The HP "456GB" is a 512 GB SSD. The 512GB is the unformatted size and some additional space is used for recovery.
The HP likely has 8GB of RAM but it could have more.
The iPad storage is similar to SSD storage space.
The Macbook with 256GB storage is an entry level model. It is fine if you don't store a lot on the Macbook this is usable. You may have to remove some programs to install others eventually, and this is not good for storing videos. If you plan on storing a lot on the Macbook, like all pictures from a family, videos or have lots of games and apps, then a larger storage solution would be needed.
8GB of ram is functional for most people. But this will not be good for large photo editing or video editing.
CPU may also have an impact. The slower CPU option is fine for general usage, but a faster CPU is needed for video editing and some games.
MacBook Pro 13 comes with 8GB and 16GB RAM options. Many are confused to chose RAM for MacBook. Here is a guide to choose 8GB vs. 16GB RAM MacBook Pro.
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