Anatomy of a Computer

RAM, ROM, CPU, etc. [This material can be found in

Chapt. 3 of Discovering Computers 2000 (Shelly, Cashman and Vermaat).]

A chip off the old block

Millions of transistors are connected into what is called an integrated circuit or chip

The most important chip in a computer is the microprocessor

The microprocessor houses the Central Processing Unit (CPU), the “brain” of the computer

Ex. The Pentium II is a microprocessor

How many?

Word size and bus width Computing means moving bits

around, so an important question is how many bits can be handled at one time

analogy: two-lane, four-lane or eight-lane highway

How fast?

Each of the computer’s manipulations (instructions) begins a “tick” of the clock

So the faster the clock ticks, the faster the computer

Clock speed: a measure of how fast the computer is, given in MHz (megahertz - millions of cycles per second)

Middle number written on LaSalle’s computers

How fast? (Cont.)

Sometimes one instruction can be started before the previous one was complete

Like have a batter on deckSo another measure of speed is usefulInstructions per second, another

measure of speed, is measured in MIPS (millions of instructions per second)

The mother of all circuit boards

chips and other things are connected together on what is called a circuit board

the mother board, a.k.a. the system board, holds the main components of the computer CPU clock connectors expansion slots, ETC.

The fan and the sink

The chips, especially the microprocessor can get hot

heat sink: the strangely shaped metal or ceramic structure sitting on the processor that serves to draw away the heat

there’s also a little fan near the processor; that’s often what you hear on old computers

A link to the outside world

The process of putting information into or getting information out of a computer is called interfacing or input/output (IO)

ports are sockets, typically in the back of a computer, where one plugs in the cable connecting the computer to the IO devices

Two types

serial data sent one bit at a time for modems and some printers cable can be very long ex. MIDI, USB

parallel data sent eight bits at a time limit on length of cable ex. SCSI

SCSI port

Small computer system interfacepronounced “scuzzy”allows more than one device to be

connected to a single portdaisy chain: getting the output for a

second output device from the first (rather than directly from the computer), the output for a third can come from the second and so on

A connector in every port

Ports have connectors, as do cablesconnectors come in two varieties

male: have pins sticking out female: have holes to receive pins

Analog to Digital

Any measurement that can be converted to an electronic signal (voltage or current) can be directly fed into a computer

the original data is often continuous (analog) and must be converted into digital form

This signal can be fed in through a port (typically the RS-232 port) so long as the appropriate software is installed

In the cards

Expansion Slot: A socket designed to hold the circuit board for the device, such as a sound or video card, that adds capability to the computer system

Adapter cards: additional circuitry and chips that extend your PC’s capabilities allowing you to customize it

Some types of cards

video or graphics card: enhances computer’s ability to convert output into video and send it to the monitor

Sound card: improves your computer’s sound capabilities, be it input (microphone) or output (speakers)

internal modem: allows computer to connect to networks via phone lines and such

Plug and play

refers to computer’s capability to figure out what to do when new expansion cards and devices are added

this way the user does not have to know how to “configure” the system

Memories

Saving information we have entered (e.g. onto floppies) is referred to as “storage;” it is long term and slow by computer standards (storage memory)

Before we save the data, it is in the computer’s memory, i.e. in memory chips, which hold the information temporarily

Memory also holds the instructions a computer needs to operate

ROM

Read Only Memory This memory is loaded up by the

manufacturer (some is programmable)

contains low-level instructions for the computer

Not lost when the computer is turned off“nonvolatile” memory“stored program concept”

RAM

Random Access MemoryThe memory the user uses The programs one loads and the

data one enters are here Lost when the computer is turned off “volatile” memoryrandom?

Random Vs. Sequential

A cassette tape is sequential access; you have to go through song one and two to get to song three

A CD is random access; you can jump directly to song three

Some Types of RAM

Dynamic RAM (D-RAM): dynamic means changing, which for memory is not necessarily a good thing, so dynamic memory must be continually refreshed Synchronous DRAM — when the memory update

and clock are better coordinated (“in synch”)Static RAM (SRAM) doesn’t need constant

refreshing, is faster but more expensive than dynamic

Cache

pronounced “cash”it’s an area of high-speed memory (often

SRAM)Instead of looking through the slower

RAM, data is looked for here first, a speedy intermediary

You often encounter the term while surfing the web; data from a web site can be stored in a cache

Buffer and Clipboard

Buffer: where data coming in (from input devices) or going out (to output devices) is stored until the transaction is complete

Clipboard: Memory location where data is placed during an application such as word processing (cutting or copying puts data on the clipboard); it is also used to transfer data from one application to another (e.g. from Excel to Word)