SDRAM, DDR, DDR2, DDR3, SODIMM, MicroDIMM, Pins, Timings and CAS Latency Made Easy!

You maybe feeling somewhat baffled by the various acronyms you see on websites selling laptop memory. Acronyms like SDRAM, DDR, DDR2, DDR3, SODIMM, MicroDIMM, pins and CAS Latency might be fine and dandy for all the computers gurus out there but what if you’re the 98% of us just out to upgrade your laptop and aren’t computer savvy? Well you know what, we hear you – in fact we’ll take action to prove it! While we can’t promise to make you a memory genius via what follows below, we do very much believe we can genuinely help. Ready to wipe some of that haze and get you on the right path to a successful laptop memory upgrade? Read on!


All the above, SDRAM, DDR, DDR2 and DDR3 are in themselves memory technologies. They differ in their age, speed, operating voltage and timings if to simplify things somewhat. Despite only SDRAM containing the RAM acronym, all are in fact RAM albeit of type SDRAM, DDR, DDR2 and DDR3. RAM in fact stands for Random Access Memory and is often used as an alternative to saying “memory”. You’re much more likely to see them written without the “RAM” component in their name but just remember that if you ever spot DDR RAM, DDR2 RAM or DDR3 RAM then it’s the exact same thing as DDR, DDR2 and DDR3. SDRAM is always written in a single form so if you ever see any source referencing SDRAM RAM then let’s just say whoever wrote it is a little keen on rewriting history.

Because SDRAM, DDR, DDR2 and DDR3 are all memory (or should we say RAM) technologies they are different too. You can’t go installing more than one type in your laptop as each has its own exclusive specification, including accompanying memory slots that are generally speaking in-compatible with the other types. Consequently, whatever your laptop (unless it’s older than circa 1997) it will only make use of one of the above. Have a DDR laptop? Install only DDR RAM. Have a DDR2 laptop? Only DDR2 RAM will work and so forth.


Now that you’re up to speed with memory technologies and a few other bits and pieces about laptop RAM then next in line is a SODIMM. Four different laptop memory types but only one SODIMM you ask? In short “yes”. You see, SODIMM stands for Single Outline Dual Inline Memory Module and is a rather elegant albeit technical way of saying the type card on which your memory arrives. Professionally speaking you would say a SODIMM is a type of PCB (Printed Circuit Board) rather than “card” but card is just as fitting.

A SODIMM being a PCB or card (no hurry deciding this for now) will contain SDRAM, DDR, DDR2 or DDR3 memory chips soldered onto it. Does this mean SODIMM’s vary depending on the memory type they feature? Yes, but don’t go rolling your eyes up just yet – it’s not as terrifying as you might think. While there are various differences, all you really should know is the number of pins (see below). The number of pins identifies the type of SODIMM. By knowing the number of pins the type of SODIMM your laptop requires contains, you can double check that you’re ordering the right type. Sometimes you may find some discrepancies in descriptions when buying so it certainly doesn’t hurt to do so.


If you’re more of a mobile mogul who often takes your laptop on travel then the chances are you actually own what’s known as a sub-notebook or netbook. Overall, we can classify these as types of small laptops. You’ve probably guessed what we plan to say next but just for consistency, a MicroDIMM is a miniature version of a SODIMM designed for small laptop computers, which just so happen to feature a more compact chassis. Not all sub-notebooks use MicroDIMM’s but don’t let that stop you remembering what they are.

Unless you own a sub-notebook or netbook then it’s suffice to say a MicroDIMM is not likely to be in your agenda. Even if you own a netbook, most aren’t upgradable so much the same applies there too. Perhaps the best advice is to keep in mind what a MicroDIMM is and also recall what we said about SODIMM pins above. The same theory can be applied to MicroDIMM pins – by noting the number of pins you can easily deduct the type of MicroDIMM.


We’ve spilled the beans about what SODIMM and MicroDIMM pins are above, which is in fact excellent because as a result we can immediately jump into defusing how many pins each of the different types of SODIMM’s and MicroDIMM’s (corresponding to each memory technology) contain.

If you’re ordering a SDRAM SODIMM laptop memory upgrade then you should expect a SODIMM with 144pins.

If however you need a DDR SODIMM laptop memory upgrade then it should contain 200pins.

And so we proceed onto a DDR2 SODIMM laptop memory upgrade. These also contain 200pins just as DDR SODIMM’s but rest assured they are incompatible with each other.

And finally (as of 2010) we have a DDR3 SODIMM laptop memory upgrade. These contain 204pins.

Things are a little dissimilar when it comes to MicroDIMM’s. If it’s a SDRAM MicroDIMM you need then the number of pins equals 144, the same as in a SDRAM SODIMM.

Meanwhile, if it’s a DDR MicroDIMM you need then this is 172pins.

Finally, should a DDR2 MIcroDIMM upgrade be on your agenda, these contain 214pins.


Each time you see or hear about timings (in the context of RAM) it’s all to do with the delays concerning how efficiently a given SODIMM or MicroDIMM operates. For simplicity’s sake this includes the delays associated with how fast a memory module can be accessed, find the data to be read or locate a free area to where to write some new data, copy data and refresh after performing any such commands.

Since timings influence the performance of a SODIMM or MicroDIMM, you will at times find that some memory manufacturers offer what we might reference as performance parts. These are standard SODIMM or MicroDIMM memory modules except for the trait that they’re certified to run stably at somewhat faster (tighter) memory timings.

Each type of memory technology, SDRAM, DDR, DDR2 and DDR3 operate in their own realm of timings. A SDRAM memory module will likely feature timings of 2-3-3-6, a DDR memory module 3-3-3-8, a DDR2 module 4-4-4-12 and a DDR3 module 7-7-7-20 respectively. Note that there are four numbers in each and that the newer the memory technology, the higher its timings.

While there is a small performance boost (circa 5%) to be gained from installing performance SODIMM’s or MicroDIMM’s you’re not prone to feel the difference even should you desire paying somewhat extra for the privilege. Nevertheless, if you do decide your laptop deserves nothing but the best then always remember to replace all the currently installed memory modules with new performance SODIMM’s or MicroDIMM’s. Failing to do so will cause your memory to run at the timings of the older module(s) thus wiping clean any performance benefit from installing your new RAM.

CAS Latency

The above deposition on timings wouldn’t be quite complete if we didn’t mention a few words on CAS latency, especially if you’ve taken the plunge and decided to purchase performance SODIMM or MicroDIMM’s after all.

When it comes to RAM timings, CAS latency is the one that has the most performance impact. CAS stands for Column Access Strobe and marks the delay that a SODIMM or MicroDIMM module must ensue prior to locating a given area within the memory. The CAS latency is usually marked as for example CAS 3, CL3, CL=3 or is hidden within the timings description as denoted above. For example, if you see a SODIMM or MicroDIMM with its timings written as 4-4-4-12 then the first number from the left (4 in this case) is the CAS latency. Similarly, if you find a DDR2 memory module of the same frequency but with timings of 3-4-4-10 then this means it’s been certified to run at a CL=3 instead of CL=4.


If you can muster the above then dare we say this outright but you’re already likely to know more about laptop RAM than most sales people in large computer chain stores. And they have a job their trying to selling you amongst others memory upgrades? Anyway, the focus is on you and not them, in fact it’s not even on you but instead on what you’ve just learned above.

You may not realise it but you actually deserve a sincere pat on your back. At first all the above acronyms may appear as hogwash but isn’t that just delusional? Take a deep breathe, follow the advice word for word and in spite of everything your fears might be telling you, buying a laptop memory upgrade will be a success!