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# 计算机代写|OS操作系统代考OS operating system代写|CS161 Caching

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## 计算机代写|OS操作系统代考OS operating system代写|Caching

In order to understand caching, you have to understand how computers execute programs. For a deep understanding of this topic, you should study computer architecture. My goal in this chapter is to provide a simple model of program execution.

When a program starts, the code (or text) is usually on a hard disk or solid state drive. The operating system creates a new process to run the program, then the loader copies the text from disk into main memory and starts the program by calling main.

While the program is running, most of its data is stored in main memory, but some of the data is in registers, which are small units of memory on the CPU. These registers include:

The program counter, or PC, which contains the address (in memory) of the next instruction in the program.

The instruction register, or IR, which contains the instruction currently executing.

The stack pointer, or SP, which contains the address of the stack frame for the current function, which contains its parameters and local variables.

General-purpose registers that hold the data the program is currently working with.

A status register, or flag register, that contains information about the current computation. For example, the flag register usually contains a bit that is set if the result of the previous operation was zero.

## 计算机代写|OS操作系统代考OS operating system代写|Cache performance

The solution to this problem, or at least a partial solution, is caching. A cache is a small, fast memory on the same chip as the CPU. In current computers, a cache might be $1-2 \mathrm{MiB}$, and the access time might be $1-2 \mathrm{~ns}$.

When the CPU loads a value from memory, it stores a copy in the cache. If the same value is loaded again, the CPU gets the cached copy and doesn’t have to wait for memory.

Eventually the cache gets full. Then, in order to bring something new in, we have to kick something out. So if the CPU loads a value and then loads it again much later, it might not be in cache any more.

The performance of many programs is limited by the effectiveness of the cache. If the data the CPU needs is usually in cache, the program can run at the full speed of the CPU. If the CPU frequently needs data that is not in cache, the program is limited by the speed of memory.

The cache hit rate, $h$, is the fraction of memory accesses that find data in cache; the miss rate, $m$, is the fraction of memory accesses that have to go to memory. If the time to process a cache hit is $T_h$ and the time for a cache miss is $T_m$, the average time for each memory access is
$$h T_h+m T_m$$
Equivalently, we could define the miss penalty as the extra time to process a cache miss, $T_p=T_m-T_h$. Then the average access time is
$$T_h+m T_p$$
When the miss rate is low, the average access time can be close to $T_h$. That is, the program can perform as if memory ran at cache speeds.

. sh

## 计算机代写|操作系统操作系统代考操作系统代写|缓存性能

. sh 这个问题的解决方案，或者至少是部分解决方案，是缓存。缓存是与CPU位于同一芯片上的小而快速的内存。在当前计算机中，缓存可能是$1-2 \mathrm{MiB}$，访问时间可能是$1-2 \mathrm{~ns}$ .

$$h T_h+m T_m$$

$$T_h+m T_p$$

## MATLAB代写

MATLAB 是一种用于技术计算的高性能语言。它将计算、可视化和编程集成在一个易于使用的环境中，其中问题和解决方案以熟悉的数学符号表示。典型用途包括：数学和计算算法开发建模、仿真和原型制作数据分析、探索和可视化科学和工程图形应用程序开发，包括图形用户界面构建MATLAB 是一个交互式系统，其基本数据元素是一个不需要维度的数组。这使您可以解决许多技术计算问题，尤其是那些具有矩阵和向量公式的问题，而只需用 C 或 Fortran 等标量非交互式语言编写程序所需的时间的一小部分。MATLAB 名称代表矩阵实验室。MATLAB 最初的编写目的是提供对由 LINPACK 和 EISPACK 项目开发的矩阵软件的轻松访问，这两个项目共同代表了矩阵计算软件的最新技术。MATLAB 经过多年的发展，得到了许多用户的投入。在大学环境中，它是数学、工程和科学入门和高级课程的标准教学工具。在工业领域，MATLAB 是高效研究、开发和分析的首选工具。MATLAB 具有一系列称为工具箱的特定于应用程序的解决方案。对于大多数 MATLAB 用户来说非常重要，工具箱允许您学习应用专业技术。工具箱是 MATLAB 函数（M 文件）的综合集合，可扩展 MATLAB 环境以解决特定类别的问题。可用工具箱的领域包括信号处理、控制系统、神经网络、模糊逻辑、小波、仿真等。