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Why do I need to upgrade RAM?

  • I want to upgrade my OS to Windows XP (RAM: 256MB recommended)
  • I feel too slow if I load too many programs at the same time
  • My harddisk's LED keeps flashing - a symtom that the PC is running out of memory(RAM) and started using the harddisk intensively for caching purpose by means of virtual memory

Memory - RAM - Random Access Memory. RAM is by far the easiest and most productive of upgrades to do. RAM is your computer's short-term memory, which it uses to store the information that you are working on. Adding memory will allow your applications to open faster. There are a great number of different types of memory (EDO, PC66, PC100, PC133, DDR2300, DDR3300 etc.).

The SDRAM DIMM is the most widely used memory type in older standard desktop systems. SDRAM has various speeds; 66Mhz (PC66), 100Mhz (PC100) and 133 Mhz (PC133).

SDRAM was a huge improvement on previous types of RAM because it eliminated a lot of wait time. Traditionally the system bus (which is all the circuitry on the motherboard that moves data around a computer) and RAM had to wait for each other to do their part in processing information. SDRAM changed that. Now the bus and the RAM work at the same time. There's no tag team silliness going on.

NOTE: DIMM stands for dual inline memory module, SDRAM stands for Synchronous Dynamic RAM

SDRAM is a kind of memory chip that was introduced around the time that Pentium II computers appeared. If you have one of those computers today, chances are that you are in the market to add memory to extend the life of the computer.

Only buy the correct speed for your motherboard. You need to check the motherboard's specification before making the purchase. If the specs says that the motherboard only supports 100 MHz SDRAM, then buy only PC100 SDRAM only.

66MHz modules will not work on a 100/133MHz bus speed.

While some 133Mhz module will work on 100Mhz motherboard, do not assume all 133Mhz memory work on 100Mhz motherboard.

What if PC100 RAM is not available in the market? Can I mix the PC133 with my existing PC100 RAM?

If your motherboard is able to support PC133 and you already have an existing PC100, you can mix the PC133 with PC100. The PC will configure itself to run at the speed of the slowest RAM installed. So if you can afford to dump your PC100 RAM and replace it with PC 133 you can take advantage of the faster technology. I won't advise you to do so, as PC133 is only slightly faster than PC100 RAM.

Single Sided (x4) - Newer standard

In addition, please check with motherboard manufacture to see if the motherboard bios support 256MB(32x4) or 512MB(64x4) new standard. If not, it will only read half of the memory capacity even though your computer starts up normally.

Please contact your motherboard manufacture to update the bios to accept (32x4) or (64x4) new standard.

Generally, for motherboard that accept (32x4) or (64x4), it must be able to take 512 MB in each memory slot, If the motherboard doesn't support (32x4) or (64x4) standard, please order the (16x8) or (32x8) standard.

Double Sided (x8) - Older standard

If you are upgrading an old mb (say P3), choose PC133 256 mb double sided SDRAM. It fits all older motherboards that do not support single sided SDRAM.


You may also have heard of DDR SDRAM. This is an even faster kind of memory called double data rate memory. DDR memory moves data at 266MHz, but don't call it PC266 SDRAM.

To use DDR memory, your system has to specifically support the technology. Typically PCs that run Pentium III or Pentium 4 processors that run at 1 GHz or faster will support DDR RAM, but don't assume that all will. AMD Althon processor-based machines also tend to support DDR SDRAM. Check with your computer maker to ensure that the motherboard supports DDR RAM. Or look up your system on Crucial.com to find out.

When buying DDR SDRAM you'll be faced with few choices. They are PC1600, PC2100, PC2700, PC3200(DDR400) ...

While your motherboard may support DDR memory, you will need to check to see that it supports PC2100 DDR SDRAM. Some early models of DDR-enabled motherboards only work with PC1600. You also need to ensure that the processor for your computer can support PC2100.

PC1600 DDR is designed for motherboards and processors with a 200 MHz bus and PC2100 DDR is designed for a motherboards and processors with a 266 MHz bus. Remember that the bus is all those circuits on the motherboard that moves data around. They are kind of like data highways that run between the processor and RAM and all the other components in a computer.

Once again, a computer with a mix of PC2100 and PC1600 DDR SDRAM will default to the slower RAM speed.

If you need more info, check out Crucial.com's amazing RAM guide. Go to Crucial.com and click the "Library" tab for lots more useful RAM information.

It's easy to figure out what RAM your system needs. You just select your brand and make and model of the system and then Crucial shows you which RAM will work with your computer.


Pin Configuration

DDR2 240-pin DIMM

DDR 184-pin DIMM

PC133 168-pin DIMM

PC100 168-pin DIMM



Most desktop computer use non-ECC (error correction), non-registered, and non-buffered memory modules.

ECC and registered memory modules are normally used by servers that require these features and ECC memory are far more expensive than the non-ECC memory.

CL stands for CAS Latency.

When a module is labeled CL2 it means there are only two clock cycles before the module can send the first block of data.

CL3 means there are three cycles before the first block of data is sent.

Cl2 is considered to be a small percentage faster than CL3 modules.

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Last Update: 17 October 2002