COMP1321 Digital Infrastructures Richard Henson November 2017

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

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!

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

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

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)

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…

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)

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

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…

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  https://www.youtube.com/watch?v=KztuulxC8H4 Examples of HAL in action: controlling a spacecraft https://www.youtube.com/watch?v=BDha7nj4s10 trying to control the astronauts https://www.youtube.com/watch?v=ARJ8cAGm6JE being turned off… https://www.youtube.com/watch?v=UgkyrW2NiwM&t=135s Very clever “twist” after HAL switched off!!! Watch the film if still interested… 

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 https://www.youtube.com/watch?v=boaf_U3-Q0E accessed 12/9/18