A simultaneous capacity slot is a specific date, shift and start time at which every machine in a parallel group can begin the same operation together. Finding one is the precondition for scheduling any parallel work, because parallelism only means anything if the machines actually run concurrently. A candidate moment is not a slot until it passes four separate checks, and failing any one of them rejects the whole moment rather than the individual machine that failed. EDGEBIC by User Solutions searches forward day by day for the first moment that satisfies every member of the group.
How it works
The search begins by finding shifts the group's machines have in common, because a common start time is impossible without a shared window. This matching is by shift identity rather than by the hours a shift contains, which is worth stating explicitly: two shifts both running eight in the morning to four in the afternoon, saved as two separate records, are not a common shift. They look identical on a report and are unrelated to the scheduler.
Within each common shift, a candidate start time is proposed and put through four gates.
Individual capacity. Every machine in the group must have a real capacity record for that date and shift, and must offer a usable amount of free time from the proposed start onward. A machine that is fully booked, closed for a holiday, or simply not associated with that shift fails here.
Simultaneous start. The proposed moment must fall inside each machine's shift window, and no machine may already have an allocation running across that exact instant. This is stricter than merely having hours free somewhere in the shift: the group needs to start together at one specific time, so a machine free from midday is no use for a nine o'clock start.
Instance conflicts. Each machine must have enough physical units available for its share, and no unit may be double-booked across the group. A group cannot satisfy itself by counting the same machine twice.
Continuous capacity. The capacity must run uninterrupted from the start through to the projected finish. Free hours split around an existing booking do not qualify, because the operation cannot pause mid-way and resume around somebody else's job.
If all four pass, the moment is a slot and the group is scheduled into it. If any one fails, the whole moment is discarded and the search advances to the next candidate. This is the all-or-nothing principle: either every machine in the group works together, or none of them start until they can.
A concrete example
An operation runs on three drill heads working in parallel. All three share the same day shift record, and the operation is ready Monday morning.
Monday is tested. Drill 1 and Drill 3 are free from 08:00. Drill 2 is booked until 14:00 on another job. The first gate passes for all three, since all three do have some free capacity that day. The second gate fails: at 08:00, Drill 2 is running something else, so the group cannot start together. The moment is rejected.
A 14:00 start is tested. All three can start then, and all three are inside the shift window. But the operation needs four hours, and the shift ends at 16:00. The fourth gate fails on continuity: there are only two uninterrupted hours before the shift closes. Rejected.
Tuesday 08:00 is tested. All three are free, all three are in the window, each has its own physical unit, and four uninterrupted hours are available on every one. All four gates pass. The group is scheduled Tuesday 08:00 to 12:00 on all three drills.
Note what happened to Drill 1 and Drill 3. Both were free all Monday and both stayed empty as far as this operation was concerned, because a group waits for its slowest member. A planner reading only Monday's utilization sees two idle drills and an operation that did not run, and the explanation is entirely in the third machine's diary.
How EDGEBIC uses it
Slot finding runs before any parallel allocation, and it is where most parallel scheduling questions are actually answered. The four gates are described in how EDGEBIC validates simultaneous capacity, and the shared window they depend on is covered in what is a common shift requirement in parallel scheduling, which is also where the duplicate-shift trap is laid out.
The slot serves both parallel models, though for different reasons. Independent parallel machines each consume their own capacity and genuinely need every gate, which is described in what is independent parallel processing and worked through in how independent parallel splits a job across machines. Dependent parallel machines mirror the primary's window rather than booking independently, described in what is dependent parallel processing.
When no slot can be found within the search horizon the run reports a failure rather than inventing a partial arrangement, which is deliberate and is the same discipline described in what is atomic rollback in production scheduling. For the wider picture see EDGEBIC parallel work centers explained.
The takeaway
A simultaneous capacity slot is the intersection of several machines' availability, and an intersection is only ever as generous as its narrowest member. That single fact explains almost every surprise parallel scheduling produces: a group that slides days later than any one machine needed, partners sitting visibly idle, and the whole arrangement waiting on one busy drill. When a group refuses to schedule at all rather than merely scheduling late, the first thing to check is not capacity but shift records, because machines that appear to work identical hours through two separate shift entries share no window at all. For the wider vocabulary see the manufacturing glossary, and for the product itself see EDGEBIC.
It is a specific date, shift and start time at which every machine in a parallel group can begin the same operation together. Finding one is a precondition for scheduling parallel work, because the whole point of running machines in parallel is that they run at the same time. A candidate moment becomes a slot only after passing four separate checks covering individual capacity, an exact common start, physical machine availability, and uninterrupted capacity through to the projected finish.
Because a parallel group is one operation split across several machines rather than several independent operations that happen to be related. Starting two of three machines does not produce two thirds of the work, it produces a partial arrangement nobody asked for and that nothing downstream expects. If any machine in the group cannot make a moment work, the whole moment is rejected and the search moves on until it finds one that suits every member.
Because the group waits for the first moment that suits all of its members, and the constraint is the intersection rather than any one machine. A machine that is fully booked Monday and Tuesday sets the earliest possible start for the whole group even if its partners are free from Monday morning. This is a common and correct outcome, and it is also why a parallel group is worth reviewing whenever one of its machines takes on unrelated work.
Almost certainly that they use two separate shift records rather than the same one. The common shift check matches shifts by identity, not by the hours they happen to contain, so a day shift saved twice as two records looks like two different shifts even though both run eight to four. The fix is to associate every member of the group with the same shift record and delete or stop using the duplicate. This is the single most frequent cause of a parallel group that never schedules.
No. The whole group slips, because the group needs a moment that works for every member and that moment cannot arrive until the downed machine is back. Its partners stay idle for the group's purposes during those two days, though they remain free for other jobs. If the work genuinely does not need to be synchronized, that is a signal the routing should model it as independent alternates rather than as a parallel group.
Expert Q&A: Deep Dive
Q: Two of my machines run identical hours but the group never finds a slot. What is wrong?
A: Almost certainly that they use two separate shift records rather than the same one. The common shift check matches shifts by identity, not by the hours they happen to contain, so a day shift saved twice as two records looks like two different shifts even though both run eight to four. The fix is to associate every member of the group with the same shift record and delete or stop using the duplicate. This is the single most frequent cause of a parallel group that never schedules.
Q: One machine in my group went down for two days. Should I expect only that machine's work to slip?
A: No. The whole group slips, because the group needs a moment that works for every member and that moment cannot arrive until the downed machine is back. Its partners stay idle for the group's purposes during those two days, though they remain free for other jobs. If the work genuinely does not need to be synchronized, that is a signal the routing should model it as independent alternates rather than as a parallel group.
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