From According to information from GigaOM, Android 4.3 brought an important improvement to older devices, mainly by optimizing the system performance on Galaxy Nexus and Nexus 7 (first generation).
The magic happens because Google has included a fix that allows the operating system to manage and optimize flash memory, instead of letting data accumulate and slowing down depending on the use of the device.
“By invoking the TRIM command, the flash memory is optimized for input and output. Think of it as a Windows Disk Defragmenter that cleaned the file system and put pieces of files in order to speed up performance. TRIM has a similar concept, ”says the publication.
TRIM is triggered automatically, without the need for action by users, every 24 hours or when the device is active but not being used for an hour. The feature also works if the device has 80% battery or is being recharged and has at least 30% battery.
Note: The original GigaOM article only mentions the Nexus 7 but, in personal tests, the Galaxy Nexus also appeared to be faster (and with less crashes) than the previous version.