Universal memory

Universal memory refers to a hypothetical computer data storage device combining the cost benefits of DRAM, the speed of SRAM, the non-volatility of flash memory, and infinite durability. Such a device, if ever it becomes possible to develop, would have a far ranging effect on the computer market.

Computers for most of their recent history have depended on several different data storage technologies simultaneously as part of their operation. Each one operates in a place where another would be unsuitable. A personal computer might include a few megabytes of fast but volatile and expensive SRAM as a CPU cache, several gigabytes of slower DRAM for program memory, and multiple hundreds of gigabytes of the slow but non-volatile flash memory or a few terabytes of "spinning platters" hard disk drive for long term storage. For example, UC San Diego recommended students entering in 2015–2016 have a PC with:

- a CPU with a 4×256 KB L2 cache, and a 6 MB L3 cache

- 16 GB DRAM

- 256 GB solid-state drive, and

- 1 TB hard disk drive

Researchers seek to replace these three different memory types with one single type to reduce costs and increase performance.

For a memory technology to be considered a universal memory it would need to have characteristics from several different common storage technologies. It would need to:

- operate very quickly – like SRAM cache

- support a practically unlimited number of read/write cycles – like SRAM and DRAM

- retain data indefinitely without using power – like flash memory and hard disk drives, and

- be sufficiently large for common operating systems and application programs, yet affordable – like hard disk drives. (For 2015, UCSD judged 1 TB as "sufficiently large but affordable".)

Many types of memory have been researched in the hopes of creating a practical universal memory type. These include:

• magnetoresistive random-access memory (MRAM)
• bubble memory (1970s and 80s)
• racetrack memory
• ferroelectric random-access memory (FRAM)
• phase-change memory (PCM)
• programmable metallization cell (PMC)
• resistive random-access memory (RRAM)
• nano-RAM
• memristor-based memory

For various reasons, none have yet achieved all these goals.