DDR3 240-pin DIMM

In newer systems using SDRAM or DDR SDRAM memory, you can use modules of different densities with no problem. For example, if your computer came with a 128MB memory module, you can add a 256MB module for a total of 384MB of RAM. However, if you have a "dual-channel" system and want to take advantage of that technology, you will need to ensure that the modules in each memory slot are the same density.

Memory is designed to be backward-compatible, so generally speaking, you can safely add faster memory to a computer that was designed to run slower memory. However, your system will operate at the speed of the slowest module or system component (the "lowest common denominator" effect).

One thing to keep in mind is that the memory does need to be the same type — for example, SDRAM cannot be mixed with DDR, and DDR cannot be mixed with DDR2. We recommend that you use the Crucial Memory Advisor™ or System Scanner tools to find the right memory for your computer.

That depends on two factors: the amount of memory your computer hardware can handle, and the amount of memory your Microsoft® Windows® operating system (OS) can handle.

First, your computer hardware (motherboard) is designed to hold a maximum amount of RAM. When you look up your computer in the Crucial Memory Advisor™ tool or scan your system with the Crucial System Scanner, you will see the system maximum listed on the page that shows the compatible upgrades for your system.

Second, the OS maximum is the maximum amount of memory that your particular version of Windows, Linux, or Mac® OS can handle.

When purchasing your memory upgrade, make sure that you do not exceed the lower of the two maximums (OS and computer maximums.) Too much RAM can lower your system's performance or cause other problems. (In most cases, the system maximum is lower than the OS maximum.)

Windows 7 (32 Bit)

Starter: 2GB

All other Versions: 4GB

Windows 7 (64 Bit)

Home Basic: 8GB

Home Premium: 16GB

Professional: 192GB

Enterprise: 192GB

Ultimate: 192GB

Windows Vista (32 bit)

Ultimate: 4 GB

Enterprise: 4 GB

Business: 4 GB

Home Premium: 4 GB

Home Basic: 4 GB

Starter: 1 GB

Windows XP (32 bit)

Professional: 4 GB

Home: 4 GB

Starter Edition: 512 MB

Windows Server 2003 (32 bit)

Datacenter SP2: 128 GB

Enterprise SP2: 64 GB

Standard SP1: 4 GB*

Datacenter R2: 128 GB

Enterprise R2: 64 GB

Standard R2: 4 GB*v
Web Edition: 4 GB*

Small Business Edition: 4 GB*

* Certain Microsoft server operating systems can support over 4GB of memory via Physical Address Extension (PAE). Please refer to Microsoft knowledgebase article located here for more information.

Windows Server 2008 (32 bit)

Datacenter: 64 GB

Enterprise: 64 GB

Standard: 4 GB

Web Server: 4 GB

Windows Vista (64 bit)

Ultimate: 128 GB

Enterprise: 128 GB

Business: 128 GB

Home Premium: 16 GB

Home Basic: 8 GB

Windows XP (64 bit)

Professional: 128 GB

Windows Server 2003 (64 bit)

Datacenter SP2: 2 TB

Enterprise SP2: 2 TB

Standard SP1: 32 GB

Datacenter R2: 1 TB

Enterprise R2: 1 TB

Standard R2: 32 GB

Small Business Edition: 128 GB

Windows Server 2008 (64 bit)

Datacenter: 2 TB

Enterprise: 2 TB

Standard: 32 GB

Web Server: 32 GB

Here are the OS maximums for some older versions of Microsoft Windows:

• Windows 95: 1GB


• Windows 98: 1GB


• Windows 98SE: 1GB


• Windows ME: 1.5GB


• Windows NT: 4GB


• Windows 2000 Professional: 4GB


• Windows 2000 Server: 4GB


• Windows 2000 Advanced Server: 8GB with PAE enabled


• Windows 2000 Datacenter Server: 32GB with PAE enabled

Here are the maximums for some other platforms:

• OS X (including v. 10.4 "Tiger"): 8GB due to current hardware limitations (the current maximum memory capacity of Apple's highest-end system, the Power Mac G5)


• OS 9.x: 1.5GB (no single application can utilize more than 1GB)


• Red Hat Linux 2.4 kernel: 64GB

Once you have found your computer in the Crucial Memory Advisor™ tool, locate the maximum memory capacity and number of memory slots for your particular computer. Generally speaking, you can determine the largest memory module each slot can take by dividing the maximum capacity by the total number of slots. For example, if your computer has a maximum memory capacity of 2048MB (i.e. 2GB), and has two slots, the largest module you can install in each slot is a 1GB memory module.

However, there are exceptions to this general rule. For example, there are situations where a computer with 4 memory slots and a 2GB maximum memory capacity will accept two 1GB modules. There are also times when a system would only accept a 512MB module at launch, but down the road would take a 1GB module with a BIOS upgrade. This is why it is so important to use the Crucial Memory Advisor™ tool which can alert you to these exceptions.

To completely "max out" the memory on your computer, you may need to actually remove memory modules currently installed and replace them with larger-capacity modules. Using the example above, if your computer has one 512MB module already installed, with one memory slot open, you would need to remove the 512MB and install two 1GB modules to truly "max out" your computer.

Most desktops and notebooks use one of four popular types of dynamic random access memory (DRAM) for the main system memory.

Single data rate (SDR) SDRAM is the older type of memory, commonly used in computers prior to 2002.

Double data rate (DDR) SDRAM hit the mainstream computer market around 2002 and is a straightforward evolution from SDR SDRAM. The most significant difference between DDR and SDR is that DDR reads data on both the rising and falling edges of the clock signal, enabling a DDR memory module to transfer data twice as fast as an SDR memory module.

Systems implementing the follow-on technology to DDR, called DDR2 began to appear in mid-2004. DDR2 achieves speeds beyond that of DDR, delivering bandwidth of up to 8.5 GB per second. Frequently, DDR2 based systems can use memory installed in pairs to run in "dual channel mode" to increase memory throughput even further.

The latest generation of memory technology, DDR3, began to appear in systems in late 2007. DDR3 is an evolutionary step beyond DDR2 and operates at lower voltages, thereby consuming less power, and can transfer data at rates up to 12.8 GB per second. Typically, DDR3 based systems can address memory modules in banks of 1, 2 or 3. If a system supports it, installing memory in matched sets of 2 or 3 modules (dual channel or triple channel modes) will deliver greatly increased memory performance over running a single memory module by itself.

Generally speaking, motherboards are built to support only one type of memory. You cannot mix and match SDRAM, DDR, DDR2, or DDR3 memory on the same motherboard in any system. They will not function and will not even fit in the same sockets.

The right type of memory to use is the one that your computer takes! The easiest way to find the right memory for your computer is to look up your system in Crucial's Memory Advisor tool. The Memory Advisor tool will list only compatible memory for your system.

If you don't know the exact model of your computer, the Crucial System Scanner can scan your computer hardware to automatically detect your system configuration and give you a report on which upgrade is right for you.