RAM the full story

Matt555

http://www.hardwareforums.com/memory...xplained-6455/
That should give some good information on latencies of RAM. Very good article.

__________________

Addis

That doesn't explain fully, only a breakdown of latencies. The reason RAM is required is to provide a place for programs and temporary data which the CPU is operating on to be held. For example an instruction for the CPU to add 2 values together and store it in a variable would require a range of memory addresses equal to the size used by the data type of the variable.

Executing programs from the hard drive just isn't possible because the hard drive is not random access, rather it has moving parts that must read magnetic values.

DRAM works by using one capacitor and a transistor to create a charge 'bucket'. This bucket has a hole in it which means that it constantly has to be refreshed for it to maintain a charge. So a stick of DRAM has millions of these capacitor/transistor pairings to hold the data. They are organized into logical rows and collumns, which is how they can be accessed in a random order.

Traditionally, the RAM is operated by a memory controller usually located on the Northbridge chip. This controller will take requests for data in memory frm the CPU via the address bus, access the RAM, and then send the data to the CPU via the data bus.

Another type of RAM is called static RAM (SRAM) and it works differently to DRAM. SRAM uses a number of transistors in a flip flop array to hold data (transistor-transistor logic). Because of its lack of reliance on a capacitor, it can scale to much higher speeds than DRAM. However the drawback is that it takes much more space than DRAM circuitry, and because of this and extra components requires is more expensive. So its only used on the cache on a CPU or where extremely fast RAM is required.


RAM like all other components has brands which are better than others. Manufacturers like Geil, G.Skill, Corsair, OCZ etc provide RAM of a higher quality than normal generic modules. Their modules may be far more defect free, and may be able to operate under higher voltages. Also they can be overclocked better than some generic modules.

__________________
Never trust a program you don't have the source code for.

My website | Powerful Desktop Linux | Linux for human beings | Linux for power users | Linux for ricers

Matt

Thanx. That was very intresting. How does the page file work then

So if i have ddr400 and someone els has say ddr320(whateva the number) which is better/faster. What im asking is for the significance of the number after the ddr.

Matt555

The number after the DDR part dictates it's speed.

DDR266 = 266MHz (133MHz x 2 because of Double Data Rate - DDR)
DDR333 = 333MHz (166MHz x 2 because of Double Data Rate - DDR)
DDR400 = 400MHz (200MHz x 2 because of Double Data Rate - DDR)

So DDR400 is faster than DDR333, DDR333 is faster than DDR266.

__________________

Addis

The swap file (pagefile in windows) usually works like this:
You have a number of small programs open, and start a large one like Photoshop with low RAM. The programs that aren't being used which are idle are loaded into the swap file and then frees up RAM needed for the larger program. When you switch to the smaller one, it swaps another program into the RAM and retrieves the program from the swap file.

This usually happens when you're playing a game. You can exit the game and for a while you have high HD activity as utilities and other programs loaded into the swap are put back into the RAM.

Your RAM will operate at the highest its rated for and the highest your bus supports. So if you have a 200MHz bus, then your motherboard can support DDR400 (PC3200) RAM. If your motherboard only supports 166MHz FSB then the fastest RAM you can fully use is DDR333(PC2700).

You can buy faster RAM than your motherboard supports or is currently operating at, however the RAM will slow down to the maximum bus speed so unless you overclock theres no advantage.

__________________
Never trust a program you don't have the source code for.

My website | Powerful Desktop Linux | Linux for human beings | Linux for power users | Linux for ricers

Matt

thanx again. Your depth of knowledge on everything ive asked is amazing.