Comparing computer memory types

Several technologies are grouped under the heading of computer memory, and they differ in how they store bits, how fast they operate, and where they are used. The main working memory of a PC is dynamic RAM (DRAM), which stores each bit as a charge on a tiny capacitor. Because that charge leaks away, the memory must be refreshed many times a second, and the design favours high capacity at low cost rather than the very fastest access, which is why it serves as the bulk of system memory.

DRAM has been refined through successive generations. Synchronous DRAM (SDRAM) ties its operation to the system clock for more orderly, faster transfers. Double data rate memory, beginning with DDR and continuing through DDR2 and DDR3, transfers data on both edges of the clock and, with each generation, increased speed and efficiency while lowering operating voltage. The Rambus design, RDRAM, was a competing high-speed approach used in some systems before the DDR family became dominant.

Not all memory is volatile working storage. Flash memory retains its contents without power and can be electrically erased and rewritten, which makes it suitable for solid-state drives, memory cards, and USB keys rather than for main system memory. Comparing these types comes down to trade-offs: dynamic RAM and its DDR variants offer the speed and capacity needed for active work but lose data when switched off, whereas flash sacrifices some speed and endurance for the ability to keep data permanently.

Frequently asked questions

What does DDR memory do differently?

Double data rate memory transfers data on both the rising and falling edges of the clock signal, effectively doubling throughput compared with transferring on one edge, and later generations improved speed and lowered voltage.

How does flash memory differ from DRAM?

Flash memory keeps its contents without power and is used for storage like USB keys and solid-state drives, whereas DRAM is faster volatile working memory that loses its data when switched off.

What was Rambus RDRAM?

RDRAM was a high-speed memory design from Rambus used in some computers as a competing approach before the DDR family of memory became the mainstream choice.