What is computerarchitecture? What does “architecture” mean? Layout and interactions of a computer system What is a computer system? Input Process Output Can a computer system be more than one computer? Think of an example...
Major Components of a Computer Central Processing Unit (CPU) Random Access Memory (RAM) Hard Drive / Disk
ON-OFF-ON-ON 1 0 1 1 Several ways to remember the state of a switch: Electrical – RAM, flash memory Magnetic – Hard drives, magnetic tapes Optical – CDs, DVDs
What does memory look like? Address Data Memory ~ RAM 0 36 Looks like a table 1 3765 Address and Data 2 786 Address is the 3 356 location 4 252 Data is the actual 5 67980 value 6 2355 Memory stores both 7 4234 data and assembly 8 3466 instructions
Central Processing Unit (CPU) Also called the “chip” or “processor” The brain of the Control Address Bus Unit computer Memory Major components: ALU Arithmetic Logic Unit Data Bus (ALU) calculator Control unit controls the calculator Communication bus systems What’s a bus?!?
Fetch-Execute Cycle1. Fetch instruction from memory2. Decode instruction in Control Address Bus control unit Unit Memory3. Execute instruction (data ALU Data Bus may be fetched from memory)4. Store results if necessary5. Repeat!
Registers Temporary storage containers used inside the CPU Extremely fast Fixed size, usually multiples of 8-bits Also called a “word” Example: 32-bit machines (4-byte words) How large is a word in a 64-bit machine?
Cache Slower than registers Faster than RAM Located in front of main RAM Different levels of cache Level1 (L1) and Level2 (L2) Size is usually around 1 MB
CD/DVDs Lands and pits used to represent binary Optical medium - lasers and refraction used to read lands and pits
Direct Access also known as “random access” No need to go through other data to get the data you want We already know where the data is, so we just get it “Magic data retrieval” – no movement/motion Example: registers, cache, RAM
Sequential Access also known as “serial-access” Data is ordered in some sequential fashion To get to your data, you need to go through other data in front of it Example: Fast-forwarding through a tape to get to the song you want
Direct-Access vs. Sequential Access Direct-Access: Advantage: fast access Disadvantage: data cannot be accessed in sequential or sorted order Data is placed randomly on the disk Accessing things in order then requires an index file Slower when trying to access sequential data that is not already in order (back-and-forth-and-back-and-forth) Example: hard drives (disks) Sequential Access Advantage: Simple to organize (already in some sequential order) Disadvantage: Slow when accessing specific things in no order Example: magnetic tape backups Could we implement sequential access using a hard disk?