Memory (RAM) Buying Guide

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Memory (RAM) Buying Guide

For a computer to execute more tasks, a very efficient system memory or RAM is needed. As a rule of thumb, more RAM is better than less RAM. RAM, which is the chips inside a PC where information is stored, is often called simply as "memory". There are different types of RAM that can be bought online, from the basic type to the industry standard that allows computer users a more convenient computer experience, but, of course, for a higher price. Aside from the different types, buyers may also need to consider the different brands which offer all types of RAM.

The stream of information regarding memory can be quite confusing for a first time buyer of PCs or those who like a memory upgrade. To add to the challenge, buyers who are on the lookout for the better or best RAM must know the variety of form factors which determine the shape and size of a memory. When it comes to purchasing RAM, buyers must be equipped with the right product knowledge to arrive at a wise choice. Whether consumers wish to purchase RAM within a local high street technology shop or online with websites like eBay, a bit of knowledge is invaluable.

Evolution of RAM

System memory or RAM has undergone several upgrades since the 1990s. During that year, computers were becoming more advanced, but along with the benefits of the changes, there were also problems that arose.


Computer users were having a problem with the DRAM, the then industry-standard type of RAM. The DRAM could not keep up with all the commands from the processor because it operated separately from the processor, with the DRAM using as an asynchronous interface. Because of the inefficiency of the DRAM, a new breed of RAM was developed: the SDRAM. This type of RAM eased up the process by aligning the memory's responses to control inputs with the system bus to line up one processor request while waiting for another. The queuing allows the computer to speed up the coming and going of requests, making it do more. By the end of the 90s SDRAM replaced DRAM as the most reliable RAM in computer systems.

The original SDRAM, no matter how better it was at that time compared to the DRAM, still fell short when it comes to efficiency. Regular users and hardware developers alike began to notice the limitations of the SDRAM and its operation through a single data rate (SDR). The original SDRAM could still process one command every clock cycle, and since computers were becoming mainstream during that time, more complex commands to the processor were becoming a regular occurrence, rendering SDRAM obsolete.


The solution came in a three-letter acronym: DDR. The Double Data Rate or DDR processed information once at the rising edge of a clock signal and another at the falling edge, twice as fast as the regular SDRAM. The speed at which the DDR process information yielded other benefits, including using less energy, operating up to 400 MTps and running from 100 to 200 MHz. Times changed, and so must the memory.

To keep up with the rapid advance in computer technology, DDR2 was introduced. DDR2 could complete a movement of information at half the speed of the data bus, making it twice faster than the DDR. It has a transfer rate of up to 1,066 MTps, and it even consumes lesser energy, using 1.8 volts compared to the 2.5 volts used by DDR. With computers demanding more efficiency in RAMs, the DDR3 was released in 2007. DDR3 cut the duration of information movement in half again, reducing energy consumption to 1.5 volts, and provided a maximum transfer rate of 2,133 MTps. DDR4 is the next step in the evolution of RAMs, but it is not available as of this moment. Computer users are expecting its release in 2014.

Summary of Different Types of DDR RAM

The table below shows the different types of DDRs as well as their key characteristics. The DDRs are compared based on information processing speed, energy consumption and transfer rate.

Type of RAM

Information Processing Speed

Energy Consumption

Transfer Rate


Twice as fast as the regular SDRAM

2.5 volts

Up to 400 MTps


Twice as fast as DDR2

1.8 volts

Up to 1,066 MTps


Twice as fast as DDR3

1.5 volts

Up to 2,133 MTps

The information above can be a quick guide reference for buyers opting for DDRs. Needless to say the DDR3 is the most superior type of DDR RAM.

RAM Form Factors: Considering Sizes and Shapes

Aside from knowing the types of RAM, buyers must also be aware of the fact that RAMs come in different shapes and sizes. This part of the buying decision is easy because each of the different form factors corresponds to a certain age of computing.

30-Pin Single Inline Memory Module (SIMM)

The 30-Pin Single Inline Memory Module is the standard for the 286/386 field, with the 30-pin SIMM about one half the width of another SIMM form despite having an eight-bit pathway. Computers that have higher density form factors require these forms that have wide data paths.

72-Pin Single Inline Memory Module (SIMM)

Another form factor is the 72-pin Single Inline Memory Module. It is a common type and an industry standard for many Pentium motherboards and many 486 or Pentium Pro boards. This SIMM has 32-bit wide paths.

Dual Inline Memory Module (DIMM)

The Dual Inline Memory Module , with its capacity to accommodate a 64-bit memory path, is the most common form factor for RAMs today. Such form factor is equipped with a split section pin array having a third notch on the left side to accommodate the 168 pins.

Rambus Inline Memory Module (RIMM)

The Rambus Inline Memory Module is basically like a DIMM in terms of being a form factor aside from the RIMM having a very different pin configuration. It was first made to hold the direct RDRAM chips.

72-Pin Small Outline Dual Inline Memory Module (SODIMM)

Typically used in the Pentium II laptops, the 72-pin SODIMM module has a memory capacity from 8.16 to 32 megabyte and a 64-bit configuration. During a low-power application only one voltage is offered. The typical DRAM type available for a 72-pin SODIMM is the EDO and fast page mode.

144-Pin Small Outline Dual Inline Memory Module (SODIMM)

The 144-pin small outline dual inline memory module is often used in PC100 and PC66 laptop compatible computers. It is available in 64-bit and 72-bit memory ECC configuration and capacity range and memory capacity range up to 256 megabyte.

Buying RAM on eBay

eBay lists a wide variety or memory or RAM types. Whether you are looking for a SDRAM, DDR, DDR2, or DDR3 you can easily find one on eBay. Whatever your brand preference, HP, Adata, or IBM, the site has tens of thousands models to choose from.

When searching for a memory or RAM on eBay, simply type the keywords such as " DDR2 RAM " or " Memory SODIMM " into the search bar and you will be presented with a wide number of options. What is great about eBay is, with just a bit of navigating around the site, you can learn to filter your search based on a number of preference options that the site provides. Sellers on eBay are either individuals or companies with their own online shops on the site. It is always recommended to buy from a top-rated seller because they already have a reputation for providing excellent customer satisfaction. eBay can also be your one-stop shop for all your computer and tablet parts needs.


A computer cannot execute tasks without the help of a RAM. There are different types of RAM, and each is created to respond to the requirements of computers as they get more complex and complicated over time. The DRAM was the ideal RAM type before it was replaced by the more efficient SDRAM in the 1990s. However, computer technology continues to advance, and with each milestone a new type of RAM needs to be created to meet the information processing speed and transfer rate demands of computer users.

DDR was the first to replace SDRAM as the industry-standard RAM, with DDR moving information twice the speed of the regular SDRAM. It also lowered the energy consumption to 2.5 volts and increased the transfer rate up to 400 MTps. DDR was replaced by DDR2 and DDR3 subsequently, with each type being twice as fast as its predecessor, having lower energy consumption, and higher transfer rate. On the other hand, the form factor is also an important consideration when buying a RAM. DIMM and SO DIMM form factors are the most common types of form factors today. A system memory or RAM will definitely continue to evolve, and it is important to know its functions and specifications when purchasing so buyers can make a wise decision in their current purchase and can prepare for a future upgrade.

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