If you have ever wondered why the roster in your establishment register is tied to sanctioned posts rather than to the vacancies of a year, the answer is a Constitution Bench judgment of February 1995 and the Office Memorandum that implemented it two years later. Understanding why the change was made is the fastest way to get the replacement principle right, because almost every operating error in a post-based roster is a leftover habit from the system it replaced.
What the vacancy-based roster did
Before 2 July 1997, reservation was applied to the vacancies filled in a recruitment year. The roster ran as a running account: if the appointments made in one year stopped at point 6, the next year's recruitment resumed at point 7, and the cycle continued indefinitely.
Three rosters were in use — a 200-point roster, a 40-point roster, and a third for Group C and D posts recruited on a regional basis. The essential feature they shared was that they measured reservation against the flow of recruitment rather than the stock of posts.
Why that failed
A running account has no natural stopping point. Once a cadre already held the prescribed percentage of a reserved category, the roster went on generating fresh reserved points at every cycle, so representation could drift past the prescribed percentage without limit. In a cadre with low turnover the opposite happened: reserved points might never be reached at all, because too few vacancies arose to advance the roster far enough.
Neither outcome matched what Article 16(4) actually requires, which is that a backward class not adequately represented in the services should be brought up to adequate representation — a statement about the composition of the cadre, not about the sequence of appointments.
R.K. Sabharwal v. State of Punjab
Decided on 10 February 1995, reported at (1995) 2 SCC 745, by a Constitution Bench of five judges — Kuldip Singh, Mohan, Mukherjee, Hansaria and Majmudar JJ.
The Court's reasoning is short and worth reading in the original words: the cadre-strength is always measured by the number of posts comprising the cadre. Right to be considered for appointment can only be claimed in respect of a post in a cadre. As a consequence the percentage of reservation has to be worked out in relation to the number of posts which form the cadre-strength. And then the sentence that decided the matter: the concept of 'vacancy' has no relevance in operating the percentage of reservation.
The Court also settled what happens once the roster has run its course. The roster operates only until the cadre strength is filled. Once the number of posts held by a reserved category reaches the prescribed percentage of the cadre, the roster is exhausted. Thereafter a vacancy arising at any roster point is filled by a candidate of the category to which that post belonged in the roster. That is the replacement principle.
The 1997 Office Memorandum
The Department of Personnel and Training gave effect to the judgment by Office Memorandum No. 36012/2/96-Estt.(Res.) dated 2 July 1997, which replaced the existing vacancy-based rosters with post-based rosters and set out an Explanatory Note on how they are to be prepared and operated.
The Explanatory Note states the change in one line: the roster is to be operated on the principle of replacement and not as a 'running account' as hitherto. In other words, the points at which reservation for different categories applies are fixed as per the roster and vacancies caused by retirement, etc., of persons occupying those points shall be filled by appointment of persons of the respective categories.
The same Office Memorandum directs that direct recruitment and promotion be maintained on separate rosters, for the reason set out in Part 1: reservation for the Other Backward Classes does not apply in promotion, so the category sets differ.
What changed in practice
The post carries the category, permanently. Point 7 is an SC point. When the SC officer holding it retires, resigns, dies or is promoted out of the cadre, the post falls vacant as an SC post and is filled by an SC candidate. The category does not follow the person and does not move with the year.
The roster is a picture of the cadre now, not a history of recruitment. It is tied to the sanctioned strength. If posts are created or abolished, the roster is recast to the new strength — you do not append fresh points to the old roster.
The percentage self-limits and self-corrects. Because entitlement is computed against the number of posts, a category cannot drift past its percentage, and a cadre with low turnover still shows the correct entitlement even if the vacancies to fill it have not yet arisen.
The habits that cause errors
Most operating mistakes in a post-based roster are the reflexes of the older system. Three recur.
The first is treating a reserved vacancy as belonging to the year rather than to the post — asking "how many SC vacancies do we have this year" instead of "which points are vacant, and what are they earmarked as". The second is carrying the roster forward from where recruitment last stopped, which is precisely the running-account behaviour the change abolished. The third is failing to recast when the sanctioned strength changes, so the roster silently describes a cadre that no longer exists.
If you want to test whether the principle has landed, the second exercise in the Reservation Roster Trainer is built entirely around it.
One important exception
The DoPT model roster is not universal. Following the Supreme Court's order of 27 November 2024 in SLP (Civil) No. 10017 of 2022, Indian Railways applies the roster point table in the Indian Railway Establishment Manual, given effect by Railway Board RBE No. 17/2025 dated 6 March 2025. The two tables differ from the first points onward. Establishment officers in Railways, and in departments that had migrated to the DoPT model, need to be clear about which one governs them.
Frequently Asked Questions (FAQ)
Q1. What is the replacement principle in one sentence?
A post keeps the category earmarked against its roster point, so a vacancy arising at that point is filled by a candidate of that category, whatever the reason the post fell vacant.
Q2. An SC officer is promoted out of the cadre. Does the post stay SC?
Yes. Promotion out of the cadre is treated in the same way as retirement or resignation — the officer leaves, the post falls vacant, and the post retains its earmarked category. What happens to that officer in the higher grade is governed by the higher grade's own roster.
Q3. The sanctioned strength of our cadre has increased. What do we do with the roster?
Recast it to the new strength. The post-based roster describes the cadre as it currently stands, so entitlement for each category is recomputed against the new number of posts. Adding the new posts as extra points at the end of the existing roster produces the wrong distribution.
Q4. Does the vacancy-based roster survive anywhere?
For SC, ST, OBC and EWS in Central Government establishments, no — those are post-based since 1997. But the horizontal reservations run differently: the rosters for persons with benchmark disabilities and for ex-servicemen are vacancy-based and operate as a running account. They sit alongside the post-based roster as separate registers with a different logic, which is covered in Part 9.
Related Reading
Next: the percentages, and why they differ by mode of recruitment. Part 5 then covers how the roster points are actually derived.