"Sudden Power Outage? Data Remains Intact"…World's First Non-Volatile PC Developed

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[Asia Economy Reporter Kim Bong-su] KAIST announced on the 25th that Professor Myungsoo Jung's research team from the Department of Electrical and Electronic Engineering has developed the world's first hardware and software technology that stops computer time, called the "Lightweight Persistence Centric System (Lightweight PC, LightPC)."

All information at the moment when the computer's time is stopped (execution state and data) is maintained regardless of power supply, and all maintained information can be immediately restored and operated whenever the user desires.

Existing computers use volatile memory, DRAM, as the main memory, so when power is lost, the data stored in the memory is lost. Non-volatile memory (such as Intel's Optane memory), which consumes less power and offers larger capacity than DRAM, has the characteristic of permanently retaining data. However, due to slow performance caused by complex internal structure design, it cannot be fully used as main memory and is used together with DRAM to selectively maintain only some data stored in the non-volatile memory.

Even if the performance of non-volatile memory improves under ideal conditions and it is used solely as main memory, it cannot maintain all information of the computer in the event of sudden power loss. This is because volatile components inside the non-volatile memory and temporary storage areas such as registers or cache memory (volatile) within the processor itself cannot be continuously preserved without power supply.

Due to these issues, to maintain execution state and data in existing computers, checkpointing techniques that move volatile state data, including DRAM and processor-held data, to non-volatile memory or storage devices like SSDs are used in data centers and high-performance computers. However, checkpointing consumes additional time and power for periodic data transfer and has the critical drawback of requiring a full system reboot and data recovery process after power is restored following a blackout.

The LightPC developed by the research team eliminates these processes by developing processor, memory controller, and operating system technologies that can maintain all program execution states and data non-volatilely without power. To achieve this, the team configured the system using only persistent memory without existing memory or storage devices, maintaining most system states non-volatilely. Immediately after power loss, the system can stop computer time even during blackout by converting the processor's remaining non-persistent states into non-volatile states through a device triggered by the power supply unit's signal.

To this end, the LightPC technology developed by the team minimizes volatile components on the processor's hardware data path and simplifies the complex internal structure as much as possible. By maximizing data processing parallelism, performance was improved so that users do not feel a significant difference compared to high-performance systems using only DRAM in typical application execution. Additionally, to maintain consistency while stopping computer time, the team prevented arbitrary changes to states and data to avoid non-deterministic program execution and built an operating system with various persistence features added. Because consistency is maintained, when power is restored, the computer can resume execution from the stopped time without a boot process.

To verify the effectiveness of LightPC, the research team built a non-volatile computer by installing prototype persistent memory on a self-made system board and developed an operating system prototype that stops computer time during power outages, running it on the non-volatile computer. They confirmed that when power was randomly cut off during the execution of enterprise applications and then restored, all program execution and data were consistently recovered to the state just before power loss. Furthermore, LightPC demonstrated up to 8 times larger memory, 4.3 times faster application execution, and 73% power consumption reduction compared to existing computers.

Professor Myungsoo Jung said, "The developed non-volatile computer can provide large-capacity memory along with high reliability and service safety, which is expected to maximize carbon-neutral energy efficiency through low-power operation in data centers and high-performance computing." He added, "It is also expected to be widely used in minimizing battery usage in vehicles, mobile phones, Internet of Things devices, and achieving a hyper-connected society."

Meanwhile, this research will be presented under the paper title "LightPC" at ISCA 2022 (International Symposium on Computer Architecture), the top academic conference in computer architecture, to be held in New York City this June.

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