Festplatte und Cloudspeicher enthalten dieselbe Sicherungskopie.

Because the subject is plural.

The subject is Festplatte und Cloudspeicher = hard drive and cloud storage. Two nouns joined by und usually make a plural subject, so the verb must also be plural:

• die Festplatte enthält = the hard drive contains
• der Cloudspeicher enthält = the cloud storage contains
• Festplatte und Cloudspeicher enthalten = the hard drive and cloud storage contain

So enthalten is the correct 3rd person plural form.

German often leaves out articles in general statements, headings, labels, or when the sentence is talking about things in a broad, non-specific way.

So:

• Die Festplatte und der Cloudspeicher enthalten ... would also be possible if you mean specific items
• Festplatte und Cloudspeicher enthalten ... sounds more general, like a neutral statement about those two storage locations

English also sometimes does something similar in short labels or technical writing, though German allows it a bit more naturally in some contexts.

Here it is singular.

The noun itself is singular: der Cloudspeicher.
Its plural can also be die Cloudspeicher.

In this sentence, Cloudspeicher is singular, but the whole subject becomes plural because it is joined with Festplatte by und:

• Festplatte = singular
• Cloudspeicher = singular
• Festplatte und Cloudspeicher = plural together

That is why the verb is enthalten.

Dieselbe means the very same or one and the same.

It is stronger than just saying two things are similar. The sentence means both storage locations contain one identical backup copy, not merely similar copies.

German often distinguishes:

• dieselbe = the same one
• die gleiche = an equivalent one / one just like it

In everyday speech, many people use them less strictly, but the formal distinction is:

• dieselbe Datei = literally the exact same file
• die gleiche Datei = a file of the same kind, sometimes a separate copy depending on context

So dieselbe Sicherungskopie emphasizes identity.

Because Sicherungskopie is:

1. feminine: die Sicherungskopie
2. singular
3. in the accusative case here, because it is the direct object of enthalten

For a feminine singular noun in nominative or accusative, the form is dieselbe.

Compare:

• derselbe Speicher = masculine singular
• dieselbe Sicherungskopie = feminine singular
• dasselbe Backup = neuter singular
• dieselben Dateien = plural

So the ending matches the gender and number of Sicherungskopie.

It is in the accusative case.

The verb enthalten takes a direct object: what is being contained?

• Festplatte und Cloudspeicher = subject
• enthalten = verb
• dieselbe Sicherungskopie = direct object

So the question is:

• What do the hard drive and cloud storage contain?
  Dieselbe Sicherungskopie.

That makes it accusative.

Because Sicherungskopie is feminine, the accusative singular form looks the same as the nominative singular form:

• nominative: dieselbe Sicherungskopie
• accusative: dieselbe Sicherungskopie

It is feminine: die Sicherungskopie.

A useful clue is the ending -kopie, which is almost always feminine in German:

• die Kopie
• die Fotokopie
• die Sicherungskopie

Also, the first part of a compound noun does not decide the gender. The last part usually does. Since the base noun is Kopie, the compound Sicherungskopie is also feminine.

German very often combines nouns into one long noun.

Here you have:

• Festplatte = fest

  • Platte
    Literally something like fixed plate, but the actual meaning is hard drive or hard disk

• Cloudspeicher = Cloud

  • Speicher
    Literally cloud storage

• Sicherungskopie = Sicherung

  • Kopie
    Literally backup copy

In German, these compounds are written as one word. The final part is the main noun, and it determines the gender and plural behavior.

You may hear that in everyday speech, but dieselbe is better if you want to be precise.

Traditional distinction:

• dieselbe Sicherungskopie = literally the exact same backup copy
• die gleiche Sicherungskopie = a backup copy of the same kind, or one that is identical, but not necessarily the exact same one

In real-life German, many speakers use die gleiche where stricter grammar would prefer dieselbe. Still, for learners, it is good to understand that dieselbe is the more exact choice here.

Yes, but the verb still has to stay in the second position in a normal main clause.

The neutral order is:

• Festplatte und Cloudspeicher enthalten dieselbe Sicherungskopie.

You could also front the object for emphasis:

• Dieselbe Sicherungskopie enthalten Festplatte und Cloudspeicher.

That is grammatically possible, but it sounds more marked or stylistically emphasized. The original sentence is the most natural neutral version.

Because in German, all nouns are capitalized.

So in this sentence:

• Festplatte
• Cloudspeicher
• Sicherungskopie

are capitalized simply because they are nouns.

This is a standard rule of German spelling and is one of the big visual differences from English.