What are the two main functions of an operating system?
What is multiprogramming?
In Sec. 1.4, nine different types of operating systems are described. Give a list of possible applications for each of these systems (at least one for each of the operating systems types).
To use cache memory, main memory is divided into cache lines, typically 32 or 64 bytes long. An entire cache line is cached at once. What is the advantage of caching an entire line instead of a single byte or word at a time?
What is spooling? Do you think that advanced personal computers will have spooling as a standard feature in the future?
On early computers, every byte of data read or written was handled by the CPU (i.e., there was no DMA). What implications does this have for multiprogramming?
Why was timesharing not widespread on second-generation computers?
Instructions related to accessing I/O devices are typically privileged instructions, that is, they can be executed in kernel mode but not in user mode. Give a reason why these instructions are privileged.
One reason GUIs were initially slow to be adopted was the cost of the hardware needed to support them. How much video RAM is needed to support a character monochrome text screen? How much for a 24-bit color bitmap? What was the cost of this RAM at 1980 prices ? How much is it now?
There are several design goals in building an operating system, for example, resource utilization, timeliness, robustness, and so on. Give an example of two design goals that may contradict one another.
What is the difference between kernel and user mode? Explain how having two distinct modes aids in designing an operating system.
A 255-GB disk has 65,536 cylinders with 255 sectors per track and 512 bytes per sector. How many platters and heads does this disk have? Assuming an average cylinder seek time of 11 msec, average rotational delay of 7 msec. and reading rate of calculate the average time it will take to read 100 KB from one sector.
Consider a system that has two CPUs, each CPU having two threads (hyperthreading). Suppose three programs, P0, P1, and P2, are started with run times of 5, 10 and 20 msec, respectively. How long will it take to complete the execution of these programs? Assume that all three programs are 100% CPU bound, do not block during execution, and do not change CPUs once assigned.
List some differences between personal computer operating systems and mainframe operating systems.
A computer has a pipeline with four stages. Each stage takes the same time to do its work, namely, 1 nsec. How many instructions per second can this machine execute?
Consider a computer system that has cache memory, main memory (RAM) and disk, and an operating system that uses virtual memory. It takes 2 nsec to access a word from the cache, 10 nsec to access a word from the RAM, and 10 msec to access a word from the disk. If the cache hit rate is 95% and main memory hit rate (after a cache miss) is 99%, what is the average time to access a word?
When a user program makes a system call to read or write a disk file, it provides an indication of which file it wants, a pointer to the data buffer, and the count. Control is then transferred to the operating system, which calls the appropriate driver. Suppose that the driver starts the disk and terminates until an interrupt occurs. In the case of reading from the disk, obviously the caller will have to be blocked (because there are no data for it). What about the case of writing to the disk? Need the caller be blocked awaiting completion of the disk transfer?
What is the key difference between a trap and an interrupt?
Is there any reason why you might want to mount a file system on a nonempty directory? If so, what is it?
What is the purpose of a system call in an operating system?
Give one reason why mounting file systems is a better design option than prefixing path names with a drive name or number. Explain why file systems are almost always mounted on empty directories.
For each of the following system calls, give a condition that causes it to fail: open, close, and lseek.
What type of multiplexing (time, space, or both) can be used for sharing the following resources: CPU, memory, SSD/disk, network card, printer, keyboard, and display?
Can the
count = write(fd, buffer, nbytes);call return any value in count other than nbytes? If so, why?
A file whose file descriptor is fd contains the following sequence of bytes: 2, 7, 1, 8, 2, 8, 1, 8, 2, 8, 4. The following system calls are made:
lseek(fd, 3, SEEK SET);read(fd, &buffer, 4);
where the lseek call makes a seek to byte 3 of the file. What does buffer contain after the read has completed?
Suppose that a 10-MB file is stored on a disk on the same track (track 50) in consecutive sectors. The disk arm is currently situated over track number 100. How long will it take to retrieve this file from the disk? Assume that it takes about 1 msec to move the arm from one cylinder to the next and about 5 msec for the sector where the beginning of the file is stored to rotate under the head. Also, assume that reading occurs at a rate of
What is the essential difference between a block special file and a character special file?
In the example given in Fig. 1-17, the library procedure is called read and the system call itself is called read. Is it essential that both of these have the same name? If not, which one is more important?
The client-server model is popular in distributed systems. Can it also be used in a single-computer system?
To a programmer, a system call looks like any other call to a library procedure. Is it important that a programmer know which library procedures result in system calls? Under what circumstances and why?
Figure 1-23 shows that a number of UNIX system calls have no Win32 API equivalents. For each of the calls listed as having no Win32 equivalent, what are the consequences for a programmer of converting a UNIX program to run under Windows?
A portable operating system is one that can be ported from one system architecture to another without any modification. Explain why it is infeasible to build an operating system that is completely portable. Describe two high-level layers that you will have in designing an operating system that is highly portable.
Explain how separation of policy and mechanism aids in building microkernel-based operating systems.
Virtual machines have become very popular for a variety of reasons. Nevertheless, they have some downsides. Name one.
Here are some questions for practicing unit conversions:
How long is a microyear in seconds?
Micrometers are often called microns. How long is a gigamicron?
How many bytes are there in a 1-TB memory?
The mass of the earth is 6000 yottagrams. What is that in grams?
Write a shell that is similar to Fig. 1-19 but contains enough code that it actually works so you can test it. You might also add some features such as redirection of input and output, pipes, and background jobs.
If you have a personal UNIX-like system (Linux, MINIX 3, FreeBSD, etc.) available that you can safely crash and reboot, write a shell script that attempts to create an unlimited number of child processes and observe what happens. Before running the experiment, type sync to the shell to flush the file system buffers to disk to avoid ruining the file system. You can also do the experiment safely in a virtual machine. Note: Do not try this on a shared system without first getting permission from the system administrator. The consequences will be instantly obvious so you are likely to be caught and sanctions may follow.
Examine and try to interpret the contents of a UNIX-like or Windows directory with a tool like the UNIX od program. (Hint: How you do this will depend upon what the OS allows. One trick that may work is to create a directory on a USB stick with one operating system and then read the raw device data using a different operating system that allows such access.)