Transcript Anatomy of a Computer

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 deck
So 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 interface
pronounced “scuzzy”
allows more than one device to be
connected to a single port
daisy 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 cables
connectors 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 memory
The 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 Memory
The memory the user uses
The programs one loads and the data one
enters are here
Lost when the computer is turned off
“volatile” memory
Why 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)