intro to computer systems summer 2014 comp 2130 introduction to computer systems computing science...

Intro to Computer Systems

Summer 2014

COMP 2130 Introduction to Computer Systems

Computing ScienceThompson Rivers University

TRU-COMP2130 Intro to Computer Systems 2

Course Objectives

The better knowledge of computer systems, the better programing.Computer System C Programming Language

Computer architectureCPU (Central Processing Unit)IA32 assembly language

Introduction to C language

Compiling, linking, loading, executing

Physical main memoryMMU (Memory Management Unit)

Virtual memory space

Memory hierarchyCache

Dynamic memory management

Better coding – locality

Reliable and efficient programming for power programmers(to avoid strange errors, to optimize codes, to avoid security holes, …)


Course Contents

Introduction to computer systems: B&O 1, 9.1 – 9.2 Introduction to C programming: K&R 1 – 4 Data representations: B&O 2.1 – 2.4 C: advanced topics: K&R 5.1 – 5.9, 5.11, 6 – 8 Introduction to IA32 (Intel Architecture 32): B&O 3.1 – 3.8, 3.13 Compiling, linking, loading, and executing: B&O 7 (except 7.12) Dynamic memory management – Heap: B&O 9.9.1 – 9.9.2, 9.9.4 –

9.9.5, 9.11 Code optimization: B&O 5.1 – 5.6, 5.13 Memory hierarchy, locality, caching: B&O 5.12, 6.1 – 6.3, 6.4.1 –

6.4.2, 6.5, 6.6.2 – 6.6.3, 6.7 Virtual memory (if time permits): B&O 9.4 – 9.5


Unit Learning Objectives

List the four phases in the compilation system. List the four major hardware components. List the three major components in CPU. Explain the logical concepts of main memory. List the two steps in an instruction cycle. Explain briefly for what and how PC is used. Explain briefly what locality means. Give an example code that can be executed fast by using cache

memory. Define what a process is. Explain how process and thread are different. Define what multi-processing is. Distinguish virtual memory and physical memory.


Explain what heap in the virtual memory space is. Explain what stack in the virtual memory space is. Name the hardware component that translates virtual addresses to

physical addresses. …


Unit Contents

What is information? Programs and compilation systems CPU Cache Memory hierarchy Operating systems Communications


Introduction

A computer system consists of1. H…

2. S…

that work together to run … Hardware affects the CORRECTNESS and PERFORMANCE of

programs.


1. What is Information?

A source program (or source file) – a sequence of bits?#include <stdio.h>

int main()

{

printf(“Hello, world\n”);

}

Bits ??? Bytes ??? ASCII code ???

For each character, a unique byte-sized integer is assigned. Text file ??? Binary file ??? But files are files for operating systems.


Where are files (or data) stored in a computer system? How is information different from data? The only thing that distinguishes different data objects is the context

in which we view. A data object can be interpreted in different ways. E.g., the same sequence of bytes might represent

integer, floating-point number (???), character string, machine instruction, …

As programmers, we need to understand machine representations of numbers. Details in B&O 2.


2. Programs and Compilation Systems

Can a computer system understand a high-level C program? A high-level C program translated to low-level machine-language

instructions packaged in a form called executable object program and stored as a binary file. Object programs are also referred as object files.

How to translate? Compilers

gcc (or cc)


The compilation system

Preprocessing phase #include <stdio.h> #define PI 3.141593

Compilation phase Assembly phase Linking phase

hello is ready to be loaded into main memory and executed. Being loaded into main memory Being executed

Pre-processor(cpp)

hello.i Compiler(cc1)

hello.s Assembler(as)

hello.o Linker(ld)

hellohello.c

Sourceprogram(text)

Modifiedsourceprogram(text)

Assemblyprogram(text)

Relocatableobjectprograms(binary)

Executableobjectprogram(binary)

printf.o


Compilation systems try to produce correct and efficient machine codes, but lists the errors which it could not understand

Reasons to understand how the compilation systems work Optimizing program performance

Not easy for them to optimize source codes Understanding link-time errors

Especially in the development of a large software system Avoiding security holes

Run-time errors


3. CPU

CPU stands for Central Processing Unit Let’s discuss how CPU is used to run programs. Shell, a special application program called a command-line

interpreter, accepts commands from the user and execute them. What happens to hello program when we run?

