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Notebook Memory Guide Part 3 of 4

Memory Types & Money Saving Tips

You probably know how much notebook memory (or RAM) your system has. But do you know what type of memory it is?

It is important to know this information especially when your notebook starts to slow down under the weight of multitasking.

Knowing the type of RAM your notebook has is the first step to upgrading your notebook's memory and improving the performance of your system.

Just going to a computer store and saying, "I need more RAM" may lead you nowhere. You may end up buying memory modules that are incompatible with your notebook.

In part 4 of this memory guide, we will provide a tutorial on upgrading laptop memory. But for now, get familiar with the basics on notebook memory types.

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Notebook Memory Modules

Memory technologies change rapidly and as such, there are many different types of memory products on the market. But these memory products are not always compatible with each other.

The memory you purchase will come in the form of memory modules, which are made up of memory chips and printed circuit board (PCBs).

Desktop computers use Dual Inline Memory Module (DIMMs); "dual" indicates that the module has pins on both of its sides. The total number of pins on a DIMM is typically 240, but it could also be 168 or 184.

Because of the smaller size of laptop/notebooks, they possess Small Outline DIMMs (SO-DIMMs). These are approximately half the length of regular DIMMs. SO-DIMMs typically have 200 pins (100 on each side) but they can also have 144, 172 and 240 pins as well.

See below to familiarize yourself with the look of DIMM and SO-DIMM. Notice the differences in length and the silver and rust-colored pins on the edges of the DIMM and SO-DIMM respectively. Those pins connect the module to the laptop.




so-dimm memory module

Memory module types and indeed the number of modules supported vary by laptop. Therefore, it is very important that you know what memory your laptop support before you actually purchase a memory upgrade.

Below, we breakdown SO-DIMM according to memory types.

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Notebook Memory Types

Synchronous Dynamic Random Access Memory (SDRAM)

SDRAM (synchronous dynamic random access memory) are typically 144-pin SO-DIMMs as pictured below. It waits for a clock signal before transferring data and hence it is synchronized with your notebook's system bus.

This module provides a markedly improved performance over asynchronous DRAM. However, with the advances in RAM technology, most newer notebooks no longer use SDRAM.

DDR SDRAM (DDR means Double Data Rate)

DDR SDRAM sends and receives data twice as fast as standard SDRAM. DDR memory typically comes in the form of a 200-pin DDR SO-DIMM but it also comes in 172-pin DDR MICRO DIMM. The latter is typically used exclusively in ultraportables and periodically in thin-and-lights laptops.

DDR2 SDRAM (Double Data Rate Synchronous Dynamic Random-Access Memory)

DDR2 SDRAM is yet another upgrade to the original SDRAM idea. This second generation DDR memory provides improved bandwidth and draws less power from the battery. DDR2 modules can be purchased in the popular 200 pin or 240 pin types.

Memory Speed

Prior to upgrading memory, it is useful to know the basics on memory speed. Two factors are used to determine speed; the first is operating frequency /clock speed and secondly, the bandwidth.

The way memory speed is written is different between the memory types.

SDRAM is memory speed is denoted as PCyyy; for example PC100 and PC133. SDRAM rated PC100 and PC133 work at 100MHz and 133MHz and provide 800MB/s and 1066MB/s bandwidth respectively.

However DDR, DDR2 and DDR3 are generally denoted as DDRxxx/PCyyyy. The letters indicate the memory type and the first number tells you the highest clock speed that the memory chip can support. Therefore, DDR266 means that the memory can support a maximum of 266MHz.

In some cases, the memory type is denoted as DDRx xxx as is the case with DDR3 1066. In this case, the first set of characters (DDR3) indicate the memory type.

Bear in mind that the labeled clock rating is not the real clock rating. The real clock rate of the DDR, DDR2 or DDR3 memory is half of the labeled clock speed. Therefore DDR3-1333 memory will have a real clock rate of 666 MHz.

When reading memory specifications, the second number in the DDRxxx/PCyyyy format classifies the memory module. It tells you the maximum transfer rate that the memory reaches, in MB/s.

For example, DDR266 provides 2100MB/s bandwidth. Therefore this memory module is also denoted as PC2100 (DDR266/PC2100).

In some cases, the memory module is in the format PCy yyy as is the case with PC2-6400. This means that this memory module can transfer data at 6,400 MB/s. "PC2" indicates that we are dealing with a DDR2 memory chip (DDR2 800/PC2 6400)

Before Upgrading Notebook Memory...

* Compatibility is the most important concern you'll have when you want to upgrade notebook memory. You'll have to ensure that your notebook can support the type of memory you'll be purchasing.

If your notebook comes with 200-pin DDR SO-DIMM memory slots, don't go out and buy a 200-pin DDR2 SDRAM no matter how tempting it might be.

Because of the different pin set-up, you won't be able to fit a 200-pin DDR2 SDRAM module into a slot meant for a 200-pin DDR SDRAM.

You should check your notebook's manual or the manufacturers website/customer service for information on memory type, capacity and speed.

* Notebook computers typically have two memory slots. Sometimes only one of those slots is available for upgrading memory without pulling apart the entire notebook.

* System RAM can be picky so when you're using two memory sticks, try to ensure that they are the same brand and speed. This will prevent compatibility issues and increase the chances to getting the best performance.

If your notebook supports PC3200 DDR400 RAM but a single PC2700 RAM is installed, you will need both memory sticks to be PC3200 to give you DDR400 speed. If when you doing the upgrade, you install PC2700 and PC3200 memory stick together, the system will decelerate to PC2700 speed.

* Sometimes, RAM is downwardly compatible. For instance a PC2700 (DDR333) RAM can operate in PC2100 (DDR266) mode when the notebook only runs PC2100 RAM.

* DDR2 is neither forwardly nor backwardly compatible with either DDR or DDR3

* Modern computers use dual-channel architectures. This is just a pretty way of saying that information is transmitted through two separate pipes. This leads to greater memory bandwidth.

If you only have one stick of money or use two sticks, each of which have different capacities (e.g. IGB and 2GB), then your dual channel system will run in the lesser-performing, single-channel memory mode.

* Most notebooks have a RAM size limit which means that they have a maximum amount of RAM they can support. So even if your notebook can physically accommodate 2x1GB memory modules, it only make use of 1GB of RAM if the RAM limit is 1GB

* Want to easily identify exactly what kind of memory your system uses? You download a free version of AIDA64; it will indicate the type of memory your system uses.

Coming Up...

In part 4 of this notebook memory guide, we show you how to install notebook memory. Check it out.

If you have not already done so, read part 2 of this guide which tells you how much laptop memory you need.

Or read part 1 which tells you to how prevent low laptop memory problems.

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Leave Notebook Memory & Return To Laptop Memory Part 2

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