Chapter One 1.1~1.4 _Computer Abstractions and Technology

1.1

• Software as a Service

(SaaS) delivers software and data as a service over the Internet, usually via a thin program such as a browser that runs on local client devices, instead of binary code that must be installed, and runs wholly on that device. Examples include web search and social networking.

keyword:

• hierarchical nature of memories
• sequential processing to parallel processing
• “multicore” microprocessors

1.2

Eight great ideas in computer architecture:

1. Design for Moore’s Law

It states that integrated circuit resources double every 18–24 months.

2. Use Abstraction to Simplify Design

Lower-level details are hidden to offer a simpler model at higher levels.

3. Make the Common Case Fast

Making the common case fast will tend to enhance performance better than optimizing the rare case

4. Performance via Parallelism

5. Performance via Pipelining

6. Performance via Prediction

In some cases it can be faster on average to guess and start working rather than wait until you know for sure

7. Hierarchy of Memories

The fastest, smallest, and most expensive memory per bit at the top of the hierarchy and the slowest, largest, and cheapest per bit at the bottom.

8. Dependability via Redundancy(通过冗余提高可靠性）

we make systems dependable by including redundant components that can take over when a failure occurs and to help detect failures

1.3

An operating system interfaces between a user’s program and the hardware and provides a variety of services and supervisory functions.
Among the most important functions are:

■ Handling basic input and output operations

■ Allocating storage and memory

■ Providing for protected sharing of the computer among multiple applications using it simultaneously.

keyword

• assembly language
  A symbolic representation of machine instructions.

• machine language
  A binary representation of machine instructions.

FIGURE1.4 .PNG

1.4

Keyword:

• input device
• output device

THE BIG PICTURE

The five classic components of a computer are input, output, memory, datapath, and control, with the last two sometimes combined and called the processor. Figure 1.5 shows the standard organization of a computer.

FIGURE 1.5.PNG

1.4.1 Liquid crystal display(LCDs)

• liquid crystal display
  A display technology using a thin layer of liquid polymers that can be used to transmit or block light according to whether a charge is applied.
• active matrix display
  A liquid crystal display using a transistor to control the transmission of light at each individual pixel.
• pixel
  The smallest individual picture element. Screens are composed of hundreds of thousands to millions of pixels, organized in a
  matrix.

Th e image is composed of a matrix of picture elements, or pixels, which can be represented as a matrix of bits, called a bit map. Depending on the size of the screen and the resolution, the display matrix in a typical tablet ranges in size from 1024 X 768 to 2048 X 1536. A color display might use 8 bits for each of the three colors (red, blue, and green), for 24 bits per pixel, permitting millions of diff erent
colors to be displayed.

F1.6.PNG

Touchscreen
While there are a variety of ways to implement a touch screen, Since people are electrical conductors,many tablets today use capacitive sensing.

1.4.3 opening the box

• integrated circuit
  Also called a chip. A device combining dozens to millions of transistors.

• central processor unit (CPU)
  Also called processor. Th e active part of the computer, which contains the datapath and control and which adds numbers, tests numbers, signals I/O devices to activate, and so on.

• datapath
  The component of the processor that performs arithmetic operations

• control
  The component of the processor that commands the datapath, memory, and I/O devices according to the instructions of the program.

• memory
  The storage area in which programs are kept when they are running and that contains the data needed by the running programs.

• dynamic random access memory (DRAM)
  Memory built as an integrated circuit; it provides random access to any location. Access times are 50 nanoseconds in 2012.

• cache memory
  A small, fast memory that acts as a buff er for a slower, larger memory.

• static random access memory (SRAM)
  Also memory built as an integrated circuit, but faster and less dense than DRAM.

• instruction set architecture
  Also called architecture. An abstract interface between the hardware and the lowest-level soft ware that encompasses all the information necessary to write a machine language program that will run correctly, including instructions, registers, memory access, I/O, and so on.

• application binary interface (ABI)
  The user portion of the instruction set plus the operating system interfaces used by application programmers. It defi nes a standard for binary portability across computers.

The Big Picture

• Both hardware and software consist of hierarchical layers using abstraction, with each lower layer hiding details from the level above. One key interface between the levels of abstraction is the instruction set architecture—the interface between the hardware and low-level software. This abstract interface enables many implementations of varying cost and performance to run identical software.

1.4.4 A Safe Place for Data

• volatile memory Storage
  such as DRAM, that retains data only if it is receiving power.

• nonvolatile memory
  A form of memory that retains data even in the absence of a power source and that is used to store programs between runs.A DVD disk is nonvolatile

• main memory
  Also called primary memory. Memory used to hold programs while they are running; typically consists of DRAM in today’s computers.

• secondary memory
  Nonvolatile memory used to store programs and data between runs; typically consists of flash memory in PMDs and
  magnetic disks in server.

• magnetic disk
  Also called hard disk. A form of nonvolatile secondary memory composed of rotating platters coated with a magnetic

• flash memory
  A nonvolatile semiconductor memory. It is cheaper and slower than DRAM.