Question

refer to the image. an administrator has constructed a backup schedule for their machine. their computer crashes on wednesday and they need to fully restore their data. apart from the full backup on sunday, which day needs to be restored? table with days: s, m, t, w, t, f, s; backup types: full, differential, incremental, differential, incremental, differential, (last s empty)

Explanation:

Step1: Understand Backup Types

Differential backup includes all changes since the last full backup. Incremental includes changes since last backup (any type). For restoration on Wednesday, after Sunday's full, we need the latest differential before Wednesday that includes all changes up to Wednesday.

Step2: Analyze the Schedule

Sunday: Full. Monday: Differential (captures changes since Sunday). Tuesday: Incremental (changes since Monday). Wednesday: Differential (captures changes since Sunday, including Monday, Tuesday, and Wednesday). Wait, no—wait, when restoring on Wednesday, the differential backup on Wednesday? Wait, no, the schedule: Sunday (Full), Monday (Differential), Tuesday (Incremental), Wednesday (Differential). Wait, differential backup on Wednesday: it includes all changes since Sunday (full). So to restore on Wednesday, after Sunday's full, we need the latest differential before or on Wednesday. Wait, the crash is on Wednesday. So the backups are: Sunday (Full), Monday (Differential), Tuesday (Incremental), Wednesday (Differential). Wait, no—wait, differential backup on Monday: changes since Sunday. Tuesday: incremental (changes since Monday). Wednesday: differential (changes since Sunday). So when restoring on Wednesday, the full backup (Sunday) plus the latest differential backup that includes all changes up to Wednesday. The latest differential before Wednesday is Monday? No, Wednesday's differential is on Wednesday. Wait, the computer crashes on Wednesday. So the backups available are Sunday (Full), Monday (Differential), Tuesday (Incremental), Wednesday (Differential) (but if it crashes on Wednesday, maybe the Wednesday backup isn't completed? Wait, the problem says "apart from the full backup on Sunday, which day needs to be restored". Wait, maybe the differential backup on Monday? No, wait, differential backup: a differential backup includes all changes since the last full backup. So Monday's differential: changes from Sunday to Monday. Tuesday's incremental: changes from Monday to Tuesday. Wednesday's differential: changes from Sunday to Wednesday. So if we restore Sunday's full, then the latest differential backup that includes all changes up to Wednesday is Wednesday's? But the problem says "apart from the full backup on Sunday, which day needs to be restored". Wait, maybe I misread. Wait the schedule: S (Full), M (Differential), T (Incremental), W (Differential), T (Incremental), F (Differential), S. So when the computer crashes on Wednesday, to restore, we need the full (Sunday) and the latest differential backup that includes all changes up to Wednesday. The differential backups are on Monday, Wednesday, Friday. The latest differential before or on Wednesday is Wednesday's? But if it crashes on Wednesday, maybe the Wednesday backup is being done or not. Wait, maybe the key is that differential backup on Wednesday includes all changes since Sunday, so after restoring Sunday's full, we need to restore Wednesday's differential? But the problem says "apart from the full backup on Sunday, which day needs to be restored". Wait, maybe I made a mistake. Wait, let's recall: in differential backup, each differential backup includes all changes since the last full. So Sunday (Full). Monday (Differential): changes from Sunday to Monday. Tuesday (Incremental): changes from Monday to Tuesday. Wednesday (Differential): changes from Sunday to Wednesday (so it includes Monday, Tuesday, Wednesday changes). So to restore on Wednesday, we need Sunday's full and Wednesday's differential? But the problem says "apart from the full backup on Sunday, which day needs to be restored". Wait, maybe the answer is Wednesday? But let's check again. Wait, the schedule: S (Full), M (Differential), T (Incremental), W (Differential), T (Incremental), F (Differential), S. So when the crash is on Wednesday, the backups available are Sunday (Full), Monday (Differential), Tuesday (Incremental), Wednesday (Differential) (assuming the Wednesday backup is completed before the crash? Or maybe not. Wait, maybe the differential backup on Monday is not enough, because Tuesday's incremental is on top of Monday's differential. Wait, no—restoration with differential and incremental: if you use differential, you restore full + latest differential. If you use incremental, you restore full + all incrementals since last full. But in this case, the backups are: Full (S), Differential (M), Incremental (T), Differential (W). So the differential on W includes all changes from S to W (including M, T, W). So to restore, you need S (Full) and W (Differential). But the problem says "apart from the full backup on Sunday, which day needs to be restored". So the day is Wednesday? Wait, but let's check the schedule again. Wait, the user's image: S (Full), M (Differential), T (Incremental), W (Differential), T (Incremental), F (Differential), S. So when the computer crashes on Wednesday, the latest differential backup before or on Wednesday is Wednesday's. So apart from Sunday's full, we need to restore Wednesday's differential. Wait, but maybe I'm wrong. Wait, another approach: differential backup on Monday: includes changes from Sunday to Monday. Then Tuesday's incremental: changes from Monday to Tuesday. Then Wednesday's differential: includes changes from Sunday to Wednesday (so it's a new differential, including all changes since Sunday, so it includes Monday, Tuesday, Wednesday). So when restoring, if we use differential, we can restore Sunday's full and Wednesday's differential, which will include all changes up to Wednesday. So the day to restore apart from Sunday is Wednesday.

Answer:

Wednesday (W)