Types of ram memory

Memory Terminology: This is a simplified overview of RAM terms and definitions

100 pin memory
Used primarily in laser printers, 100 pin SIMM memory is not compatible with other formats.

CAS Latency:
To oversimplify a complex discussion, the main timing of a RAM module is described by a CAS (Column Address Strobe) Latency value. This is the length of time that a RAM module needs between serving one request and when it is “recharged” and able to take the next request. All else being equal, and if the motherboard can make use of faster latencies, the lower the CAS Latency value the faster the RAM can respond.

Typical DDR CAS values are CL3, CL2.5 and CL2 . There are other latency measurements but CAS Latency is the most important.

In older SDRAM (PC66, PC100, PC133) , a CL2 module is not always faster than a CL3 module – the effective speed is determined by the memory controller on the motherboard of the computer, and in some cases a CL3 module matches an older motherboard’s timing better and performs faster than a CL2 module.

Non-Synchronus memory isn’t measured the same way – it has a memory response speed in nanoseconds, and the computer waits for the RAM chip to be ready. Synchronous RAM, in contrast, synchronizes its operations to the computer’s memory buss clock.

SDRAM can be CAS 2 or CAS 3

DDR RAM is normally CAS Latency 2.5 for PC2700 modules and CL3 for PC3200 modules. Premium modules are available with CL2.5 or CL2.0 on higher-capacity PC3200 modules. (DDR make two operations per clock cycle, which is why it can have “half” of a tick)

DDR-2 RAM is normally CAS Latency 4 (DDR2-533), CAS Latency 5 (DDR2-667) and CAS Latency 5 0r 6 (DDR2-800). Lower latency RAM is available at higher prices.

DDR-3 RAM has CAS latencies in the range of 7 to 9. This means that the latency penalty versus DDR-2 RAM negates some of the advantage of DDR-3 running at higher clock speeds. This is expected to improve over time.

DDR – Dual Data Rate RAM
Can be packaged in both DIMM (184-pin for Desktops) and SO-DIMM (200-pin for laptops) forms. Speeds are PC2100 (266 MHz) PC2700 (333 MHz) and PC3200 (400 MHz) DDR . The standards for speeds higher than PC3200 are not finalized, although some manufacturers offer “PC3700″ “PC4000″ and up DDR modules as a marketing designation.

DDR-2 A format that is faster than DDR. DDR and DDR-2 are not compatible with each other. Designations are PC2-5300 (DDR2-667 MHz), PC2-4200 (DDR2-533 MHz, also called by some manufacturers PC4300), and PC2-6400 (DDR2-800). Available in both DIMM and SODIMM packages. Faster speed RAM is available at higher prices.

DDR-3
DDR-3 is now the primary RAM type for new desktop and laptop machines and motherboards. DDR, DDR-2 and DDR-3 are not compatible with each other. Some early DDR3 motherboards have sockets for both DDR-2 and DDR-3 memory, however the two formats cannot be combined at the same time.

DDR-4
New type of memory.There are a lot of deeply technical aspects to DDR4, but we won’t dive that far. The two key improvements in DDR4 are power consumption and data transfer speed, thanks to the development of an all-new bus.

DDR4 memory will deliver significant benefits in terms of performance and power consumption. 

DDR3 generally requires 1.5 volts of electrical power to operate. DDR4 needs 20 percent less—just 1.2 volts. DDR4 also supports a new, deep power-down mode that will allow the host device to go into standby without needing to refresh its memory. Deep power-down mode is expected to reduce standby power consumption by 40- to 50 percent.