MacBook Pro and MacBook Air models (including all the “Retina” screen models) lost the ability to have the memory upgraded (you are stuck with the RAM that the motherboard was made with). At the same time, Apple discontinued 2.5 inch SATA hard drives in these models and changed to proprietary Apple SSD designs. Many of these models can have the internal SSD upgraded, but the SSD has to be carefully matched to the model and year of Mac.
What does “proprietary” mean? Proprietary means a physical or electronic design which doesn’t conform to industry standards. So industry standard parts like M.2 SSDs cannot be used in many Apple models Late 2012 and newer; only Apple parts or specialty replacement parts engineered to conform to Apple’s specifications can be used. Confusingly, Apple has used at least 6 different proprietary SSD designs in the past 8 years, so matching part to machine year and model is especially important.
iMac machines continued to use spinning hard drives, but added a SSD slot on some models for a “Fusion” drive, which is a combination of hard drive and a small SSD for caching reads and writes for higher speed. The Fusion drive set can be broken to use the SSD and hard drive separately. RAM is easily upgradeable in the 27 inch iMacs to date, with a trap door on the back of the machine. However the 21 inch models put the RAM internally. The Retina screen iMacs from Late 2012 onward make it difficult to access the internals for upgrading drives (and RAM on the 21 inch) as the screen is glued to the machine, and has to be carefully unglued to access the motherboard and drives. CanadaRAM sells OWC kits with the tools and adhesive for reinstalling the screen. This service should only be attempted by technician or an owner who is experienced with disassembly.
The iMac Pro model uses SSD drives only, and there are currently no aftermarket options but it is upgradeable in RAM (using server-class ECC DIMM memory) with the same caveats about installation behind the Retina screen.
The 2013 Mac Pro (cylindrical, black model) deleted the ability to have internal hard drives, and went with a proprietary SSD format. It still has four RAM DIMM sockets for upgrading. The 2019 Mac Pro also has 2 SSD sockets, and eight RAM DIMM sockets.
Mac Mini machines were produced in several variants. 2.5 inch SATA drives continued to be used up to the Late 2014 model. RAM upgrades are not possible on the Late 2014, but upgradeable RAM returned in the Mini 2018 model.
MacBook machines newer than the 2010 model have no internal upgrade options at all.
Canadaram carries OWC and Transcend have SSD drives that are designed for specific Macintosh models.
This is a bit complex because there are many models of Macs. This list is ordered by the the type of Mac and then Macintosh ID number which roughly corresponds to the model date. Some models have both SATA drive connectors and SSD connectors, some have only one or the other.