1

What is an "Operating System"? (20 pts)

The answer can be found among the solutions of previous mid term exams.

2

What is an “Operating System Kernel”? (20 pts)

The answer can be found among the solutions of previous mid term exams.

3

What is (are) the difference(s) between “device drivers” and “device controllers”? (10 pts)

The answer can be found among the solutions of previous mid term exams.

4

Explain in detail how “Public Key Cryptography” (for example: PGP) works. (20 pts)

The Public Key Cryptography works by encrypting a plain text using a key which is publicly available for everyone but decrypted by a key known only by the recipient. The technique is based on two pairs of keys generated by both the sender and the recipient (P1-P2) and (Q1-Q2). Suppose person A wants to send a crypted message to person B. B sends to A his/her public key (P1). (there is no risk in doing this because P1 is a public key and can be disclosed to anyone). Knowing B's P1 public key; A encrypts the message with this key ( P1(msg) ) and sends it over to B. Now B must use his/her private key (P2) to decrypt this message. Please note that since P2, the private key is not known by any other person. Public and private keys are based on very large prime numbers and it is practically impossible to guess what P2 (private key) is knowing P1 (the public key) and having the crypted text (cypher text) in your hands.

5

Compare “multi-tasking” and “multi-user” operating systems. Give examples. (20 pts)

An example for a multitasking opsys is MS-Windows family, whereas an example of a multi-user opsys is UNIX.

6

Explain what “Real Time Operating Systems” are. (10 pts)

Software running on computers which control industrial processes are usually required to do certain tasks at certain exact times. These tasks have to be done at precise points in time and the operating system should allocate the necessary resource at the correct instant to the correct task. You can consider a computer controllng a nuclear power plant where the process should be under very precise control. Certain measurements must be taken at precise intervals and the software must take precise actions depending on these measurements.

7

Bonus Question - What does “network appliance” (or “Internet appliance”) mean? (10 pts)

Network Appliances are simple computers and/or electronic devices which can only perform reasonable tasks when they are connected to a network and use the resources on a server. Network Appliances usually do not have local disk storage capability. They are equipped with a reasonable CPU and sufficient RAM. Since they do not have local disks they must download their application software and possibly their operating system from the servers. Network PC, Thin-Client are other names used for network appliances.

8

Bonus Question – What is a “port” in TCP/IP terminology? (10 pts)

"TCP/IP Port" is a numerical code used to express the kind of service requested by one network client from another. The "port" identifier within the network message (packet) is examined by the recipient client and passed to the appropriate software service running on the recipient to be processed. The telnet service, for instance, is represented by port 23. That is to say, when a client needs to telnet to a remote host, it sends a TCP/IP request with the service code 23. The receiving end computer, recognizing this packet requesting a telnet service, passes this message to the software handling telnet services and so forth.