Random-access memory
lastmod 2024-12-18created 2015-10-055 edits
In computing, random-access memory (Random Access Memory, random-access storage device; North Korean terms: 'free memory device', 'read-write memory device', 'free-access memory device'), or RAM, is main memory that can access any region to read and write. It is made of semiconductor circuits. RAM is commonly understood to mean ‘memory that can be read and written’, but this is a misconception. RAM gets the name ‘random’ because it takes the same amount of time to access (read and write) data stored at any location. By contrast, magnetic disks such as hard disks and floppy disks, and magnetic tape, take different amounts of time to access depending on where the data is stored.
Data retention time after power-off
Since DRAM must be refreshed periodically to retain data, this post describes an experiment to measure how long it takes for RAM data to be lost after a computer is powered off.
Test environment
- NovaCustom laptop with DDR5 SODIMM
- Desktop with an MSI PRO Z790-P WIFI board and DDR4 DIMM
- Temperature kept at 19-20°C, humidity at 33%
Test results
- DDR5 laptop
- Most data lost within 1 second of power-off
- Even in the best cases, bit change rates of 36.06%, 39.28%, and 41.04% were recorded
- DDR4 desktop
- Data retention time was much longer
- Right after power-off: 0.08% bits changed, after 10 seconds: 6.32% bits changed, after 2 minutes: about 49.51% bits changed
- Effect of DIMM topology
- DDR5 - similar change patterns between bits 0-31 and 32-63
- DDR4 - clear differences observed between consecutive 8-bit groups
Conclusions and implications
The exact cause of the differences still needs to be identified and tests need to be run on more platforms, but
- RAM data does not disappear immediately after power-off
- Data retention time varies greatly depending on DDR generation and hardware configuration