Does the Mycroft device support DDR 512M devices ?
It can run in that amount but loading skills or any memory intensive effort will start to bog things down fast.
What is the ideal recomend DDR size ?
at least 1 gb of ram
As @baconator said, it will work but you will need to have a swap configured (like a USB flash drive) because the SD card will be too slow to handle this task.
Here is the current memory usage of my instance running in Docker with 35 skills.
pi@rpi402:~ $ free -m total used free shared buff/cache available Mem: 3617 496 2573 1 547 3043 Swap: 99 0 99 pi@rpi402:~ $ docker ps -a CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES c7e6371db118 smartgic/mycroft-api:latest "uvicorn app.api:app…" 2 weeks ago Up 7 minutes mycroft_api cff38462b257 smartgic/mycroft-voice:latest "python -m mycroft.c…" 2 weeks ago Up 7 minutes mycroft_voice eaf5b5adb6c9 smartgic/mycroft-skills:latest "python -m mycroft.s…" 2 weeks ago Up 7 minutes mycroft_skills aebfa71bb9a8 smartgic/mycroft-audio:latest "python -m mycroft.a…" 2 weeks ago Up 7 minutes mycroft_audio 8f82c0b1340b smartgic/mycroft-cli:latest "sleep infinity" 2 weeks ago Up 7 minutes mycroft_cli b031984f5f43 smartgic/mycroft-enclosure:latest "python -m mycroft.c…" 2 weeks ago Up 7 minutes mycroft_enclosure 142e7d56228d smartgic/mycroft-bus:latest "python -m mycroft.m…" 2 weeks ago Up 7 minutes mycroft_bus
|mycroft-audio-record|[installed]| |mycroft-spelling|[installed]| |mycroft-npr-news|[installed]| |mycroft-timer|[installed]| |mycroft-date-time|[installed]| |mycroft-reminder|[installed]| |mycroft-playback-control|[installed]| |homeassistant|[installed]| |camera|[installed]| |mycroft-personal|[installed]| |fallback-unknown|[installed]| |homescreen|[installed]| |mycroft-stop|[installed]| |mycroft-hello-world|[installed]| |mycroft-speak|[installed]| |mycroft-alarm|[installed]| |fallback-wolfram-alpha|[installed]| |mycroft-configuration|[installed]| |skill-time.mycroftai|[installed]| |mycroft-installer|[installed]| |mycroft-support-helper|[installed]| |mycroft-version-checker|[installed]| |mycroft-mark-2|[installed]| |mycroft-singing|[installed]| |mycroft-joke|[installed]| |mycroft-volume|[installed]| |mycroft-fallback-duck-duck-go|[installed]| |skill-date.mycroftai|[installed]| |mycroft-ip|[installed]| |mycroft-pairing|[installed]| |mycroft-naptime|[installed]| |fallback-query|[installed]| |mycroft-wiki|[installed]| |mycroft-sonos-controller-skill.smartgic|[installed]| |mycroft-weather|[installed]|
Its better to have more ram but the Zero2 is a great price but likely the 2gb Pi4 is the best option.
Zram or zswap is a great addition still add a swap file of same size though so that if it hits already compressed data (uncompressable) it will not fail but just use a lower order backup swap device.
In normal running the file swap will never be touched but quite often installs and compiles contain compressed data that will cause swap to fail if there is no backup to the compressed memory.
I have found that a copper shim under a heatsink makes it much easier to get 1.4Ghz on a Zero2 must be fast heat transients as overall it runs no cooler but found them much easier to hit and stay stable at 1.4Ghz, so with zram and a bit of an OC a Zero2 could still be an option.
I did some scripts as the standard debian/ubuntu ones hark back to 1st release and ignore a few elements of zram.
Do a google for a zram or zswap utility or use the above as the distro based ones are very simple and also strangely outdated.
PS as utilities go https://github.com/ecdye/zram-config now supported by the Home Assistant guys is very comprehensive.
It allows you to create zram drives that can be great alternatives to folders such as \var\log in zstd compressed ram and reducing sd-card / emmc writes to practically none.
Also it can load the whole root as part as an overlayfs and use zram as an upper so that all writes take place in memory and merges down on shutdown.
So its write once on shutdown and covers the whole OS so is an amazingly low write scheme and also persistent.