Things I Learned

The abstraction provided by the OS of a running program is something we call a process. And there are some APIs must be included in any interface of an operating system: create destroy wait miscellaneous control, most OS provide some kind of method to suspend a process and resume it. status, there are usually interfaces to get some status information about a process. The first thing that the OS must do to run a program is to load its code and any static data into memory, into the address space of the process. Once the code and static data are loaded into memory, there are a few other things the OS needs to do before running the process. Some memory must be allocated for the program’s run-time stack, and the OS may also allocate smoe memory for the program’s heap. Also, the os will do some other intialization tasks, particularly as related to I/O, i.e. in Unix systems each process by default has three open file descriptors, for standard input, output and error. ...

Amortization Implementations with good amortized bounds are often simpler and faster than implementations with comparable worst-case bounds. Given a sequence of operations, we may wish to know the running time of the entire sequence, but not care about the running time of any individual operation. For instance, given a sequence of n operations, we may wish to bound the total running time of the sequence by O(n) without insisting than every individual operation run in O(1) time. We might be satisfied if a few operations run in O(log n) or even O(n) time, provided the total cost of the sequence is only O(n). This freedom opens up a wide design space of possible solutions, and often yields new solutions that are simpler and faster than worst-case solutions with equivalent bounds. ...

Introduction To implement data structure in a functional way, there are two basic problems. First, from the point of view of designing and implementing efficient data structures, functional programming’s stricture against destructive updates(i.e. assignments) is a staggering handicap, tantamount to confiscating a master chef’s knives. Imperative data structures often rely on assignments in crucial ways, and so different solutions must be found for functional programs. The second difficulty is that functional data strcutures are expected to be more flexible than their imperative counterparts. In particular, when we update an imperative data structure we typically accept that the old version of the data strcuture will no longer be available, but when we update a functional data structure, we expect that both the old and the new version of the data structure will be available for further processing, this is called persistent, while the other is called ephemeral. And we are not surprised if the persistent version is more complicated and even less efficient that the ephemeral one. ...

The Address Space The address space is the abstraction that OS is providing to the running program. The address space of a process contains all of the memory state of the running program. For example, the code of the program, the stack and the heap. In the sight of the program, it loaded into at a particular address and has a potentially very large address space, thus, we say that the OS is virtualizing memory. ...

Linking Linking is the process of collecting and combining various pieces of code and data into a single file that can be loaded (copied) into memory and executed. Linking can be performed at compile time, when the source code is translated into machine code; at load time, when the program is loaded into memory and executed by the loader; and even at run time, by application programs. On modern systems, linking is performed automatically by programs called linkers. ...

Optimization Writing an efficient program requires several type of activities. First, we must select an appropriate set of algorithms and data structures. Second, we must write source code that the compiler can effectively optimize to turn into efficient executable code. A third technique for dealing with especially demanding computations is to divide a task into portions that can be computed in parallel, on some combination of multiple cores and multiple processors. ...

Assembler Computer execute machine code, sequences of bytes encoding the low-level operations that manipulate data manage memory, read and write data on storage devices, and communicate over networks. We will focus on x86-64, the commonest machine language used in processor with laptop and PC, also it’s widely used in supercomputer and lager data center. the x86-64 machine code is much different with the corresponding C code, the processor states below are everywhere: ...

Hardware Organization of A System A typical system has those hadrware below: Buses: Running throughout the system is a collection of electrical conduits called buses that carry bytes of ingormation back and forth betweent the components. Buses are typically designed to transfer fiexed sized chunks of bytes know as words. The number of bytes in a word is a fundamental system parameter that varies across systems. Most have word sizes of 8 bytes (64 bits)today ...