How They Really Work

Osher Lifelong Learning Institute
University of Illinois, Urbana-Champaign

Scott Badman, Instructor

Hardware

Disassembling a desktop computer

Computers are generally safe, even when plugged in.

At most 12 volts, usually 5 or 3.3 volts.

Only exceptions:

The power supply (don't disassemble)

Lasers in optical disk drives (laser could hurt your eyes, but it would have to plugged in while disassembled)

Old tube-type monitors (never, ever take the back cover off, even if unplugged - the flyback transformer can kill you even after days without power).

Power supply

Don't disassemble

Generally: a different plug for each voltage and wattage to prevent burning out equipment, but the same plug for all the different types of equipment that can use it.

Storage drives

Magnetic Hard Drives

Disassembled hard drive.

Stores data as incredibly tiny spots of magnetism on metallic coating.

Platter, Read/Write Head, Actuator motor

The control board is actually a special purpose computer with all the components we will see later

Read / Write times: in milliseconds (thousandths of a second).

Extremely cheap: pennies per gigabyte (one billion units of binary data).

Optical Hard Drives

All work the same way, reading pits pressed or burned into a layer made of metal or dye.

3 generations: CD, DVD, BluRay

Distinguished by the wavelength of the laser used.

The pits are about 1 1/2 the size of the wavelength of the laser light.

All backward compatible (example of core concept)

Read / Write Times: in milliseconds, similar to magnetic drives

Cheap: dollars per gigabyte.

Biggest advantage: the disks are removable for storage and exchange.

Solid State Drives.

Flash memory - uses same technology as transistor based memory chips, but will retain data when the power is off.

Read / Write times: Fractions of a millisecond. Faster than magnetic or optical because does not have to wait for disk to turn to the right position - but performance degrades over time, and failures are usually total

Moderate cost: dollars per gigabyte, have only become economical recently

Common characteristics of all internal drives:

Compatible connectors whenever possible, only a few in general use

Compatible form factors (physical dimensions and attachment techniques)

Compatible communication protocols, how data flows between devices.

Illustrates core concepts:

Importance of standards to allow different components to work together

Maintaining compatibility, especially backwards compatibility

Isolation of complexity

Other types of drives:

Flash Drives (Thumb Drives, Jump Drives)

Same technology as Solid State Drives, at about the same performance and cost per gigabyte

Big advantage: easily removable

Logical Drives and Virtual Drives

Part of a drive or other memory that can appear as a separate drive to a computer system

Example: A file that is formated like a CD Drive. Such a file usually has the .iso extension in its name, it can be encrypted and e-mailed just like any other file.

We will see Logical Drives when we talk about the Windows Operating System.

Main Memory

Extremely Fast: Read/Write in nanoseconds (billionths of a second)

Moderate cost: Tens of Dollars per Gigabyte

Loses all data if power is shut off

Being replaced by flash memory in lots of devices where internal speed is not as important: such as cell phones and tablet computers.

One of the core components in the definition of a computer -- all computers must have some form of memory.

Graphics Cards

Only needed if you want high end graphics for work or games

They have become their own specialized computer with all the same components we will see on the motherboard.

Specialized electronics to support the type of mathematics needed by Graphics

Motherboard

There are about three common sizes, with lots of interchangeability

Speed - incredibly fast, measured in nanoseconds (billionths of a second)

Grace Hopper's "nanosecond" - the distance light travels in one nanosecond, about 1 foot

The computation: 300,000,000 meters per second times (1/ 1,000,000,000 seconds) or 0.3 meters or about 1 foot

Electricity travels down a wire at about 2/3 to 9/10 the speed of light, or about 8 to 10 inches per nanosecond.

The motherboard has to be designed very carefully to operate at those speeds.

The clock crystal on the motherboard. Sometimes there is also a secondary clock crystal.

The clock sends out pulses that coordinates all the other electronics so it works together.

Printed circuit board connections

Buses - parallel connections

Width of bus (how many parallel lines) very important - determines speed

Normal current widths - 32 and 64 (also 128 and 256 in high end video cards) (notice these are all powers of 2)

Early PC's from the 80's and mainframes from the 50's had 8 and 16 bus widths

Problem with all the pulses arriving at the same time. Can only be for short distances (measured in inches)

Serial lines - data travels one pulse at a time

Previously much slower than parallel, but is catching up in some situations

No problem with all the pulses arriving at the same time -- can travel far distances

Central Processing Unit

The most important logic and arithmetic processing

Must be highly compact for speed. Operates at a half or third of a nanosecond

Size of your thumbnail - everything else is packaging and heat control

Uses about 30 to 120 Watts, and puts out as much heat as an old incandescent light bulb

Chipset

Early computers did not have the standardized chipsets of current computers.

North Bridge Chip - primarily controls data flow from the CPU to the main memory and other extremely fast devices

South Bridge Chip - controls data flow from North Bridge to slower I/O devices, such as disk drives and networks

BIOS (Basic Input Output System)

A "Firmware" program that is permanently burned into a chip installed on the motherboard

Boots the computer and does the most basic input and output when the computer is starting

We will talk about it in the "Windows Operating System" session.

Various internal storage drive, card, and power connectors

Highly standardized - If the connector fits, usually (but not always) the piece of equipment can be made to work on that computer.

Many pins - bus connections for fast speeds

Various external I/O connectors.

Mostly Serial (one pulse at a time, such as the USB port) or analog (varying voltages carry the information, such as audio)

Back Up Battery

Keeps the computer's clock running, and to save the computer configuration information for the BIOS

Case

Has a fan, cooling is very important

Typical computer uses about 200 - 300 watts, and produces the heat of 2 or 3 100W light bulbs

Other Input/Output cards

Other types of Input and Output: Video and Graphics with or without Touch Pad, Network, Sound, Printers, etc.

Almost all Input and Output is now migrated to the motherboard from separate cards attached to the motherboard.

A lot of the specialty input and output, such as MIDI cards for audio production, have migrated to Universal Serial Bus (USB) connections.

The most common separate I/O card now is the Graphics card.

Commonalities:

Almost all have a hardware part, and a firmware program on the card, and a software driver as part or the operating system.

Standardization and interoperability has been generally very good with computer peripherals - even between Apple, PC, and Linux computers.

Commonalities and historical trends:

Everything used to be controlled directly by the CPU (in the 50's and 60's mainframes and 80's PC's).

Every device used to be separate and external, with different hardware, often mechanical.

Over time, more and more hardware migrated to the motherboard.

Over time, more and more of the hardware interfaces became standardized and interchangeable when possible, even between different types and brands of hardware.

Unix was the leader in standardization of Input / Output to different kinds of peripherals -- all Input / Output was just a flow of binary 1's and 0's.

Magnetic disk drives, optical drives, and flash drives all appear to the main computer as the same hardware.

The Universal Serial Bus (USB) port allows a wide variety of hardware to be interchangeable as far as the user is concerned.

Over time, more and more of the functions migrated to controllers, which are really dedicated computers

Controllers communicate with the main computer on the motherboard through protocols.

Control board of disk drive and Cisco router with memory, CPU, I/O chips, and firmware programming.