Anatomy of a Computer

RAM, ROM, CPU, etc.Chapter 4 in Computing Essentials (O’Leary and O’Leary)

A chip off the old block

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

Chips are made from silicon (a semiconductor, a material halfway between a conductor and an insulator)

“Silicon valley” is a nickname for the region south of San Francisco that contains an unusually high concentration of computer companies.

CPU

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 III is a microprocessor

Extending the brain analogy

Similar to dividing the brain into Brain stem Forebrain

We divide the CPU into Control Unit Arithmetic Logic Unit (ALU)

How good is your computer?

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

Word size: how many bits are handled at a time (8, 16, 32, 64) by memory or the processor

Bus size: how many bits can move around at once analogy: two-lane, four-lane or eight-lane highway

Bus speed: how fast they move

How fast is it?

Each of the computer’s manipulations (instructions) begins with 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) There are gigahertz machines now

Middle number written on LaSalle’s computers

Speed II

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

Like have a batter on deckSo another measure of speed is useful instructions per second, given in MIPS

(millions of instructions per second) (considered by some to be a misleading

measure of speed)

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

If you can’t stand the heat

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 whirring away 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 Newer computers have a port in

the front for convenience

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 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 (“stored program concept”)

Reading and Writing

The basic actions involving memory are WRITING: putting information into

memory READING: getting information from

memoryThe rest of the time memory just

holds onto information

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

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” memoryWhy is it called random?

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 (DRAM): dynamic means changing, which for memory is not necessarily a good thing, so dynamic memory must be continually refreshed Synchronous DRAM: when the memory and a

clock work together to send blocks of data more efficiently

Static RAM (SRAM): doesn’t need constant refreshing, is faster but more expensive than dynamic

Cache

pronounced “cash”The computer puts information it

anticipates (guesses) you will use soon in a place which is accessed more quickly

A correct guess is called “a cache hit”, an incorrect guess “a cache miss”

Caching improves speed

Some kinds of cache

Memory cache: put information from DRAM into SRAM (high-speed memory) L1 on the chip with the microprocessor L2 on a different chip

Disk cache: put information from storage (floppy or hard drive) into memory

Browser cache: put information from internet into hard drive

Buffer

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

Printer buffer: when you send something to print, it may not print right away, but instead sit in the printer buffer awhile There is usually an icon on the task bar

indicating that you have something in the printer buffer

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)