Hardware Organization of a System

What happens to hello program when we run? Need to understand the hardware organization that consists of

4 major components: CPU, main memory, buses, i/o devices

Mainmemory

I/O bridge

Bus interface

ALU

RegistersCPU

System bus Memory bus

Disk controller

Graphicsadapter

USBcontroller

MouseKeyboard Display

Disk

I/O bus Expansion slots forother devices suchas network adapters

hello executable stored on disk

PC

Buses Carry fixed-size bytes known as words 4 bytes (32bits) or 8 bytes (64bits)

I/O devices Main memory

DRAM Logically a linear array of addressable bytes, each with its own unique

address starting at zero CPU (…), or simply processor

Register files, or simply registers A register is a word-sized storage device.

PC (Program Counter) A special register pointing at (contains the address of) some machine-language

instruction stored in main memory; increased after the fetch cycle ALU (???)

Compute new data and address values

Only one instruction in main memory, which is pointed by PC, is read (called fetched) by CPU and executed, not multiple instructions. This is called instruction cycle.

PC is increased after the instruction fetch so that the next instruction is pointed by PC and read by CPU.

Hence programs have to be loaded into main memory to be executed. How to start after the program is loaded into memory?

PC must be updated to the address of the first instruction in the program.

PC is updated.


Running the hello Program

What happens to hello program when we run?


Mainmemory

I/O bridge

Bus interface

ALU

Registers

CPU


Disk controller

Graphicsadapter

USBcontroller


Disk


PC

“./hello"

Usertypes

“./hello"

Shell is reading “.\hello” using the services providedby OS.


Mainmemory

I/O bridge

Bus interface

ALU

Registers

CPU


Disk controller

Graphicsadapter

USBcontroller


Disk



PC

hello code

"hello,world\n"

Shell is loading “.\hello”using the services providedby OS.


Mainmemory

I/O bridge

Bus interface

ALU

Registers

CPU


Disk controller

Graphicsadapter

USBcontroller


Disk



PC

hello code

"hello,world\n"

"hello,world\n"

“.\hello” is now running.Shell then?


4. Cache

From the previous example, we can see that a system spends a lot of time moving information from one place to another.

It might take CPU 10 M times longer to read a word from disk than from main memory. This is why hello is loaded into memory before the file is executed by CPU.

How is hello executed? hello consists of machine instructions. Only one instruction pointed by PC is read (called fetched) by CPU and

executed, not multiple instructions. This is called instruction cycle. Fetch time is much longer than execution time.

PC is updated.


Fetch time is much longer than execution time. Any good idea to solve this processor-memory gap?

Hint: The processor can read data from registers almost 100 times faster than from memory.


Smaller faster and closely located storage device called cache memory, or simply cache

Multiple levels could be possible: E.g., L1, L2, L3 How is cache helpful? Programs will be loaded into cache, not memory?

Initially programs will be loaded into main memory. Locality – the tendency for programs to access frequently data and code

in localized regions; any example code? Important for code optimization

Mainmemory

I/Obridge

Bus interface

ALU

RegistersCPU chip

System busMemory bus

Cache memories

for (i=0; i<100; i++) sum += i;


5. Memory Hierarchy

Regs

L1 cache

Main memory(DRAM)

Local secondary storage(local disks)

Larger, slower,

and cheaper (per byte)storagedevices

Remote secondary storage(distributed file systems, Web servers)

Local disks hold files retrieved from disks on remote network servers.

Main memory holds disk blocks retrieved from local disks.

L2 cache (SRAM)

L1 cache holds cache lines retrieved from the L2 cache.

CPU registers hold words retrieved from cache memory.

