Asynchronous DRAM

Asynchronous DRAM is an older type of DRAM (dynamic random-access memory) used in the first personal computers. It is called "asynchronous" because memory access is not synchronized with the computer system clock. Modern PCs use SDRAM (Synchronous Dynamic Random-Access Memory) that responds to read and write operations in synchrony with the signal of the system clock.

Why was it phased out?

When a program issued an instruction to access data in asynchronous memory, the data was still accessible on the system bus some time later. When the data was accessed later, it was variable and not guaranteed. This was acceptable on older systems, until they reached speeds of about 66 MHz.

Asynchronous, Memory terms, MHz, Personal computer