Topic 6: Further System Fundamentals

Fetch-Execute Cycle Review

Computer programs are instructions stored in RAM Processor fetches instructions and executes them Fetch Decode Execute Memory (store results) Repeat!

CPU Diagram

Additional CPU Components

Program counter (PC) Holds the address of the next instruction in the

program sequence Instruction register

Holds the operation code of the type of instruction to be executed (e.g. ADD, SUB)

Accumulator ALU’s internal register that holds ongoing total

Fetch-Execute Again

1. Fetch instruction from the address stored in the program counter

2. Store instruction in instruction register3. Decode instruction register4. Execute operation (control unit tells ALU

what to do)5. ALU performs operation and uses its

accumulator to remember result6. Store accumulator result back to memory

Interrupts

Things that “interrupt” the processor’s normal operation

Handle events and exceptions Keyboard input Null pointer exception etc.

Special code exists to handle instructions, which is also stored in RAM

Interrupt Register

Stores the offset address of the special interrupt handling code Interrupt Code Address = Base Address + Interrupt Register

Bus Review

Bus = set of parallel wires Brings data from one place to another place

CPU cache RAM address bus data bus

Hard Drives

read/write head The part of the arm that touches the disk to read/write

block size Number of bytes that are read/written in a single read of

write operation track

Ring around a disk platter cylinder

The set of corresponding tracks from all platters sector

Section of a track

Disk Latency

What are the two moving parts of a disk? Platter spinning around ~ rotational delay (sector

wait time) Arm w/ head moving across platter (track seek

time) How long does it take to access something

on the disk?Access time = track seek time + sector wait time

Operating System

Controls operation of the computer system OS functions:

Input/Output control File management Resource management (CPU, memory) Security User interface

Linker, Loader, Library Manager Linker

Links compiled object code modules E.g. import java.io.* is linked to your program

Loader Loads linked object code into memory to run

Library Manager Manages library functions used by linker

More Network Stuff

Modes of communication Telephone lines ~ dialup Coaxial cable ~ cable internet Twisted pair ~ ethernet Fiber-optic ~ FIOS Microwave (high frequency radio) ~ wifi Satellite

Packet Switching

Break data up into packets & transmit Individual packets are not all necessarily

transmitted through the same links Each packet travels over the best available

link at the time Packets may arrive at destination out of order

must be re-ordered and reassembled (protocol!)

Network Security

User logins Must be an authenticated user to login Password, smartcard, fingerprint, iris, etc.

Layered access via permissions Different levels of user access

Firewall Inspect and filter incoming traffic

Encryption Encrypt data so that it is unreadable by outsiders