L2 cache holds cache linesretrieved from L3 cache

L0:

L1:

L2:

L3:

L4:

L5:

Smaller,faster,and

costlier(per byte)storage devices

L3 cache (SRAM) L3 cache holds cache

linesretrieved from memory.

L6:

25

6. Operating Systems

When the shell loaded and ran the hello program, and when the hello program printed its message, neither program actually accessed the keyboard, display, disk, or main memory directly.

Then how? Services including I/O are provided by the operating system.

Application programs

Processor Main memory I/O devices

Operating systemSoftware

Hardware

Processor Main memory I/O devices

Processes

Files

Virtual memory


Processes

A process is the operating system’s abstract for a running program. Multiple processes can run on the system? (We assume one CPU core.)

Logically yes. In the previous example, shell and hello programs. But this is not real parallel processing. This is called multi-processing. The instructions of one process are interleaved with the instructions of

another process, using context switching. (all the register values + …)

Process A Process B

User code

Kernel code

User code

Kernel code

User code

Time

Context switch

Context switch

read

Disk interrupt

Return from read


Threads

A process can consists of multiple execution units, called threads or light-weight processes, each running in the context of the process and sharing the same code and global variables, but different local variables.

Very important programming model. Any good example application?


Virtual Memory

A program includes instructions and data, and they will be loaded into memory. The addresses of instruction and data are used in the program. E.g., x = y + 10;

Multiple processes should share the fixed-size memory. When a program is loaded next time, the location of the program in memory will be probably different.

How to assign memory space to each process? How to let a process (i.e., machine codes) know its location in

memory? If processes have to know their location in memory to access

variables, programming would become a very difficult job. Do you think in which area in memory you would put variables? How to solve this problem?

Virtual (oac logical) address space and physical address space

TRU-COMP2130 29

Virtual memory is an abstraction that provides each process with the illusion that it has exclusive use of main memory.

Each process has the same uniform view of memory, which is known as its virtual address space.

Now compilers can compile programs to machine-level instructions. (All instructions in programs use virtual addresses.)

Kernel virtual memory

Memory mapped region forshared libraries

Run-time heap(created by malloc)

User stack(created at runtime)

0

Memoryinvisible touser code

Read/write data

Read-only code and data

Loaded from the hello executablefile

printf function

0x08048000 (32)0x00400000 (64)

Intro to Computer Systems


Program code and data Machine instructions Global variables

Heap Dynamic memory allocation – malloc(), free(), …

Shared libraries Shared by multiple process – e.g., C standard library, the math library, …

Stack To allocate memory for parameters and local variables as functions are

called Kernel virtual memory

The part of the operating system Always resident in memory


Multiple processes have program code and data within the same virtual address space.

But they are loaded in different locations in the physical memory.


Multiple processes have program code and data within the same virtual address space.

But they are loaded in different locations in the physical memory. Here is a very critical problem. The program code, i.e., machine

instructions, uses virtual addresses in the virtual address space, and the actual code and data are loaded in different physical addresses. When an instruction is fetched and executed by CPU, virtual addresses are used. E.g., pointing to a variable uses the virtual address of the variable, which is different from the physical address of the variable in memory. CPU would access wrong location in the physical memory.

How to solve? MMU (Memory Management Unit) – hardware component to translate

virtual addresses to physical addresses


Example


7. Communications

Mainmemory

I/O bridge

Bus interface

ALU

Registers

CPU chip


Disk controller

Graphicsadapter

USBcontroller

Mouse Keyboard Monitor

Disk

I/O bus

Expansion slots

Networkadapter

Network

PC


Localtelnetclient

Remotetelnetserver

2. Client sends "hello"string to telnet server 3. Server sends "hello"

string to the shell, which runs the hello program,

and passes the outputto the telnet server4. Telnet server sends

"hello, world\n" stringto client

5. Client prints"hello, world\n"

string on display

1. User types"hello" at the

keyboard

intro to computer systems summer 2014 comp 2130 introduction to computer systems computing science...

Documents

computer systemssummer

introductiona computer

physical memory

cache memory

dynamic memory management

virtual addresses

information different

different data objects