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What is DDR RAM?

By R. Kayne
Updated May 16, 2024
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Double-Data-Rate Synchronous Dynamic Random Access Memory, better known as DDR SDRAM or DDR RAM for short, is a type of very fast computer memory. It's based on the same architecture as SDRAM, but uses the clock signal differently to transfer twice the data in the same amount of time.

In a computer system, the clock signal is an oscillating frequency used to coordinate interaction between digital circuits. Simply put, it synchronizes communication. Digital circuits designed to operate on the clock signal may respond at the rising or falling edge of the signal. SDRAM memory chips used only the rising edge of the signal to transfer data, while DDR RAM transfers data on both the rising and falling edges of the clock signal, making it essentially twice as fast as SDRAM.

RAM speed works in conjunction with the front side bus (FSB) of a computer system. The FSB is the two-way data channel that sends information from the central processing unit (CPU) throughout the motherboard to the various components, including the RAM, BIOS chips, hard drives and PCI slots. Therefore, a computer system with a FSB of 133MHz running DDR SDRAM will essentially perform like a 266MHz machine.

The 184-pin DDR RAM dual in-line memory modules (DIMMS) only work properly in a motherboard designed for their use. While this RAM comes in various speeds, installing a version faster than a motherboard can support is a waste of money, since it will only run as fast as the motherboard permits. It is visually differentiated from SDRAM in that SDRAM is a 168-pin DIMM with a double notch at the bottom along the pins — one notch just off-center, the other offside. The 184-pin DDR SDRAM has a single off-center notch.

DDR RAM is generally made for processors 1GHz and faster. Designations like PC1600 DDR SDRAM and PC2100 DDR SDRAM coincide with particular FSB and CPU speeds. RAM manufacturers use different schemes to designate processor speed, and the various technicalities in RAM designations and standards can be confusing. Computer users should check their motherboard manual to see what RAM type is compatible with their system before purchasing memory.

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Discussion Comments
By anon241280 — On Jan 18, 2012

How to check my RAM without opening the case:

Download cpu-z; install it; go to tab SPD.

I just read on google about what the difference is between ddr and ddr3. --chrissie

By anon238542 — On Jan 04, 2012

DDR rams are very useful tools that are used all around the world for personal and also mainframe computers.

By amypollick — On Nov 19, 2011

@shellyann: Since the LED light isn't glowing, I'd check the power cord. Make sure it is plugged securely into the back of the tower, as well as into the wall outlet or power strip. Make sure your power strip is turned on and is rated for the number of plugs it is using.

I don't think this has anything to do with the memory. I'd start looking at the power supply. You might try plugging it into another outlet, just to make sure the wall outlet you were using isn't the problem.

If none of this solves the problem, I'd take it to a computer repair shop. Good luck.

By shellyann — On Nov 19, 2011

I tried to turn on my desktop computer, but it would not start (note: LED/status light on the system unit isn't lit/glowing). My system has the following specifications: Motherboard: micro ATX G965. RAM: DDR2.

Processor: Intel Core 2 duo Processor. Operating system: Windows XP

What are some possible issues associated with this problem and how would you troubleshoot?

By anon166069 — On Apr 07, 2011

"Therefore, a computer system with a FSB of 133MHz running DDR SDRAM will essentially perform like a 266MHz machine."

How can a system run at 266Mhz if FSB is only 233Mhz? To me it seems that memory will perform twice as fast, but FSB stays the same.

By jaichand — On Jan 06, 2011

My PC has 1 GB DDR RAM. is it possible to upgrade it to 4 GB DDR RAM?

By anon138366 — On Dec 31, 2010

why am i having trouble downloading an ecard? For that matter i can't go to any music web site without an error message.

By anon109484 — On Sep 07, 2010

Whats the price of DDR1 and DDR2? which brand is good?

By anon64984 — On Feb 10, 2010

Some sites will scan your pc and tell you what upgrades you can buy. if you're choosing to buy somewhere else, make sure upi take notes on what it says. What DDR is it? What speed and max upgrade?

If it says your machine only supports 2gig don't buy 4. seems obvious but...

also if running a 32 bit version then windows only recognises max 3.5 gig of ram. get aq 64 bit version if you want max.

By anon62577 — On Jan 27, 2010

which is better ddr or ddr-3

By anon59875 — On Jan 10, 2010

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.

By anon55336 — On Dec 07, 2009

hey i want to make my own computer. Can anyone help me to get the information for the best performance and brands of computer parts?

i'm a net surfer and game player.

By ramsupplier — On Dec 01, 2009

hello sir. I'm just wondering why my ddr ram 512 in ddr slot 1 don't work in ddr slot 2

Thanks to everyone.

answer: check with your motherboard.

By ramsupplier — On Dec 01, 2009

Q1) How do I check if my computer has DDR or DDR2 without opening my computer's case? i mean from the windows - is there any way ? cause i lost my computer's manual :S

A1)Maybe you can try to check the control board of computer and then you will see all specifications of your computer.

