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 register 3. Decode instruction register 4. Execute operation (control unit tells ALU what to do) 5. ALU performs operation and uses its accumulator to remember result 6. 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