DRAM (dynamic random access memory)

Dynamic random access memory (DRAM) is a common type of random access memory (RAM) used in personal computers, workstations and servers.

Dynamic random access memory (DRAM) is a type of memory that is typically used for data or program code that a computer processor needs to function. DRAM is a common type of random access memory (RAM) used in personal computers (PCs), workstations and servers. Random access allows the PC processor to access any part of the memory directly rather than having to proceed sequentially from a starting place. RAM is located close to a computer’s processor and enables faster access to data than storage media such as hard disk drives and solid-state drives.

DRAM stores each bit of data or program code in a storage cell consisting of a capacitor and a transistor, and is typically organized in a rectangular configuration of storage cells. A DRAM storage cell is dynamic in that it needs to be refreshed or given a new electronic charge every few milliseconds to compensate for charge leaks from the capacitor.

DRAM is one option of semiconductor memory that a system designer can use when building a computer. Alternative memory choices include static RAM (SRAM), electrically erasable programmable read-only memory (EEPROM), NOR flash and NAND flash. Many systems use more than one type of memory.

DRAM image

The main advantages of DRAM are its simple design, speed and low cost in comparison to alternative types of memory. The main disadvantages of DRAM are volatility and high power consumption relative to other options.

There are many types or interfaces for communicating with DRAM. They include fast page mode DRAM (FPM DRAM), extended data out DRAM (EDO RAM) and synchronous DRAM (SDRAM). SDRAM is a generic name for types of DRAM synchronized with the clock speed of the microprocessor. They include single data rate (SDR) SDRAM, double data rate (DDR) SDRAM, DDR2 SDRAM, DDR3 SDRAM and DDR4 SDRAM.

DRAM vs. SRAM

DRAM is a successor to SRAM. Memory designers reduced the number of elements per bit and eliminated differential bit lines to save chip area to create DRAM. As a result, DRAM is less expensive to produce than SRAM.

But SRAM retains some advantages over DRAM. SRAM does not need to be refreshed because it operates on the principle of switching the current flow in one of two directions rather than holding a charge in place within a storage cell. SRAM is generally used for cache memory, which can be accessed more quickly than DRAM.

SRAM is capable of byte-level reads and writes, and is faster at reads and writes than DRAM. DRAM writes data at the byte-level and reads at the multiple-byte page level.

Power differences vary based on whether the system is in active or sleep mode. DRAM requires less power than SRAM in an active state, but SRAM consumes considerably less power than DRAM does while in sleep mode.

This was first published in May 2015

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