From Schaum's Os (6)

[naveednaseer]

Can anybody explain me question no. 6.24 in Chapter 6 of Schaum's Outlines Operating System in detail I cannot get it right. Thanks in advance.

[rafi_dery]

Can you please repeat the question in the forum? (I do not have the book...). Thanks.

[wood]

6.24 On a capability-based system, each file is associated with a unique 16-bit number. For each file, each user may have the read or write capability. How many bytes are needed to store each user's access data?

Answer:

Each file has a unique 16-bit number. That means that you can identify any given file using a 16-bit number (i.e., 0x0A45 or 0x0FEA). That also means that there are 2^16 files in this hypothetical OS, making it 65,536 possible files.

Keep in mind that you need 2 bits to store the user's access data per file. For example:

00 - neither read nor write
01 - read but no write
10 - write but no read
11 - read and write

So for all possible files, you need 2 bits x 2^16 files = 131,072 bits per user to store the access data. That makes 16,384 bytes.

[SalmanKhana]

hey is calculator allowed in the exam ?

[wood]

Nope... I don't think so.

[naveednaseer]

Thanks wood for your explanation it was just great!!!!!!!

[wood]

You're welcome...!