1. COMP1321 Digital Infrastructures
Richard Henson
November 2017

2. Week 7: Summary of Concepts covered so far…
Objectives:
explain the main aspects of CPU architecture
explain how a CPU works to process programming instructions
explain motherboard architecture in terms of the various types of digital data storage that communicate with the CPU

3. CPUs
Computer “merely” processes digital data according to digital instructions
CPU very, very, very, fast and getting even faster (Moore’s Law)
Most of motherboard architecture is about speeding up memory storage/retrieval from merely fast to billions of bytes per second!

4. Digital Storage
Fastest storage locations built into the CPU: registers and internal cache
Next fastest mounted directly onto the motherboard: external cache, static RAM, dynamic RAM (primary storage)
CPU can read data directly from RAM, or write data directly to RAM
Devices to get data in and out of RAM known as secondary storage

5. Secondary Storage Hard drives quite fast… especially SSD drives
Connected to motherboard by SATA connections or USB v3 connections
Previous (legacy) connection methods slower: USB v2, PS/2, serial ports, parallel ports

6. Programming a CPU Each CPU family has an instruction set
Most popular: Intel 8086 family (historical)
Programs to tell CPU what to do have to be written to the CPU in language that CPU can understand (assembly language for that CPU family e.g. 8086x)

7. Compilers and Interpreters
Modern programming written in high level languages
Code needs to be converted into assembly language
Two ways to do this:
Compiler… whole program converted into assembly language and saved as “ready to run”
Interpreter… remains as source code (ASCII characters) and one line converted at a time…

8. Hard Drive Storage
Primary storage only stores data on a temporary basis
Hard disks need to keep data stored reliably for long periods even when the power is off, AND allow fast retrieval
Best practice until recently:
Magnetic disks (known as hard drives)
Now use electronic disks (Solid State)

9. Data Organisation on Secondary Storage
Handled by software called a file system
Areas on secondary storage medium (historically) known as sectors and cylinders
Files stored in one or more (consecutive if possible) sectors
Record of first filename, first sector, etc. kept in a file catalogue/index/directory

10. Computers and Changing the World
First changes: “automatic” calculation
replacement of clerical staff involved in manual calculations
Doing business became increasingly digital (electronic file transfer, document exchange)
Clever “apps” and small computers enabled computers to be used at home
Internet & world wide web…

11. A view of the future from 1968… (!)
First Hollywood film to incorporate an “intelligent” computer, called HAL
HAL had a voice… the actor died this week 
Examples of HAL in action:
controlling a spacecraft
trying to control the astronauts
being turned off…
Very clever “twist” after HAL switched off!!! Watch the film if still interested… 

12. HAL’s “impossible” choice… and his solution
The official explanation was that HAL was given two conflicting orders ("Don't reveal the true nature of the mission to the crew" and "When you get to Jupiter, play the tape that gives the crew their true mission briefing") and was unable to resolve the conflict. An actual human would have realised that the second order would supersede the first one and there'd be no problem, but for all his sophistication, HAL is not human and is designed and built specifically to carry out all orders given to him. The result was that as they approached Jupiter he began to suffer the AI equivalent of a nervous break-down. He either starts to become paranoid or is trying to lead the crew to realise that there is something they don't know in the hopes that they find it out for themselves which would render the first order moot (that conversation where HAL points out the odd aspects of the mission could be evidence for either), then he starts getting increasingly erratic (predicting errors and failures that don't happen), until finally he works out a solution that allows him to fulfil both orders. If the crew are dead, he can play the mission briefing without having to reveal the true nature of the mission to them. It's a wonderfully pragmatic solution in its way, the only problem was he underestimated the resourcefulness and determination for self-preservation of Dave Bowman. As for the final scene, I suspect that this is final proof that HAL really does have emotions and is genuinely afraid. Dave, for his part, appears to start to feel genuine guilt and disgust over what he's doing as he shuts HAL down, he fully realises that he's basically lobotomising a sentient being to death. Ref: PassiveSmoking, 2015, comment in accessed 12/9/18