to the motherboard, but you can not fit DDR2 RAM into a DDR3 slot, because the notches are in different places.That's good, since if you could put it in, it wouldn't work and might get damaged.
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Latency, as the word says, is the delay that occurs when the computer wants to access data on the RAM. As you will guess, the lower the latency the faster the hardware.
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The manufacturers employ different techniques that come out of their research and development departments to lower the latencies. The timings are stated as four integers, separated by dashes (such as 3-3-3-9). The order is CAS (Column Access Strobe) Latency, Row Address to Column Address Delay, Row Precharge Time and Row Active Time. As I mentioned above, the lower timings indicate lower latencies and thus faster RAM for a given clock speed. If you have narrowed your RAM selection after looking at price, speed, manufacturer reputation, warranty, and other terms, then finally check out the timings and choose the one that has lower values.
In the screenshot on the left, you see RAM running at 1067 Mhz, and with 7-7-7-20 timings.
Screenshot courtesy of HotHardware
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There are a quite a few RAM manufacturers worldwide that produce the highest quality RAMs; Kingston, OCZ, Corsair, Mushkin, Crucial, Buffalo and Twinmos to name a few. If you know what memory specifications to look for based on your computer's compatibility and needs, as well as your budget, you can't go wrong getting it from any of these brands.