Computer-System Structure

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Chapter 2 Computer-System Structure

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Computer-System Structure

Objective: General knowledge of the structure of a computer system.

printer CPU

printer controller

memory controller

disk controller

memory

tape-drive controller

disks tape drivers

Device controllers: synchronize and manage access to devices.

Booting

Bootstrap program:

Initialize all aspects of the system, e.g., CPU registers, device

controllers, memory, etc.

Load and run the OS

Operating system: run init to initialize system processes, e.g., various daemons, login processes, after the kernel has been bootstrapped.

(/etc/rc* & init or /sbin/rc* & init)

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Interrupt

Hardware interrupt, e.g. services requests of I/O devices

Software interrupt, e.g. signals, invalid memory access, division by zero, system calls, etc – (trap)

Procedures: generic handler or interrupt vector (MS-DOS,UNIX) process execution

interrupt

handler return

Interrupt Handling Procedure

Saving of the address of the interrupted instruction: fixed locations or stacks

Interrupt disabling or enabling issues: lost interrupt?!

prioritized interrupts Æ masking interrupted process

system stack fixed address

per interrupt type

interrupted address, registers ...

handler

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Interrupt Handling Procedure

Interrupt Handling

Î Save interrupt information

Î OS determine the interrupt type (by polling) Î Call the corresponding handlers

Î Return to the interrupted job by the restoring important information (e.g., saved return addr. Æ program counter)

indexed by a unique

device number

Interrupt Vector

0 1

n

--- --- --- --- --- ---

--- --- ---

Interrupt Handlers (Interrupt Service Routines)

I/O Structure

The device drivers are responsible of moving data between the peripheral devices and their local buffer storages.

printer

CPU printer

controller

memory controller

DMA

memory

tape-drive controller

disk

tape drivers

registers buffers registers buffers

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I/O Structure

I/O operation

a. CPU sets up specific controller registers within the controller.

b. Read: devices Æ controller buffers Æ memory

Write: memory Æ controller buffers Æ devices

c. Notify the completion of the operation by triggering an interrupt

I/O Types

I/O system call

wait till the

completion •wait instruction (idle till interrupted)wait

•looping

•polling

•wait for an interrupt or

or a. Synchronous I/O

Issues: overlapping of computations and IO activities, concurrent I/O activities, etc.

Loop: jmp Loop

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I/O types

b. Asynchronous I/O

sync

wait till the completion wait mechanisms!!

*efficiency

I/O Types

Hardware data transfer Interrupt handler

Device driver Requesting process

Hardware data transfer Interrupt handler

Device driver Requesting process

user

Kernel user

Kernel

Synchronous I/O

Time Time

Asynchronous I/O wait

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I/O Types

A Device-Status Table Approach

card reader 1 status: idle line printer 3 status: busy disk unit 3 status: idle

........

Request addr. 38596 len?1372 Request file:xx Record Addr. len

Request file:yy Record Addr. len

process 1 process 2

•Tracking of many I/O requests

•type-ahead service

DMA

Goal: Release CPU from handling excessive interrupts!

E.g. 9600-baud terminal

2-microsecond service / 1000 microseconds

High-speed device:

2-microsecond service / 4 microseconds

Procedure

Execute the device driver to set up the registers of the DMA controller.

DMA moves blocks of data between the memory and its own buffers.

Transfer from its buffers to its devices.

Interrupt the CPU when the job is done.

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Storage Structure

Access time: a cycle

Access time:

several cycles

Access time: many cycles

memory

Magnetic Disks registers

cache

CD-ROMs/DVDs Jukeboxes Tertiary Storage

•removable media

Secondary Storage

•nonvolatile storage

HW-Managed

SW-Managed

Primary Storage

•volatile storage

CPU

* Differences:

Size, Cost, Speed, Volatility

Memory

Processor can have direct access!

Intermediate storage for data in the registers of device controllers

Memory-Mapped I/O (PC & Mac) (1)Frequently used devices

(2)Devices must be fast, such as video controller, or special I/O instructions is used to move data between

memory & device controller registers

Programmed I/O – polling

or interrupt-driven handling

R1 R2

R3 . . .

Memory

Device Controller

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Magnetic disks

Transfer Rate

Random- Access Time

Seek time in x ms

Rotational latency in y ms

60~200 times/sec spindle

sector

cylinder

platter

r/w head

disk arm arm assembly track

Magnetic Disks

Disks

Fixed-head disks:

More r/w heads v.s. fast track switching

Moving-head disks (hard disk)

Primary concerns:

Cost, Size, Speed

Computer Æ host controller Æ disk controller Æ disk drives (cache ÅÆ disks)

Floppy disk

slow rotation, low capacity, low density, but less expensive

Tapes: backup or data transfer bet machines

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Storage Hierarchy

register

Main Memory Electronic Disk

Magnetic Disk Optical Disk

Cache

Magnetic Tape

Cost

High hitting rate

• instruction & data cache

• combined cache

Faster than magnetic disk – nonvolatile?!

Alias: RAM Disks

Sequential Access XX GB/350F

Speed

Volatile Storage

Storage Hierarchy

Caching

Information is copied to a faster storage system on a temporary basis

Assumption: Data will be used again soon.

