SRAM and DRAM are common types of RAM. Most users with modern computers will be familiar with DRAM. SRAM uses a data storage scheme called a flip flop. DRAM stores data differently, in a cell that consists of one capacitor and one transistor. The transistor reads the state of the capacitor, which stores the bit (1 or 0) and allows that bit to be changed as necessary. You’ll be much more familiar with DRAM for one very important reason: it’s less expensive to produce than SRAM.
Both of these types of RAM differ from PRAM in one important regard: DRAM and SRAM are volatile. This means that, when you cut the power to the chips, the data is lost. PRAM is non-volatile, allowing the data stored on them to be held if the power is cut.
SDRAM is what you’ll generally see on the market today. The acronym, because it appears to be a combination of static and dynamic might be a bit confusing. It actually stands for Synchronous DRAM, referring to the way that the data is access on the chip. It is a very fast form of RAM. Data access rates have been expanded over the years, and this is denoted by the acronym DDR. DDR is double the data rate of standard SDRAM, DDR3 and forward continue to increase the speed of RAM.
High-end machines tend to utilize the fastest RAM available. You’ll see this in machines designed for gaming and graphic design, in particular. Machines that are used for processing video and audio are also oftentimes outfitted with very fast and high-capacity RAM. Computers that are used for more general purposes—word processing etc.—generally don’t need to have the highest speed RAM.