RAM revealed

Memory Research

Article from ADMIN 06/2011

By Werner Fischer

Virtualized systems are inflationary when it comes to RAM requirements. Storage access is faster when excess RAM is used as a page cache, and having enough RAM helps avoid the dreaded performance killer, swapping. We take a look at the current crop of RAM.

Random Access Memory (RAM) has always been used by processors and computer systems to store the programs currently being executed along with their data. Back in the 1980s, operating systems started to use excess RAM as a page cache for caching disk access [1].

The technology used since the start of the millennium, however, is Double Data Rate Synchronous Dynamic Random Access Memory (DDR-SDRAM) [2]. In contrast to its predecessor, SDRAM, DDR-SDRAM transfers data on both the rising and falling edges of the clock signal, thus doubling the data rate.

DDR-SDRAM has reached the third generation now, and work is in progress on the fourth (Table 1). Current systems use DDR3; but, because servers and desktops are typically deployed for three to five years, many datacenters and offices still use DDR2 RAM. Initial prototypes of DDR4 also exist. However, because the energy efficiency of DDR3 continually improves and Load-Reduced (LR)-DIMMs will support even larger DDR3 memory configurations in future, analysts don't anticipate a significant breakthrough for DDR4 until 2014.

Table 1

DDR Generations