What is dynamic random access memory DRAM

SRAM (static RAM)

A Random Access Memory (RAM) is a volatile memory with random (random) access. It is the main memory of computers. Random Access Memories are available as Static RAMs (SRAM), which are static random access memories, and as Dynamic RAMs (DRAM), which are dynamic random access memories. Static RAMs are characterized by extremely short access times, consume less power than DRAMs and process the data synchronously with the bus cycle.

SRAMs are used in all caches, for example in level 1 caches, L2 and L3, and can receive the stored data without a classic refresh with periodic refreshment. In contrast to refresh technology, SRAMs work with a low quiescent current from a battery backup. The quiescent current accumulates over the many SRAM cells to form a higher current. The memory cells of SRAMs are addressed via their memory address.

Static RAMs use flip-flops as memory; In contrast, dynamic RAMs store the digital values ​​in MOS capacitors. Each individual bit is represented by a flip-flop. In this constellation, a transistor acts as a switch instead of the CMOS capacitor. It represents the positions "0" and "1". The stored data are not deleted when they are read out and are retained even after being called up. The memory cells can assume three different states: the standby mode, reading out and storing of data. Since SRAMs do not need a refresh, they are much faster than Dynamic RAMs (DRAM). The access time is in the range between 8 ns and 20 ns, the clock frequency is 500 MHz.

Special versions of the SRAM such as the PipelineBurst SRAM (PB SRAM) have access times of 4 ns to 8 ns and a burst cycle of 3-1-1-1 for bus speeds of 133 MHz. That means three clock cycles for the first and one clock cycle each for the following words.

SRAMs can be designed in ball grid arrays (BGA) with 85 pins and are used as level 1 cache.