Ram Questions - What does it all mean?

[jcbray]

ECC is an error correction RAM...so if something goes wrong and data in the RAm changes, it is fixed up...makes it more stbale, but more slow.

the numbers you quoted 5-5-5-12 are latencies (speed sort of) the lower the number, the lower the latency. Lower latency means faster speed...

[axsys]

ok, that helps clear thinks up a bit. thanks alot jcbray.

[irieken]

I know that the person before me already answered your question, but I figured that I'de post a response for other readers looking for RAM information (and clarify the first person's response a little bit).

ECC RAM has an extra parity bit for every 8 bits of data. This allows the RAM to add up all the 1s in each byte of data and storing whether it is even or odd in the parity bit. When the data is being copied out of RAM, the number of 1s are added up again and checked against the parity bit to see if there was an error. This does not slow down performance.

Registered memory has extra buffer circuitry that allows it to hold data before moving data in/out. This is great for machines that need a lot of memory modules, because it doesn't strain the memory controllers nearly as much. However, registered memory holds the data in its registry for a clock cycle, which means that it will decrease memory speed.

As for the timings, there are generally four numbers given. In order: these are the CAS latency, RAS to CAS delay, RAS precharge, and the Act to Precharge delay.

The CAS is the time that it takes for a Column Access Strobe. This is how long it takes to verify that the address column is valid. Lower is better.

RAS to CAS measures the number of cycles it takes to go from checking row to column. The speed of this timing doesn't influence performance by very much. Lowe is always better though.

RAS Precharge is the amount of time between a Row Address Strobe and Precharge... Lower is better.

And the last timing is how long it takes for the RAM to go from activity to being clear of the operation. Definitely lower is better.

So, get the highest frequency memory that your machine supports, and aim for the RAM with the lowest timings.

[axsys]

thank irieken, thats some great information. so, for modeling, which kind of ram would be best? ecc and unbuffered?

[Sp1ice]

thank irieken, thats some great information. so, for modeling, which kind of ram would be best? ecc and unbuffered?

It depend on your Machine/motherboard.. some machines can only use ECC (Opteron and Xeon systems normally) and some will only work with Unbuffered.. if you have a machine already check your documentation or contact the manufacturer to find out what works.

Personally if you are just modelling.. Unbuffered is fine.. when you get into rendernodes / server side applications you would want ECC.

[axsys]

ok. thanks for all the help guys. now i have an idea what to look for in terms of memory for my new computer.

[irieken]

It depend on your Machine/motherboard.. some machines can only use ECC (Opteron and Xeon systems normally) and some will only work with Unbuffered.. if you have a machine already check your documentation or contact the manufacturer to find out what works.

Personally if you are just modelling.. Unbuffered is fine.. when you get into rendernodes / server side applications you would want ECC.

I agree. Tell us what kind of hardware you are running/planning to run, and we'll try to set you in the right direction.

Athlon and Athlon 64 systems are usually well paired with PC3200 DDR memory. Corsair makes RAM that almost all motherboards like.

[lots]

Well most likely you wouldnt have a choice in your new system of wheather or not to get ECC or non-ECC memory.

Basically, if you pick an Athlon64 (including the X2) OR a Pentium 4/D/EE (whatever else pentium) you will be limited to non-ECC memory only. If you buy the Opteron, you can ONLY buy ECC memory. The Xeon is different. Unlike the Athlon64 and Opteron, its memory controller is not onboard, thus some Xeon motherboards support non-ECC while others require it. Generally speaking, non-ECC memory is faster and cheaper, but more prone to errors than ECC.

ECC matters in the server world. If you do not plan on serving out massive ammounts of data, and have an uptime of 99.9999% of the year, dont worry about getting ECC. You will only be forced to use ECC if you buy an Opteron or a the very early versions of the AthlonFX (among the chips I mentioned).

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