《计算机科学导论》
forth edition
Introduction
Turing Model
what computer model can be described?
- a basic data processor
- input data
- computer
- output data
basic data process can only handle specific computation, we need genneral model
- a general data processor (a programmable data processor)
- input data
- computer
- a program, a set of instructions that tells computer what to do with data
- output data
This is turing model. It can do same thing with modern computer, if it has same input and same program
Number System
Introduction
A number system defines how a nubmer can be rrepresented using distinct symbols.
Positional Number System
The postion a symbol occupies in the number determines the value it represents
NoPositional Number System
Still uses a limited number of symbols in which number of symbols in which each symbol has a value. However, the position a symbol occupies in the number normally bears no relation ot its value.
Data Storage
As discussed before, a computer is a programmable data processing machine. Before
we can talk about processing data, we need to understand the nature of data.
Data Types
Data today come in different forms including numbers, text, audio, images, and video
Data inside the computer
All data types are transformed into a uniform representation when they are stored in a
computer and transformed back to their original form when retrieved. This universal
representation is called a bit pattern
Bits
A bit represents the state of a device that can take one of two states.
For example, a switch can be on or off.
Bit patterns
To represent different types of data, we use a bit pattern, a sequence, or as it is
sometimes called, a string of bits.
Operating Systems
Introduction
Evolution
Components
A modern operating system has at least four duties: memory manager, process manager, device manager, and file manager.
Like many organizations that have a department that is not necessarily under any specific manager, an operating system also has such a component,
which is usually called a user interface or a shell. The user interface is responsible for communication outside the operating system.