Everything you wanted to know about RAM
I am not a RAM (Random Access Memory) expert. However, after all the research I have just completed, I have learned a great deal about RAM. I thought I would share with you some of what I have learned about DDR, SDRAM, and RDRAM, and try to put it all in simple language.
As I have mentioned in some earlier newsletters, I have been putting together 5 new computers for my office. Two of them are identical machines, and almost all of them had some piece of defective hardware that I just purchased. After getting 4 of the 5 machines up and running, two of the computers, which are identical machines, started to reboot unexpectedly and occasionally crash. I checked the BIOS settings, and everything else, thinking it must be the RAM I just purchased. It was Samsung 256M, one stick for each machine. Having received one defective stick already, coupled with the problems I was experiencing, the RAM was my first suspect.
I was getting the same type of errors, an assortment of file errors, almost never the same file or VXD involved. So for my first test, I switched the slot that the stick of memory was in, my machine will accept up to 3 sticks. Nothing changed, which ruled out a bad motherboard. Next, I decided to put both sticks in one machine; this appeared to fix the reboots and crashes. I moved both sticks to the other machine and it also stopped spontaneous rebooting. I decided to do some research about DDR RAM. I recalled reading on an internet bulletin board, that if your stick of RAM has chips only on one side, then you need to install RAM in pairs. After further investigation however, I learned that you do not need a pair of RAM for DDR and SDRRAM,where as EDO RAM and RDRAM do require a pair. If you are experiencing similar problems pay close attention.
EDO RAM is the older 72 pin stick found in computers when the Pentium first came out, after the 486. RDRAM also known as RAMBUS, is the Rolls Royce of RAM, very expensive and not used much since about 2002 when DDR RAM came out. By the way, I recently rumor heard that Dell wants to start using it again for Vista. The SDRAM and DDR RAM are very similar and are not required to be installed as pairs, and you can also use 2 different sizes: 1 - 128megs and 1 - 256megs, etc. In any respect, if you have one type of RAM (I.E. DDR) you cannot replace it with a different type of RAM (I.E. SDRAM), as the slots that they fit into are different. DDR2 is currently the newest type, 240 pins.
SDRAM is Single DATA RAM - 168 pin, while the DDR SDRAM is Double Data Rate RAM - 184 pin, SO-DIMM DDR RAM is 200 pin. Although DDR and SD RAM are basically the same (except for the size and pin count), the DDR is twice a fast as the SDRAM, not just in nanoseconds, but also in data throughput. Anyway, how fast is a nanosecond, can anyone show me how fast that is? If your RAM is 8 nanoseconds and you replace it with 7 nanosecond RAM you will have pushed the data through the RAM 1 billionth of a second faster, not quite worth the investment.
RAM has clock cycles, a rise and a fall, it also has a timing. SDRAM comes as 2 or 4 clock cycle. 2 clock cycle accesses 2 chips per cycle on the stick at a time and only is used with 66 MHz, while 4 clock cycle accesses 4 chips per cycle. There is also PC100 and PC133, types of SDRAM. PC100 can only run at 100 MHz while PC133 can run at 100 or 133 MHz, 133 is faster. Now, before you buy any RAM check your motherboard documentation.
DDR comes as DDR200 or PC1700 - which is 200 Mhz; DDR266 or PC2100 - 266Mhz; DDR300 or PC2400 - 300Mhz while PC2700 runs at 333Mhz; DDR400 PC3200 - 400Mhz; DDR500 PC4000 - 500Mhz.
DDR2 comes as DDR2 PC 2700 to PC 8000 which runs at an even high Mhz
You need to check your motherboard to see what type it will accept. But here's the catch, the 200Mhz is really running at 100; the 266Mhz is running at 133Mhz, the 300 MHZ at 150 Mhz. Our BIOS must be set for the DRAM Frequency to 266 in order for the RAM to run at 133. Oh, and by the way, that RAMBUS RAM runs at 800Mhz! If your RAM is not listed here, it was not available at the time of this writing.
If you are going to add additional sticks there is no need to purchase PC133 if your current stick is PC100. Your motherboard will always process the data at 100 MHz, at the slower speed. But you can tweak this a little with the CAS (Column Address Strobe) if it's an available option in your BIOS. You can use a setting of 2 instead of the default 3 in the BIOS, this will use only two clock cycles for the initial data instead of 3.
When you go to buy RAM and you see 16X64, this means 16 Meg X 64 Bits which is a 128 Meg stick of RAM. A stick of RAM that is ?x64 is non error correcting, while a stick of ?x72 is error correcting and runs slower that the 64. ECC RAM (error correcting code) is normally used on a server motherboard for more reliability and costs more, the extra 8 Bits is used to correct the data passing through. Your motherboard probably cannot use ECC RAM and if it able to use ECC RAM it cannot be combined with NON ECC RAM. ECC is parity RAM, Non-ECC RAM is Non-parity RAM. Most types of RAM come in either NON ECC or ECC.
Double sided RAM, or single sided RAM, makes no difference. By "sided", I mean if your stick has chips on one side or both.
I think I have covered all the basics, so now let me finish my story about my reboots. Well, after my research, I went back through all my settings in the BIOS and remembered that I did not use the Auto and SPD setting in the BIOS. I had originally set them up manually so that I could over clock the CPU. I had set the CPU to DRAM ratio to 1:1 and had raised the CPU Clock to 116 Mhz without changing the multiplier; I am running a 8000 RPM CPU cooler to handle the heat, it's loud. My thought at the time, was that I have DDR266 RAM and a setting of 3:4 ratio may be too much for the DDR.
My calculation was that at 3:4 the RAM would be running over 200 MHz, and a slower speed of 116 Mhz would not hurt the RAM.
I learned that by cutting back on the power to the RAM slowed the system down more then the 4 or 5% I had gained by over clocking the CPU. I remember reading that the difference of a 10% increase of the CPU (500 MHz to 550 Mhz) results in only a 2% increase in speed, while a $40.00 stick of the correct RAM will increase your speed about 8 or 9%.
I found out that in most cases, the best performance of your RAM is obtained by putting the largest stick in slot 0, the next largest in slot 1, the smallest in slot 3. I also learned that I just spent $80.00 needlessly on two additional sticks of RAM to fix a problem that I created by attempting to over clock the CPU. Does anyone buy a couple of pieces of software so I can pay for the RAM I don't need, else I'll have to write it off as an expense to writing this page. I'll bet if I wrote Samsung, Crucial, or even Kingston they would have donated the RAM.
The moral of this story is, you would not soup up the family car to enter a NASCAR race and expect to even finish the race, ... or would you?