Understanding R.A.M

In this article I will attempt to explain memory, R.A.M., its different flavours and what it means to the End User. At times I will go into far more technical detail than some of you want to hear, and at other times I will leave some of you wishing that I had said more, I'm sorry to both of you, my intention is not to provide a "R.A.M. for dummies" nor a technical reference, just a guide.
Maybe I'll clear-up some misinformation you've previously learned along the way.
Maybe someone will spot a mistake, please point it out to me.

Question: What Is R.A.M.?
Answer: R.A.M. stands for Random Access Memory. Why is it called Random Access Memory? "random" because the computer can read or write at any given time... as opposed to R.O.M. or Read Only Memory.
R.A.M. only holds data while the Computer is running, when you turn the computer off anything held in R.A.M. is lost, (one good reason to shut-down correctly, so that your computer has the opportunity to save data to the more permanent but slower Hard Disc), a good analogy for R.A.M. is your physical desktop, I mean the piece of wood your elbow is resting on as you read this and your eyes glaze over...

It holds the data you are using at the moment, files you have open and programs you have running, like Outlook, Word, Internet Explorer and anything else, even the operating system ie: Microsoft Windows / MacOS / Linux.

The more R.A.M. you have the more your computer can handle at any given time. Going back to our desk analogy if you have a bigger desk you can spread out more pieces of paper, a couple of bills, a nasty letter to the Council and if your R.A.M./desk is large enough, you can also have a look at a 6 page credit card statement without having to put anything away in the drawer (which is my analogy for your Hard Disc Drive).

So if you are the type to have many documents and programs open and running simultaneously more R.A.M. is going to make your computer run smoother and faster. If you only ever do one thing at a time and close each program / document before opening a new one, buying more R.A.M. is a waste of money.

So, if you are still awake, you have a rough idea of why lots of R.A.M. is good, for some people, and whether you are one of them.

Most people should stop reading here...

As well as the amount of R.A.M. another important consideration is its bandwidth or speed.

I don't think it's necessary to go too far back in time, the purpose of this document is not as a history lesson, but to help you make an informed decision when buying a new computer or getting an upgrade.


Question: What is SDRAM?
Answer: Synchronous Dynamic Random Access Memory is a type of R.A.M. which is running in time with the CPU front-side-bus (FSB) in the past, the FSB and CPU clock were the same, this is not the case anymore but the R.A.M. is still synchronous with the F.S.B. even if multipliers are applied.

SDRAM has come to mean the older type which the CPU only 'talks to' once per clock cycle (Single Data Rate).

SDRAM operates at 66, 100, 133 or (rarely) 150MHz
And has a 64bit (8Byte) wide data path. (You can think of this as freeway lanes, more lanes means more cars can travel at the same time)

The most outstanding feature of this type of R.A.M. in it's time was that runs at the speed of the FSB (Synchronous). Therefore its designation includes the maximum FSB speed for which it was designed.

Designation:		Bandwidth(speed):
PC66		532MB/s
PC100		800MB/s
PC133		1064MB/s
PC150		1200MB/s

Question: What is DDR-RAM?
Answer: Double Data Rate memory is still synchronised with the FSB but the CPU can 'talk to' it twice each clock cycle

DDR-RAM is the newer type of SDRAM.

The designation for this type of R.A.M. includes the actual bandwidth which makes the designation much more meaningful.

Designation:		Bandwidth(speed):
PC2100		2100MB/s
PC2700		2700MB/s
PC3200		3200MB/s
PC4000		4000MB/s

Since the original writing of this article, DDR2 and DDR3 have emerged, with DDR4 coming soon. The technology is essentially the same, just faster.

Question: What is Dual Channel memory?
Answer: Most commonly associated with DDR SDRAM, originally used in RD-R.A.M. If your computer has been designed to utilise this innovation, its R.A.M. is supplied in two half size pieces, (e.g.: 2x256 instead of 1x512) and the CPU can 'talk' to each of these at the same time, theoretically doubling the bandwidth. Using the table above, if your 512MB of R.A.M. was supplied as 2x 256MB PC3200 in a mainboard designed for dual channel operation its bandwidth would be 6400MB/s


Question: What is RD-RAM?
Answer: RD-RAM runs on it's own memory bus which is a multiple of the FSB, and 'talks to' the bus twice in each clock cycle (like DDR SDRAM), and it utilises two separate pieces of R.A.M. at the same time (see Dual Channel) but the data path was only 16bits (2Bytes) wide therefore if the FSB is 100 MHz the bandwidth is 1600MB/s this would be the case in the very first of the Pentium 4s.
Recently advances in the design have doubled the width of the data path to 32bits and in the near future we should see it double again to 64bits, all of this while still having the fastest memory bus, and even the memory bus is getting faster, from the original 400MHz to the current 800MHz, with 1066MHz just around the corner, 1200MHz and 1333MHz in the near future.
RD-RAM is, arguably, the fastest type of memory available.
A computer needs 2-4 pieces of RD-RAM to get the best performance, (or, as in the case of the old style of RD-RAM, to work at all).
An RD-RAM computer also needs "continuity RIMMs" filling any empty memory slots.
RD-RAM is the most expensive type of memory available. (for a home PC)

Designation:		Bandwidth(speed):
PC400		800MB/s
PC600		1200MB/s
PC800		1600MB/s
PC1066		2132MB/s
PC1200		Up to 10.6GB/s

So there you have it, a rough idea of the different types of memory options available for you to choose from.
I hope I didn't bore you or confuse you more than you were, if you have any questions, corrections or comments, please feel free to email me.