Programmable registers, instr. Cache, etc.

Cache Management

Cache Size and the Replacement Policy

Movement of Information Between Hierarchy

Hardware Design & Controlling Operating Systems

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Storage Hierarchy

Coherency and Consistency

Among several storage levels (vertical)

Multitasking vs unitasking

Among units of the same storage level , (horizontal), e.g. cache coherency

Multiprocessor or distributed systems

Memory Cache CPU

Memory cache CPU

Hardware Protection

Goal:

Prevent errors and misuse!

E.g., input errors of a program in a simple batch operating system

E.g., the modifications of data and code segments of another process or OS

Dual-Mode Operations – a mode bit

User-mode executions except those after a trap or an interrupt occurs.

Monitor-mode (system mode, privileged mode, supervisor mode)

Privileged instruction:machine instructions that may cause harm

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Hardware Protection

System Calls – trap to OS for executing privileged instructions.

Resources to protect

I/O devices, Memory, CPU

I/O Protection (I/O devices are scare resources!)

I/O instructions are privileged.

User programs must issue I/O through OS

User programs can never gain control over the computer in the system mode.

Hardware Protection

Memory Protection

Goal: Prevent a user program from modifying the code or data structures of either the OS or other users!

Instructions to modify the memory space for a process are privileged.

kernel job1

……

job2

…… Limit register

Base register Ù Check for every memory address by hardware

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Hardware Protection

CPU Protection

Goal

Prevent user programs from sucking up CPU power!

Use a timer to implement time-sharing or to compute the current time.

Instructions that modify timers are privileged.

Computer control is turned over to OS for every time-slice of time!

Terms: time-sharing, context switch

Network Structure

Local-Area Network (LAN)

Characteristics:

Geographically distributed in a small area, e.g., an office with different computers and peripheral devices.

More reliable and better speed

High-quality cables, e.g., twisted pair cables for 10BaseT Ethernet or fiber optic cables for 100BaseT Ethernet

Started in 1970s

Configurations: multiaccess bus, ring, star networks (with gateways)

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Network Structure

Wide-Area Network (WAN)

Emerged in late 1960s (Arpanet in 1968)

World Wide Web (WWW)

Utilize TCP/IP over ARPANET/Internet.

• Definition of “Intranet”: roughly speaking for any network under one authorization, e.g., a company or a school.

•Often in a Local Area Network (LAN), or connected LAN’s.

• Having one (or several) gateway with the outside world.

• In general, it has a higher bandwidth because of a LAN.

Network Structure – WAN

gateway

gateway TARNET

TARNET

HINET HINET

Intranet A Intranet AIntranet

A Intranet AIntranet Intranet

Intranet Intranet

router Intranet

Intranet

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Network Structure – WAN

Router

With a Routing table

Use some routing protocol, e.g., to maintain network topology by broadcasting.

Connecting several subnets (of the same IP-or- higher-layer protocols) for forwarding packets to proper subnets.

Gateway

Functionality containing that of routers.

Connecting several subnets (of different or the same networks, e.g., Bitnet and Internet)for forwarding packets to proper subnets.

Network Structure – WAN

Connections between networks

T1: 1.544 mbps, T3: 45mbps (28T1)

Telephone-system services over T1

Modems

Conversion of the analog signal and digital signal

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Network Layers in Linux

PPP SLIP Ethernet

Internet Protocol (IP)

Network Layer ARP

TCP UDP

INET sockets

BSD sockets Kernel

Applications applications

TCP/IP

IP Address:

140.123.101.1

256*256*256*256 combinations

140.123 -> Network Address

101.1 -> Host Address

Subnet:

140.123.101 and 140.123.102

Mapping of IP addresses and host names

Static assignments: /etc/hosts

Dynamic acquisition: DNS (Domain Name Server)

/etc/resolv.confg

If /etc/hosts is out-of-date, re-check it up with DNS!

Domain name: cs.ccu.edu.tw as a domain name for 140.123.100, 140.123. 101, and 140.123.103

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TCP/IP

Transmission Control Protocol (TCP)

Reliable point-to-point packet transmissions.

Applications which communicate over TCP/IP with each another must provide IP addresses and port numbers.

/etc/services

Port# 80 for a web server.

User Datagram Protocol (UDP)

Unreliable point-to-point services.

Both are over IP.

TCP/IP

Mapping of Ethernet physical addresses and IP addresses

Each Ethernet card has a built-in Ethernet physical address, e.g., 08-01-2b-00-50-A6.

Ethernet cards only recognize frames with their physical addresses.

Linux uses ARP (Address Resolution

Protocol) to know and maintain the mapping.

Broadcast requests over Ethernet for IP address resolution over ARP.

Machines with the indicated IP addresses reply with their Ethernet physical addresses.

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TCP/IP

TCP header + Data

IP header Data

Ethernet header Data

An Ethernet frame

An IP packet

A TCP packet

• Each IP packet has an indicator of which protocol used, e.g., TCP or UDP

Computer-System Structure

Contents

Chapter 2