Inside the CPU COSC-100 (Elements of Computer Science) Prof. Juola

What’s a computer? Information-processing device Primary function : math, decisions Normally “digital” (vs. analog) 1:38 pm

Computers : A history 3000 BC -- digital counting device (abacus) 16th c. -- Napier’s bones 19th c. -- Jacquard’s (programmable) loom Babbage’s Analytic Engine WWII, programmable coding and decoding machines (Colossus)

Computers: A history (cont.) Programmable computers ENIAC 10 feet tall, 10,000 square feet footprint, 150kW of power, and 18,000 vacuum tubes First program “bug” Moth found in computer Harvard Von Neumann defines “computer”

Computers: A history (cont.) First transistor (no more tubes!) Begins “second generation” computers First programming language First integrated circuit, Begins “third generation” computers VLSI microprocessor Computer-on-a-chip Begins “fourth generation” computers

Computers: A recent history Intel builds 4004, eventually to become the Pentium (IV) Microsoft founded IBM produces IBM-PC (Personal Computer) Apple Macintosh Change in hardware since then mostly incremental

Software : A history : Institutional computing Banks, large corporations, scientific problems : Personal computing Document processing, data storage, calculations today : Interpersonal computing Primarily networking ; , web, IM, gaming

Computing issues Computers are algorithmic; they only do what you tell them to do. Limited by validity of data : GIGO principle Primarily an enabling tool, but enabling of what?

Structure of CPU CPU most salient part of computer E.g. “Intel Pentium 4 Processor at 3.4GHz with 800 MHz front-end bus” Describes type of computer (Pentium 4), and how fast it does stuff (3.4 billion clock ticks/second)

Electronically Speaking Basic computer design hinges on electronic switch (valve?) controlling current Current is either flowing or not. Fundamental representation : flowing/not becomes a yes/no or a 1/0 “binary” representation. All quantities in computers represented by binary quantities

Representations Numbers : becomes 23 2^4 + 2^2 + 2^1 + 2^ = 23 Letters : becomes ‘A’ American Standard Code for Information Interchange (ASCII) Code : becomes “add integers” Programs (compilers) to convert from human languages to “machine language”

Electrical manipulations Binary patterns manipulated through electronic circuitry

Storage More circuitry creates self-powering (stable) circuit for temporary data storage

CPU Structure Several sub-components Arithmetic-Logical Unit -- does math/logic Bus Unit -- talks to rest of computer Prefetch/Decode Units -- load/figure out next instruction Control Unit -- executes instructions, controls rest of CPU Cache memory -- high-speed local memory for scratch-pad style storage

Terminology Bit -- one yes/no pattern Byte -- 8 yes/no patterns, grouped Word -- several bytes, grouped for easy manipulation 8-bit computer : microcomputer 16-bit computer : minicomputer 32-bit computer : mainframe 64-bit computer : ?? 128-bit computer : supercomputer

More terminology Kilo : either 1000 or 1024 (2^10) Mega : one million Giga : one billion Tera : one trillion Example : 1 GHz is one billion Hertz, and a 256 MB pen-drive stores 256 million bytes

Why different CPUs? Different capacities : bigger word size means more expensive, but also more powerful. Why buy more than you need? Incompatible designs. Different machines (e.g. PowerPC vs. Pentium) have different machine codes, different architectures Different philosophies : RISC vs. CISC

Virtual machines “The CPU that isn’t.” Virtual CPU is software to interpret patterns for another machine. E.g. your Mac can run PC software. Java Virtual Machine exists nowhere but in software. As software, built into every web browser, so Java programs run everywhere the Web does.

Moore’s Law Eniac had 18,000 tubes Pentium 4 has 55 million transistors Gordon Moore (1965) observed : The number of transistors that can be put on a chip doubles every eighteen months The cost of a given amount of computing power halves every 18 months The cost to develop a new chip doubles every 18 months.

Why so important? Primary factor : transistor size Smaller transistor takes up less space … but also draws less power operates faster costs less to fabricate (but more to design) Unknown how long Moore’s law will continue to be true.

Programs get bigger Demand for programs is getting larger PDP-11 text processor (troff) used less than 64K of memory. Compare to MS-Word Game design often pushes limits of both computer speed and memory capacity. How to make computers faster?

Multiprogramming Multiple CPUs per “computer,” all cooperating Extreme example : CM-2 Connection Machine had 65,536 CPUs. Alternatively, use networked computers

The future Transistor density may hit fundamental limitations (can’t build a transistor smaller than an atom). Faster substances (GaAs?) DNA computing in experimental stage “Quantum computing” a possibility, but will require fundamental re-think of how computers work.

The future (cont.) Smaller computers mean more uses (e.g. PDA’s, MP3 players) “Ubiquitous computing” aims to put Star Trek style computers everywhere for simple tasks. Computer assist for many tasks we can’t even imagine today.