Magento 2 – folder structure is having lot of changes compared to magento 1.x
Below magento 1.x folders are located into single folder called dev in magento 2.X ( root/pub)
Magento 1.X
1. root/errors
2. root/Js
3. root/media
4. root/skin
Under the pub folder you may get all the these files.
1. Js, Css, Images folder are located into pub/static/adminhtml(for backend related files) and pub/static/frontend (for frontend files)
2. Shell folder – In magento 2.X shell folder is available from root/dev. Basically dev folder is having migration related files.
3. Setup directory is for installation process
4. cron file is moved to pub folder.
5. index file is moved to pub folder.
6. app/code/core, /local, /community folders are removed in Magento 2.x And the structure is root/app/code/Namespace/Module