File System Def. File System: a layer of OS that transforms block interface of disks (or other block devices) into files, directories, etc… Components: naming: interface to find files by name, not b

I/O Devices The old architecture of computer IO Figure 1: The old architecture of computer IO The modern architecture of computer IO Figure 2: The modern architecture of computer IO A sim

Def. Query processing refers to activities (DBMS) extracting data from DB, including translation of queries in DB language into expressions that can be used at the physical level of the system SQL

Readers/Writers Problem Motivation: Consider a shared database. Two classes of users: Readers - never modify database. Writers - read and modify database. Is using a single lock on the whole dat

Basic Concepts Def. Search key is an attribute or a set of attributes used to look up records. Why we need indexing mechanisms. We create a DB indexed file instructor and its index file. The file in

File Organization DB is stored as a collection of DB files. Each file is a sequence of records. Each record is in a sequence of fields. Each relation table is a set of tuples. The record size is fix

Naive Use of Interrupt Enable/Disable On a unified-processor, can avoid context switching by: avoiding internal events preventing external events by disabling interrupts Consequently, naive impleme

表示学习的动机 直接使用原始特征，此时特征比较单一，需要进行非线性组合才能发挥其作用。 一些特征之间可能存在相关性。 并不是所有的特征都对预测有用。 特征中存在噪声。 特征纬度过高，会导致维度灾难。 主成分分析（回顾） Def. 方差：描述一维变量偏离其均值的程度 \[ \sigma^{2} = \frac{1}{N} \sum_{i = 1}^{N} (X_i - \overline{

OS Programming Interface What are the system calls? They differ from different operating system. The follow table shows some system calls in Windows and Unix. Windows Unix Process Control C

*User to kernel Mode Switch There are three conditions will trigger switch. Exceptions: When the processor encounters unexpected condition like illegal memory access, divide-by-zero (in C), perform