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? image shows a table with days: s, m, t, w, t, f, s; backup types: full, differential, incremental, differential, incremental, differential

Explanation:

Step1: Understand Backup Types

Full backup (Sunday) is the base. Differential backup includes all changes since the last full backup. Incremental includes changes since last backup (any type).

Step2: Analyze Wednesday's Backup

Wednesday is a Differential backup. Differential backups are based on the last full backup (Sunday). To restore Wednesday, after Sunday's full, we need the last differential before Wednesday? Wait, no: when restoring from a differential backup, the differential backup on Wednesday is based on Sunday. Wait, no—differential backup captures all changes from the last full. So if the computer crashes on Wednesday, the full backup (Sunday) and the last differential before or on Wednesday? Wait, the schedule: Sunday (Full), Monday (Differential), Tuesday (Incremental), Wednesday (Differential), Thursday (Incremental), Friday (Differential).

Differential backup: each differential includes all changes since the last full. So to restore Wednesday, we need the full (Sunday) and the latest differential before Wednesday? Wait, no—Wednesday's own backup is Differential. Wait, no: when a system crashes on Wednesday, to restore, we use the full backup (Sunday) and then the latest differential backup that includes changes up to Wednesday. Wait, the differential backups are on Monday, Wednesday, Friday. Wait, no: the table shows Sunday (Full), Monday (Differential), Tuesday (Incremental), Wednesday (Differential), Thursday (Incremental), Friday (Differential).

Wait, differential backup: each differential backup contains all changes since the last full backup (Sunday). So on Monday, differential has changes from Sunday to Monday. On Wednesday, differential has changes from Sunday to Wednesday. On Friday, changes from Sunday to Friday. Incremental on Tuesday: changes from Monday to Tuesday. Incremental on Thursday: changes from Wednesday to Thursday.

So if the computer crashes on Wednesday, we need to restore the full backup (Sunday) and then the differential backup from Wednesday? Wait, no—wait, the question is "apart from the full backup on Sunday, which day needs to be restored?" Wait, maybe I got it wrong. Wait, differential backup: when you do a differential backup, it's all changes since the last full. So to restore to Wednesday, after restoring Sunday's full, you need to restore the latest differential backup that is on or before Wednesday. The differential backups are Monday, Wednesday, Friday. So Wednesday's differential is the latest before (or on) Wednesday. Wait, but Wednesday is the day of the crash. Wait, maybe the key is: differential backups are cumulative from the last full. So to restore to Wednesday, you need Sunday's full and then Wednesday's differential? But the question is "apart from the full backup on Sunday, which day needs to be restored?" Wait, maybe I misread. Wait, the schedule: Sunday (Full), Monday (Differential), Tuesday (Incremental), Wednesday (Differential), Thursday (Incremental), Friday (Differential).

Wait, another approach: In differential backup strategy, each differential backup includes all changes since the last full. So to restore a system that crashed on Wednesday, you restore the full backup (Sunday) and then the latest differential backup prior to or on Wednesday. The differential backups are Monday, Wednesday, Friday. So Wednesday's differential is the latest one before (or on) Wednesday. Wait, but Wednesday is the crash day. So after Sunday's full, you need to restore Wednesday's differential? But the question is "apart from the full backup on Sunday, which day needs to be restored?" Wait, maybe the answer is Wednesday? No, wait, maybe I made a mistake. Wait, let's think again.

Wait, the backup types: Full (S), Differential (M), Incremental (T), Differential (W), Incremental (Th), Differential (F).

When restoring, for differential backup: you need the last full and then the last differential (because differential is cumulative from full). So if the crash is on Wednesday, the last differential before Wednesday is Monday? No, Wednesday's own backup is Differential. Wait, no—Wednesday's backup is done on Wednesday, so if the crash is on Wednesday, maybe the backup on Wednesday is not yet completed? Wait, the problem says "their computer crashes on Wednesday and they need to fully restore their data". So the backups are scheduled: Sunday (Full), Monday (Differential), Tuesday (Incremental), Wednesday (Differential) – so Wednesday's backup is a Differential. But when restoring, do we use the Wednesday's differential? Wait, no—because the crash is on Wednesday, maybe the Wednesday backup is corrupted or not available? Wait, the problem is asking "apart from the full backup on Sunday, which day needs to be restored?" So we need to find which backup (other than Sunday's full) is needed.

Wait, let's recall: In differential backup, each differential backup contains all changes since the last full. So to restore to a point in time, you need the full and then the latest differential. So if today is Wednesday, the latest differential is Wednesday's own backup? But if the computer crashes on Wednesday, maybe the Wednesday backup is not usable. Wait, no—the schedule is the backup schedule, so Wednesday's backup is a Differential, meaning that before Wednesday's crash, the administrator had done a Differential backup on Wednesday? Wait, maybe the key is that differential backups are cumulative from the last full, so to restore to Wednesday, you need the full (Sunday) and then the last differential before Wednesday, which is Monday? No, that can't be. Wait, no—Monday's differential is changes from Sunday to Monday. Wednesday's differential is changes from Sunday to Wednesday. So if you restore Sunday's full, then Wednesday's differential, you get all changes up to Wednesday. But if the crash is on Wednesday, maybe the Wednesday backup is not available, so you need the last differential before Wednesday, which is Monday? No, that doesn't make sense. Wait, maybe the answer is Monday? No, wait, let's look at the schedule again.

Wait, the table:

S: Full

M: Differential

T: Incremental

W: Differential

Th: Incremental

F: Differential

So the backup types: Differential backups are on M, W, F. Incremental on T, Th.

Now, when restoring from a differential backup strategy, the process is: restore the last full backup, then restore the last differential backup (because each differential includes all changes since the full). So if the crash is on Wednesday, the last differential backup before or on Wednesday is Wednesday's own backup. But if the crash happens during Wednesday, maybe the Wednesday backup is not complete, so we use the last differential before Wednesday, which is Monday? No, that's not right. Wait, maybe the question is simpler: the differential backup on Wednesday is based on Sunday, so to restore Wednesday, you need Sunday's full and Wednesday's differential. But the question is "apart from the full backup on Sunday, which day needs to be restored?" So the answer is Wednesday? Wait, but let's check again.

Wait, another angle: Incremental backups are based on the last backup (any type), so to restore from incremental, you need the full, then all incrementals and differentials in order. But differential is cumulative from full. So if we have a differential on Monday (changes from S to M), incremental on Tuesday (changes from M to T), differential on Wednesday (changes from S to W). Wait, no—differential is always from the last full, so Wednesday's differential includes S to W, which includes M to W. So if we restore S (full), then W (differential), we get all changes up to W. So apart from S, we need to restore W. But let's confirm.

Yes, because differential backup on Wednesday includes all changes since Sunday (full), so to restore Wednesday's data, after Sunday's full, we need to restore Wednesday's differential backup. So the day is Wednesday. Wait, but the schedule shows Wednesday as Differential. So the answer should be Wednesday.

Answer:

Wednesday