2 x 1GB Dual Channel or 2 x 2GB

[miecz]

I have a Macbook Pro. I do not know which way to go: 2 x 1GB Dual Channel or 2 x 2GB. Can anyone please help me? I think I heard that it does not really matter because both equal 4GB of total RAM. Is that true?

 

[miecz]

No one knows?

 

[sailer]

Both would not equal 4 gig of ram. That's simple math. Generally speaking, the 2x2 gig sets don't have as fast timings as a 2x1 set, but there's also advantages to running 2x2 set, like if you eventually want to go to 8 gig total in the future. You need to check the manual to find out what ram sets are supported, along with the operating system and what it supports. For example, the motherboard might not support a 2x2 gig set, or the operating system might not support it. Can't help you on those questions without knowing the particulars of your machine.

 

[miecz]

Thanks for the reponse. The limit on RAM on the machine is 4GB max. There are 2 slots.

I have another question. I thought that 1 stick of dual-channel RAM runs as fast as 1 stick of 2GB. Is this incorrect?

 

[sailer]

That's incorrect. You're mixing ideas. Dual Channel refers to the data path, wherein a single channel runs at 64 bit and dual channel runs at 128 bit. Dual channel does not have anything in particular to do whether the ram stick is sized as 512, 1 gig, or 2 gig. Ram sticks, however, may be restricted to single channel in their manufactor. This was true of all ram types built years ago. Most ram sticks are made to work in dual channel mode now. While theoretically a single stick of ram can run in dual channel mode, the usually setup is to use two sticks of identical ram.

 

[miecz]

So, if I have 2 x 1GB dual-channel RAM, it is not running as 4GB total? Is that correct?

 

[sailer]

If you have a 2x1 dual channel ram, you only have 2 gig of ram. By being dual channel, it is running a 128 bit data path, instead of a 64 bit data path used with single channel ram. You can look up a detailed explanation on Wikipedia.

 

[miecz]

Is the difference in speed great between dual-channel and regular channel?

 

[sailer]

Yes, dual channel doubles the bandwidth of single channel. Don't worry about it too much. Vitually all ram made is dual channel now, unless you're buying PC2100 ram or something, and no modern computer uses that.

 

[miecz]

Sorry to beat this dead horse, but let us say you have 2 x 1GB and 2 x 1GB dual-channel, what percent of a difference will there be in performance between the 2? And thanks for all of your responses.

 

[sailer]

Yes, you are beating a dead horse. But simply put, a 2x1 gig dual channel will have twice the size of a data channel as 2x1 gig single channel, thus transfering data at twice the speed and that will give a like increase in performance.

 

[miecz]

Oh, you are going to hate me now. lol. I have another question, the one I had at the beginning but a little different. By your last response, it would seem that 2 x 1GB dual-channel RAM has the same speed as 2 x 2GB single channel RAM, correct? Sorry again if it is annoying. i do not want to make a bad move in buying the wrong RAM.

 

[sailer]

First of all, I don't think anybody makes 2x2 gig sticks of ram that are single channel. And you have data transfer mixed up with speed and capacity. Try thinking of it this way. By doubling the data channel path, twice as much information can be moved at a time as with single channel. An example would be it you picked up and moved 128 things (dual channel) as opposed to picking up and moving 64 things (single channel). One trip in dual channel moves twice as much information at a time. This is a crude explaination, but should suit the purpose. The dual channel does not determine the speed, but the quantity of information moved at a time, although if both sets of ram were running at the same timings, the dual channel would move information twice as fast.

Speed refers to how fast the data is being moved. A stick of ram has speed timings, usually expressed in a series of numbers like 4-4-5-10, or something similar. The first number exresses the speed that the data is moved, with a smaller number indicating a higher speed. Thus ram rated at 4-4-5-10 would move the data at roughly twice the speed as ram rated at 8-8-10-12 (example only, not exact timings of any particular ram). Bandwidth also enters the equation, but I'll skip that for now. Thus a 2x1 gig set with a timing of 4-4-5-10 would have the same speed as a 2x2 set of ram that operated with a timing of 4-4-5-10.

Using a 2x1 gig set of ram means that the ram can store 2 gig of memory. A 2x2 gig set would store 4 gig of memory. That has nothing to do with speed, but with storage capacity.

I have to go to work now. What you should do is spend some time reading through Wikipedia for detailed answers, or get a book at a library and read it. Other than that, read through the manual that came with your compter or go to Apple and get their recommendations of the specific ram you should use with your computer and operating system. I can't tell you anything specific as to what ram to buy, only give you general guidelines. By now.

 

[jwolf24601]

2x1gb or 2x2gb or 2x4gb are all about the same speed.

What varies is the amount of memory.

Say you've got two stacks of apples, 1 stack of apples has 50 apples the other has 100 apples, you still eat the apples at the same rate but in one you run out sooner. That's what the GB refers to.

The speed on the chips is PC5300 PC6400 number.

If you buy 2 of the same type of memory it should always run dual channel if the computer is less than 5 years old.

Read your motherboard's manual and make sure you get compatible memory. Or take it to a bestbuy and have them put it in for you (no offence you just dont seem like you're comfortable with the specifics)

 

[miecz]

Thanks guys. I called a computer store and the guy told me that there is the same performance on 2 x 1GB dual-channel and 2 x 2GB single channel.

 

[ddrum2000]

The guy at the computer store is more/less correct. Since you are using a Macbook Pro, you are probably using DDR2-667 modules. Further more you don't have a traditional PC BIOS to change the timings so you won't benefit for the low latency RAM that others are speaking of. I believe the standard timings on DDR2 RAM is 5-5-5-15 so if you get 2x1 GB or 2x2 GB with same timings the speed will be just about the same. Also I don't know what kind of work you are doing but 4GB of RAM may be overkill.

For a 2GB kit I would get:
http://www.newegg.com/Product/Product.aspx?Item=N82E16820145157

For a 4GB kit I would get:
http://www.newegg.com/Product/Product.aspx?Item=N82E16820144066

Bottom line is check the review to make sure its Mac compatible (they are a bit more picky with RAM then other computers). You do not need to buy "Mac memory". As I am sure you know Macs are now just PCs with with a different OS installed. I hope I answered you questions.

 

[miecz]

Why would you recommend the 4GB kit if it is has the same performance of the 2GB kit that is like 1/3 the price?

 

[Hatman]

I use 4gb 4x 1gb single channel Stupid value ram lol..

2x 1gb dual channel vs 2x2gb single channel.. you cant really compare them.

4gb of ram can hold more information, so using something like vista64 may get a desent performance boost. But it will be slower processing the data and using it.

But as said, all 2x2gb modules DO run in dual channel, so your question is kinda wrong. It should be:

"Can I afford to buy 2x2gb dual channel over 2x1gb dual channel?"

If ya can afford it, go ahead, there will probably be some performance boost.

 

[pavel-]

more capacity (4gb) means the OS does not have to go to the hard disk (VERY VERY slow) as often to use swapspace, so if you are running a lot of applications on a robust OS at the same time, 4gb is the way to go, but 2gb usually suffices for almost all general and sometimes even professional use.

unfortunately the speeds of hardware in computers are unsynchronized,
the CPU is MUCH faster than RAM, which is in turn is MUCH faster than the hard disk.