Selecting the Correct Laptop Memory Upgrade

Perhaps the most difficult part of performing a laptop memory upgrade is finding the proper type of memory for your specific laptop. Since this can be a complicated subject and often requires some research up front, let us look at a few of the most important aspects of laptop memory modules so you can better understand the key points of selecting your laptop memory.

Form Factor

Laptop memory comes in different form factors. The most common are SO-DIMM (small outline DIMM), others like SIMM (single inline memory module), DIMM (double inline memory module) were used in first generation laptops, but have not been used in years. SO-DIMMs are most often used in laptops as they are smaller than standard DIMM modules used in desktop computers. SO-DIMMs are usually 2.6 inches long and 1.25 inches in height. The smallest module available is the Micro-DIMM; these are very small modules only measuring about an inch wide and are used in high end ultra portable laptops.

Memory Type

In addition to the different form factors, memory is categorized into standards. The most common are DDR, DDR2, and DDR3. All DDR Memory operates in a similar manner as it transfers data on the rise and fall of each clock cycle; effectively doubling the transfer speed of older SDRAM technologies. Each increment represents an improvement in transfer speeds and latency. In some cases these standards are backwards-compatible, but not always. DDR is the first generation of Double Data Rate memory, and is the slowest of the DDR Standards; it is usually packaged in a 200 pin SO-DIMM form factor and runs at speeds of 266 MHz – 400 MHz. DDR2 memory is the second generation of DDR memory, it increases speeds to between 400 MHz and 800 MHz and are packaged in a 200 pin SO-DIMM form factor. The latest and greatest in laptop memory is DDR3; it is available in speeds of 800 MHz – 1600 MHz and comes in a 204 pin SO-DIMM package. DDR3 memory further reduces the operating voltage of DDR2 to a lower 1.5 Volts, offering a slight improvement in battery life.

Transfer Speeds

The speed rating for memory refers to the “clock speed” which is the rate at which the memory can send and receive data. As mentioned previously, DDR modules have clock speeds from 266 MHz to 400 MHz, DDR2 ranges between 400 MHz and 800 MHz, and DDR3 runs between 800 MHz and 1600 MHz. While a higher clock speed is usually better, one important rule to remember is that if you are adding memory alongside existing memory, no matter how fast the transfer speed is on the new memory, it will only run as fast as the old memory since all the RAM in the system has to operate at the same speed.

Pin Configuration

The number of pins and their configuration vary between types. It is important to match the memory type specifically to your laptop. The pin configuration is typically a product of the type of memory being utilized. DDR and DDR2 memory both use a 200 pin configuration for the modules, where DDR2 has a slightly different keying on the module, this helps avoid users trying to install memory into the wrong type of memory slot. Still care must be taken because the difference is very minor and to the naked eye may look the same. DDR3 use a 204 pin module which is the same physical size as DDR and DDR2, but has the key notch further towards the middle of the module.


Latency is the delay in time from when a memory controller tells the RAM module to access an explicit memory column. This delay is measured in clock cycles for most types of modules. The lower the number the better, but as with memory speed, all modules installed will run at the same latency no matter what their specific rating, so buying ultra low latency RAM and installing it with higher latency RAM will not take full advantage of the low latency RAM.


Different standards also run on different voltages. First generation DDR memory runs at 2.5 Volts however DDR2 memory operates at a lower voltage of 1.8 Volts and thus improves on laptop battery life in most instances. The latest DDR3 memory runs at 1.5 Volts offering improved battery life over DDR and DDR2 memory. In general if you get the right memory type, be it DDR, DDR2 or DDR3, it will be the right voltage as the voltage is part of the standard for the module. As the memory types evolved, they began to use lower and lower voltages to operate the RAM memory which has helped curb the energy appetite of laptop computers.

As you can see, there is a lot to consider when selecting the correct memory for your laptop. If you are adding memory to your machine, you will need to know the specifications of the memory that is already installed in your machine, in order to get the correct memory. If you are replacing the memory, you only need to be concerned about what memory is compatible with the machine. Luckily, Spare Parts Warehouse has a wide selection of memory and easy to use tools to help you find the right memory upgrade for your laptop.