Historically, McKinsey only had two tracks in its core consulting work (what we call "client service"): the Generalist track, and the "Non-Electable" Practice Expert track. In addition to those was the Research track, which performs some (but not only) client service, the "Knowledge" Expert track. Recently, the Practice Expert track has added an "Electable" branch
1. Generalist track: (Senior) Business Analyst, (Junior/Senior) Associate (=MBA), Engagement Manager, Associate Partner, Partner, Senior Partner - this is the classical track, as such you belong (and are hired/reviewed) by an Office (e.g. New York Office). There a few exceptions to this rule, where for historical reasons Practices were allowed to hire and review: the biggest of which are the Operations Practice and the Business Technology Office (BTO)
2a. "Non-Electable" Practice Expert track: (Junior/Senior) Analyst, Specialist (=MBA), Expert, Senior Expert, Master Expert
2b. "Electable" Practice Expert track: (Junior/Senior) Analyst, Specialist (=MBA), Expert, Expert Associate Partner, Expert Partner
The difference between those two is that "Electable" Experts get Additional Award (= Firm profit share) in exchange for more demand requirements. Compared to track 1, (i) you get more time to evolve between roles (and hence lower raises since the scale is roughly similar), (ii) you technically cannot become a Senior Partner (although it has happened), (iii) you belong to a Practice (either horizontal e.g. Marketing or more rarely vertical e.g. Automotive), which is in charge of your reviews and hence will ask you to balance client work with practice contributions. In practice, Expert consultants serve a larger number of clients on a narrower topic range (which they have to consistently develop).
Interviews for 1) and 2) are technically the same but respectively performed by Offices and Practices. In practice it is quite easy and frequent to switch between those tracks (1 and 2, and 2a and 2b) while at the Firm.
3. Research track: (Junior/Senior) Research Analyst, Knowledge Specialist (=MBA), Knowledge Expert, Senior Knowledge Expert, Director of Knowledge. Knowledge staff primarily supports consulting teams remotely, although they do sometimes get staffed. They have lower pay for similar roles, all belong to Practices (horizontal or vertical) and the interview process is different altogether. Consultants sometimes switch to the Research track, but the reverse is more rare
Recently, McKinsey has introduced new roles with the McKinsey Solutions umbrella. There are too many to list out but as you mention Implementation has a pretty similar scale as the above roles:
4. Implementation track: (Junior) Implementation Coach, Senior Implementation Coach (=MBA), Implementation Vice President, Implementation Senior Vice President, (next would be a Partner equivalent, but I have never met one). In this track, you work on longer studies that require ongoing implementation commitments. Pay is a bit lower than 1&2 but higher than 3.
To your specific question about the Operations practice, this is where it gets a bit tricky. You could be focused on Operations work and be any of those roles:
- Generalist consultant (track 1) who just happens to do a lot of Ops work although he was hired, belongs, and is reviewed by an Office
- Operations Generalist (track 1) - belongs to Ops practice but can go all the way to Senior Partner on classical track
- Operations Practice Expert (track 2) - belongs to Ops practice but goes through track 2 and will have to fulfill more practice commitments than 1
- Operations Knowledge Expert (track 3)
- Implementation consultant (track 4), which are most often Ops-focused
BTO follows the same logic as Ops.