How do I interpret the specification of memory (RAM)?

Question

When looking at memory there are a few specifications that I don't understand and was hoping to have clarification on. What do these terms mean, and how do they affect the systems performance? Feel free to give technical data and answers to these, but not specific to the specs that I list as example below.

• Speed: DDR3 1600, DDR2 800
• Timing: 9-9-9-24 (what do each of the numbers mean?)
• Voltage: 1.5V (I know what voltage is, but how does it affect my system?)
• Multi-Channel Kit: Dual, Quad

Answer 1

Speed

The numbers are in MHz, and represent the frequency of the clock signal at which the RAM operates (x2 for DDR RAM, so DDR2-800 is running at 400MHz). The DDR means "Double Data Rate" which means it transfers data on both the rising AND falling edges of the signal (instead of just signal on vs. off). So, for example, DDR gives you the effect of 800MHz while actually still only being at 400MHz. DDR2 and DDR3 are superseding versions of the DDR spec. (ie: DDR3 is "double data rate type three").

Timing

Memory timings (or RAM timings) refer collectively to a set of four numerical parameters called CL, tRCD, tRP, and tRAS, commonly represented as a series of four numbers separated with dashes, in that respective order (e.g. 5-5-5-15). However, it is not unusual for tRAS to be omitted, or for a fifth value, the Command rate, to be added on (from Wikipedia).

CL (CAS Latency)

The CAS latency is the delay, in clock cycles, between sending a READ command and the moment the first piece of data is available on the outputs.

LRCD

Row Address to Column Address Delay - tRCD is the number of clock cycles taken between the issuing of the active command and the read/write command. In this time the internal row signal settles enough for the charge sensor to amplify it.

tRP

Row Pre-charge Time - tRP is the number of clock cycles taken between the issuing of the pre-charge command and the active command. In this time the sense amps charge and the bank is activated.

tRAS

Row Active Time - tRAS is the number of clock cycles taken between a bank active command and issuing the pre-charge command.

See here for more info on these and other RAM timing elements.

Voltage

The listed voltage is the minimum/recommended voltage required to power the RAM module. Not enough and it can't power the module, too much and you can damage the various chips on the module.

Multi-Channel Kits

These 'kits' are simply multiple single, similar (identical as possible) RAM modules packaged together. The intention (these days) is for them to be used in motherboards that have dual and triple (etc.) RAM channel capabilities. IE: since you need 2 sticks to do dual channel, and that became standard/regular for new systems a while back (before triple channel, quad, etc.), the memory manufactures started marketing their existing 'kits' as 'multi-channel kits'.

Previously the kits were sold mainly to give a bit of a break on price when buying multiple modules (ie: Two 1GB modules in a '2GB kit' is cheaper than buying two individual 1GB modules of the same model).

Answer 2

Speed:

The first part is the type of memory. DDR2 is Double Data Rate 2. The second is the speed in MHz that the memory operates at, in general the faster the better (to a point)

Timing:

The numbers are the number of wait cycles that must happen between different memory operations. Lower is better (more in depth).

Voltage:

The voltage that the memory operates at. In most cases this is just for reference but some systems require certain voltage memory. For example the new Intel core I chips need lower voltage (1.5v iirc) than the older Core 2 chips.

Multi channel:

Memory is sold either by the individual module (stick) or in kits for motherboards with multiple channels of memory. Most current boards have dual with the Intel socket 1336 have triple channel. All the packing does is make sure you are getting two of the exact same memory modules (same speed, timings, and size) which is required for multi channel RAM.