Transcript Computer Structures: Lecture 1 Summary

Computer Structures: Lecture 1 Summary
•
Aims of the unit
– To provide foundations for a deep understanding of and skills in handling,
‘computer systems’ (including embedded systems).
• Systems are collections of interacting elements, which together have functions and other
properties which are greater than the sum of the parts.
• Embedded systems are computer systems whose purpose is NOT computation.
– To develop an engineering view, not a superficial view of things
• by studying an essential model (abstraction) of computers/computer systems.
•
Understanding thing X, for engineers at least, by answering the WWCH
(pronounced ‘wuch’) questions.
– Always check your understanding of anything by asking yourself the 4 WWCH
questions.
– What? First define carefully what X really is. You’d be surprised how many
people brag on about something when they really don’t even know what it is - “my
car’s got real time ABS brakes”. If you can’t answer the what question, you can’t
even start to understand X. You can start with a dictionary, if nothing else.
– Why? Is thing X interesting, relevant or important. You need to know this,
otherwise you might be wasting your time on it. It may not be immediately
obvious, so some research and/or questioning others may be needed. You should be
able to answer the why question about anything you do!
Computer Structures: Lecture 1 Summary
– Context? You should be able to figure out how X fits in with the rest of the world.
This will often include social, political and commercial aspects of X. In fact these
dimensions might be more important than any purely technical aspects of X. This
is closely related to the why? question, of course.
– How? Does X work, technically. This is the detail. Depending on the
circumstances, you might need lots of detail here, or a little, or none! Science and
maths knowledge is need to answer the How question.
•
The first of the four WWCH questions is essential, the second pretty much
essential, the last two depend on how deep your understanding of x is going to
be.
What is a computer?
•
•
Box with ….? This is a descriptive answer, not very good for this question
– Descriptive answers to the what question could be OK in other cases, e.g.
what is a triangle.
Functional answer. A digital electronic machine which transforms
information (input) into more useful information (output), so we have:
Input
Computer
Output
3,4
Computer
7
Computer
Weather forecast
Weather data * 1000000
– so the essential model needs input and output mechanisms
– for most computers, they also need a program and some storage (memory)
A mechanical calculator – no program, no storage
A mechanical computer (Babbage) , with ‘mechanical’ program & storage.
(Copy in the Science Museum).
An early electronic computer (~1960), with an electronically stored
program and memory using valves
A early standard working mainframe computer, as might be found in a
bank/commercial company, ~1975. Used transistors and magnetic disks.
Altair, the first Microcomputer – using the Intel 8080, 1975
•
Altair A very bright, variable, double star in the
constellation Aquila, approximately 15.7 light-years
from Earth.
[Arabic an-nasr at-tâ'ir : an-nasr, the eagle (al, the +
nasr, eagle) + at-tâ'ir (al, the + tâ'ir, flying).]
the first popular home computer kit.
•
•
1975 - Altair 8800
The January edition of Popular Electronics featured
the Altair 8800 computer kit, based on Intel's 8080
microprocessor, on its cover. Within weeks of the
computer's debut, customers inundated the
manufacturing company, MITS, with orders. Bill
Gates and Paul Allen licensed BASIC as the software
language for the Altair. Ed Roberts invented the 8800
-- which sold for $297, or $395 with a case -- and
coined the term "personal computer." The machine
came with 256 bytes of memory (expandable to 64K)
and an open 100-line bus structure that evolved into
the S-100 standard. In 1977, MITS sold out to Pertec,
which continued producing Altairs through 1978.
•
ALTAIR- [From a destination in the Romulan neutral
zone in the classic _Star Trek_ episode "Balance of
Terror."]
The film _Forbidden Planet_ is set on the fourth
planet of the Altair system.
•
A Pentium 4 chip , 2004, a successor to the Altair’s 8080, and now
forming the basis of many of the modern desktop and networked home and
commercial computers we all rely on.
The Earth Simulator supercomputer, Tokyo, 2004. We still
need the big beasts!
Computers are not intelligent
•
•
Can only follow the logic of their electronics, or their programs
They don’t do things.
– i.e. they don’t drive cars, make mobile phone calls, or cook dinners.
– but they can output the information (e.g. amount of fuel needed, the phone number
or the number of minutes to cook a casserole) needed to control other devices (fuel
injector, dialling module, cooker heater) which actually do do the work.
•
Designing good programs is hard, because:
– the ways a computer can transform basic information are very simple (electronic
circuits can just about add, subtract and move binary information from one place to
another), so we need lots of instructions working together to do even the simplest
task (think about multiplication or division).
– The world is a complex place and needs computer programs to handle all the big
problems that would take humans for ever to do, or couldn’t do at all.
•
But despite all this, computers are really useful!
– Because they can do things really fast and store vast amounts of information (what
is the latest price to store a bit?)
– Quantum computers are coming along!
•
The human brain probably works differently to an electronic computer
– but we can mimic it, with Neural Networks.
Information (WWCH)
•
What? The precise answer is in Information Theory, but informally,
information
– is what provides unambiguous, structured, detail about things/processes.
• ‘A triangle is a plane figure formed by connecting three separate points with straight
lines.’
• BMW design documents.
• DNA molecule.
– makes order out of randomness
• a human being from a ‘soup’ of molecules.
• a recipe makes a meal from a pile of ingredients.
– can be ‘hard’ or ‘soft’(e.g. this triangle is a right angled triangle or this triangle
looks good’) Engineers work with hard information, soft information needs
interpretation and is subject to opinion.
– Protocols and standards are often needed to clarify information about something
(e.g. “Sunday is the name of the 7th day of the week”, sounds like hard
information, but only if we all agree on a protocol that the day count starts with
Monday as day 1. This is not true in all cultures.
Information
•
•
Why? Generally: Communication and Culture depends on it.
Science:
– The world seems to work in an ordered/structured way: the laws of nature are the
information which describe this order.
– Information and energy are connected, directing the flow of time and the evolution
of the universe! - this is all about thermodynamics. It is also why fast computers
get hot.
•
Engineering: Information allows us to:
– design new things.
– structure the process of their creation, manufacture, development and maintenance.
– control things happening in the real world.
•
How?
– Language, written, spoken (syntax and semantics). As old as mankind.
– Drawings and diagrams. As old as mankind.
– Mathematics records precise, hard information about numbers and anything that
can be translated into numbers. Old, but not quite so old, as mankind.
• Can always be translated into binary 0’s and 1’s and so can be handled by digital
electronic machines.
• was the original reason for developing computers (to solve problems with numbers).
0’s and 1’s
•
•
•
Are called bits.
Can be electronically stored/moved as on/off or high/low - the two different
states possible in a digital electronic machine. Was also the basis of
mechanical semaphores.
Binary 0’s and 1’s (bits) are just codes,
– which provide the simplest (but giving the most headaches to humans) way of
writing down numbers.
– Which can be used for a million other things we might want to have codes for, in
order to store hard information about them;
•
•
•
•
•
•
Information does not have to be coded in 0’s and 1’s
–
–
–
–
•
music
Images, digital TV.
characters of the alphabets of the world (unicode)
colours
things to buy (bar codes) and more ………………..
but it does in a conventional digital electronic machine.
an optical computer could work with 5 different states.
your DNA molecule stores information using 4 different sub-molecules.
a quantum computer might have millions of basic states.
Hexadecimal and octal are just bigger codes to avoid writing down all those
0’s and 1’s. Computers don’t work in hexadecimal or octal