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 deck
So another measure of speed is useful
Instructions 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 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
(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 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
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 (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)