RAM; Random Access Memory, is temporary computer memory held on microchips available for use by programs on a computer. Instructions and data are held in RAM while the computer is in use and disappear when turned off. The more RAM a computer has, the more applications a user can run simultaneously. Also referred to as “main memory”.
The processor also has its own memory known as the L2 cache, the cache lies between the processor and the RAM. The processor sends and retrieves data from this cache, when this cache overflows data is sent to the RAM.
There are five types of RAM; SD, DDR, DDR2, DDR3 and DDR4. They differ in the way they operate and mainly in their operation speeds. All RAM’s used in computers today have a synchronous interface meaning they wait for a clock signal before it can respond to clock signals.
SDRAM stands for Synchronous Dynamic Random Access Memory, is Single Data Rate meaning that SDRAM can accept one command and transfer one word of data per clock cycle. As mentioned above SDRAM’s have synchronous interface therefore they depend on the computer clock signals to perform operations. Typical speeds of SDRAM are 100 and 133 MHz.
DDR SDRAM stands for, Double Data Rate Synchronous Dynamic Random Access Memory. DDR RAM transfers data twice per clock cycle, hence the name double data rate. DDR clock speeds range between 200 MHz (DDR-200) and 400 MHz (DDR-400). DDR-200 transfers 1600 MB/s, while DDR-400 transfers 3200 MB/s.
DDR2 SDRAM stands for Double Data Rate 2 Synchronous Dynamic Random Access Memory. DDR2 is twice as fast as DDR which means twice as much data is carried to the module for each clock cycle. Also due to the design improvements DDR2 consumes less power as compared to the DDR memory. DDR2 speeds range between 400 MHz (DDR2-400), 800 MHz (DDR2-800) and 1066 (DDR2-1066). DDR2-400 transfers 3200 MB/s. DDR2-800 transfers 6400 MB/s. DDR2-1066 transfers 8533 MB/s.
DDR3 SDRAM stands for, Double Data Rate 3 Synchronous Dynamic Random Access Memory. DDR3 is supposed to act twice as fast as DDR2 memories. Thus DDR3 speeds range between 800 MHz (DDR3-800), 1600 MHz (DDR3-1600) and 2133 MHz (DDR3-2133). DDR3-800 transfers 6400 MB/s; DDR3-1600 transfers 12800 MB/s and DDR3-2133 transfers 17066 MB/s.
So by now after reading the above it is quite obvious what DDR4 SDRAM stands for, Double Data Rate 4 Synchronous Dynamic Random Access Memory. In theory DDR4 is supposed to act twice as fast as DDR3 memories. Thus DDR4 speeds range between 2133 MHz (DDR3-2133) and 4266 MHz (DDR3-4266). DDR3-800 transfers 17066 MB/s and DDR4-4266 transfers 34133 MB/s.
There is a difference at the physical level too. You buy memory chips already soldered on a printed integrated circuit boards called a “memory module”. Memory modules for each DDR generation are physically different, so for example you won’t be able to install a DDR3 module in a DDR4 socket. Unless your motherboard supports both DDR3 and DDR4 sockets (only a few do), so you cannot upgrade from DDR3 to DDR4 without replacing the motherboard and eventually the CPU. The same thing is valid with DDR, DDR2 and DDR3. DDR2 and DDR3 modules have the same number of pins, however, the key notch is placed in a different position.
All DDR2, DDR3 and DDR4 chips use BGA (Ball Grid Array) packaging, while DDR chips almost always use TSOP (Thin Small-Outline Package) packaging. There are a few DDR chips with BGA packaging on the market (like the ones from Kingmax), but they are not so common.
DDR chip with TSOP packaging below
DDR2, DDR3 and DDR chips with BGA packaging below
I hope that this article helped you to understand the RAM comparison for SD, DDR, DDR2, DDR3 and DDR4. Feel free to share your thoughts about this article using the comments section below or catch us on Twitter.