By ramsupplier — On Dec 01, 2009

To Anon783: Re: The difference between DDR2 and DDR1. DDR2 is updated products based on DDR1, and DDR2 is faster and saves more power. the thermal diffusivity of DDR2 is better than DDR1 because they use different package technology during production.

By anon51592 — On Nov 07, 2009

Q1) How do I check if my computer has DDR or DDR2 without opening my computer's case? i mean from the windows - is there any way ? cause i lost my computer's manual :S

By anon50653 — On Oct 30, 2009

Very nicely explained the topic in all respects.

By anon41185 — On Aug 13, 2009

The difference between DDR and DDR2 is the amount of data in bytes that will be transferred per clock cycle of the CPU. Think of the clock cycle as a wave length. DDR sends 1 byte of data per pin which is normally 8 per rise of clock cycle and fall of clock cycle so 16 bytes per clock cycle. DDR2 doubles that and sends 2 bytes of data per pin per rise and fall of clock cycle.

By anon36748 — On Jul 14, 2009

Q1) How do I check if my computer has DDR or DDR2 without opening my computers case, i mean from the windows - is there any way ? cause i lost my computers Manual :S

A1) Go to "Run" and type 'dxdiag' it shows your computers specs.

By reijii — On Jul 14, 2009

hello sir. im just wondering why my ddr ram 512 in ddr slot 1 don't work in ddr slot 2

Thanks to everyone.

By anon34689 — On Jun 26, 2009

Very well explained and presented. The Author of this article has thought about to put the information in a simple way yet covering the whole topic.

I would rate this an A+.

By santhoshhv — On May 08, 2009

Will our computer have trouble if we use a tv tuner card(external) with it?

By anon26445 — On Feb 13, 2009


I need a computer which is fast for calculations and has good graphics and that can be used with both windows and linux. What kind of computer do I need for optimum performance?

By anon25073 — On Jan 23, 2009

i want to buy a laptop....will there be any prob if i config...as customerisation option is provided by dell....

some are say is that its better buy specific model than configuring a laptop....pls help me....thanks

By HACKadelick — On Jan 02, 2009


My Toshiba has a Penti4,3.06GHz process,80GB HDD,512MB of DDR SDRAM.

Can someone tell me why the new Logitech web cam keeps freezing my computer?

By anon11079 — On Apr 08, 2008

dude its not that difficult to check whether your ram is DDR or DDR2. sad news that there is no way to find out without opening your cabinet through windows. just open your cabinet screws and flip UP the ram socket's edge triggers. RAM automatically pops out doing so. it is always written on the ram itself about its configuration. Then with a little caution of placing notch of RAM on the slot (see thoroughly the slot for the place for notch). and fix RAM urself as you popped out. trust me its not that techie to do this

have nice computing

By anon10802 — On Apr 03, 2008

CPU-z will give a lot of information about your computers hardware including memory.

By anon4594 — On Oct 24, 2007

I've been using 512 mb for years - And i m a professional gamer, I havnt faced in Ram problem till now, and in fact i play heavy games like WoW and battle of middle earth with msn On and real player Songs on... So to conclude 512 is more than enough for me..|

Q1) How do I check if my computer has DDR or DDR2 without opening my computers case, i mean from the windows - is there any way ? cause i lost my computers Manual :S

it would be a great favor if you guys reply

By anon4248 — On Oct 09, 2007

At present my computer has a 128mb ddr ram...can it be replaced by a 1 gb ddr1/ddr2...or does it have to be 1gb ddr?

By issa9999 — On Sep 16, 2007

hi, 2gb enough ram to run all games out today and you would struggle to see the benefits of another 2gb of ram.

By anon3749 — On Sep 15, 2007

I'm going to build a computer. How much RAM do you need? 2GB seems to be required but will 4GB make any big difference?

By issa9999 — On Jul 10, 2007

hi, well it depends on what you use your computer for, 512gb of ram is enough for quite a lot of games and browsing the internet but if you want to play more graphically demanding games i recommend getting another 512 stick of ram, you don't need 2gb, 1gb will do.

By anon2400 — On Jul 10, 2007

i am a new computer user i don't know how the ddr ram works. is it necessary to have a 2 gb ram? i have 512 mb ddr ram & 80 gb hard drive

By issa9999 — On Jul 02, 2007

hi, my motherboard is running at 140 fsb and my cpu multiplyer is 20 which makes my cpu run at 2.8ghz which im fine with however i have 2 sticks of 512mb pc3200 ram which should run at 400mhz however if my fsb is 140 my ram must only be running at 280mhz, how do i make my ram run at its correct speed as i cannot raise the motherboard fsb anymore as it becomes unstable as it overclocks my cpu to high. also cpu-z tells me that my ram is at 200 mhz so if that is doubled its 400mhz which is what i want but how is it possible if my motherboards fsb is 140 surly my fsb would need to be 200 in order to run my ram at 400mhz.

By anon783 — On May 04, 2007

what is the difference between ddr2 & ddr1?

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