Operating systems provide a mechanism for selectively calling certain functions in the kernel. These select functions are called kernel calls or system calls, and act as gateways into the kernel. These gateways are carefully designed to provide safe functionality. They carefully check their parameters and understand how to move data from a user process into the kernel and back again. We will discuss this topic in more detail in the Memory Management section of the course.
The path in and out of the kernel
The only way to enter the operating kernel is to generate a processor interrupt. Note the emphasis on the word "only". These interrupts come from several sources:
I/O devices: When a device, such as a disk or network interface, completes its current operation, it notifies the operating system by generating a processor interrupt.
Clocks and timers: Processors have timers that can be periodic (interrupting on a fixed interval) or count-down (set to complete at some specific time in the future). Periodic timers are often used to trigger scheduling decisions. For either of these types of timers, an interrupt is generated to get the operating system's attention.
Exceptions: When an instruction performs an invalid operation, such as divide-by-zero, invalid memory address, or floating point overflow, the processor can generate an interrupt.
Software Interrupts (Traps): Processors provide one or more instructions that will cause the processor to generate an interrupt. These instructions often have a small integer parameter. Trap instructions are most often used to implement system calls and to be inserted into a process by a debugger to stop the process at a breakpoint.
The flow of control is as follows (and illustrated below):
The general path goes from the executing user process to the interrupt handler. This step is like a forced function call, where the current PC and processor status are saved on a stack.
The interrupt handler decides what type of interrupt was generated and calls the appropriate kernel function to handle the interrupt.
The general run-time state of the process is saved (as on a context switch).
The kernel performs the appropriate operation for the system call. This step is the "real" functionality; all the steps before and after this one are mechanisms to get here from the user call and back again.
if the operation that was performed was trivial and fast, then the kernel returns immediately to the interrupted process. Otherwise, sometime later (it might be much later), after the operation is complete, the kernel executes its short-term scheduler (dispatcher) to pick the next process to run.
Note that one side effect of an interrupt might be to terminate the currently running process. In this case, of course, the current process will never be chosen to run next!
The state for the selected process is loaded into the registers and control is transferred to the process using some type of "return from interrupt" instruction.
The system call path
One of the most important uses of interrupts, and one of the least obvious when you first study about operating systems, is the system call. In your program, you might request a UNIX system to read some data from a file with a call that looks like:
Questions & Answers
differentiate between demand and supply
giving examples
In economics, a perfect market refers to a theoretical construct where all participants have perfect information, goods are homogenous, there are no barriers to entry or exit, and prices are determined solely by supply and demand. It's an idealized model used for analysis,
When MP₁ becomes negative, TP start to decline.
Extuples Suppose that the short-run production function of certain cut-flower firm is given by: Q=4KL-0.6K2 - 0.112 •
Where is quantity of cut flower produced, I is labour input and K is fixed capital input (K-5). Determine the average product of lab
Kelo
Extuples Suppose that the short-run production function of certain cut-flower firm is given by: Q=4KL-0.6K2 - 0.112 •
Where is quantity of cut flower produced, I is labour input and K is fixed capital input (K-5). Determine the average product of labour (APL) and marginal product of labour (MPL)
Quantity demanded refers to the specific amount of a good or service that consumers are willing and able to purchase at a give price and within a specific time period. Demand, on the other hand, is a broader concept that encompasses the entire relationship between price and quantity demanded
Ezea
ok
Shukri
how do you save a country economic situation when it's falling apart
Economic growth as an increase in the production and consumption of goods and services within an economy.but
Economic development as a broader concept that encompasses not only economic growth but also social & human well being.
Shukri
production function means
Jabir
What do you think is more important to focus on when considering inequality ?
sir...I just want to ask one question... Define the term contract curve? if you are free please help me to find this answer 🙏
Asui
it is a curve that we get after connecting the pareto optimal combinations of two consumers after their mutually beneficial trade offs
Awais
thank you so much 👍 sir
Asui
In economics, the contract curve refers to the set of points in an Edgeworth box diagram where both parties involved in a trade cannot be made better off without making one of them worse off. It represents the Pareto efficient allocations of goods between two individuals or entities, where neither p
Cornelius
In economics, the contract curve refers to the set of points in an Edgeworth box diagram where both parties involved in a trade cannot be made better off without making one of them worse off. It represents the Pareto efficient allocations of goods between two individuals or entities,
Cornelius
Suppose a consumer consuming two commodities X and Y has
The following utility function u=X0.4 Y0.6. If the price of the X and Y are 2 and 3 respectively and income Constraint is birr 50.
A,Calculate quantities of x and y which maximize utility.
B,Calculate value of Lagrange multiplier.
C,Calculate quantities of X and Y consumed with a given price.
D,alculate optimum level of output .
the market for lemon has 10 potential consumers, each having an individual demand curve p=101-10Qi, where p is price in dollar's per cup and Qi is the number of cups demanded per week by the i th consumer.Find the market demand curve using algebra. Draw an individual demand curve and the market dema
suppose the production function is given by ( L, K)=L¼K¾.assuming capital is fixed find APL and MPL. consider the following short run production function:Q=6L²-0.4L³ a) find the value of L that maximizes output b)find the value of L that maximizes marginal product
