Machine Architecture
An Introduction
to
Computer Components
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Major Computer Components
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Central Processing Unit (CPU)
Bus
Main Memory (RAM)
Secondary Storage
I / O Devices
Starting the computer
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CPU
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Central Processing Unit
The Brain
Controls all other computer functions
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The Bus
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Computer components are connected
by a bus
A bus is a group of parallel wires that
carry control signals and data between
components
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Main Memory
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Main memory is made up of capacitors
If the capacitor is charged, then its state
is said to be 1 or ON.
We could also say the the bit is set.
If the capacitor does not have a charge,
then its state is 0 or OFF.
We could also say that the bit is reset
or cleared.
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Size of Capacitors
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Has decreased dramatically over the last 20
years.
Now we can fit several million capacitors on
a chip the size of a dime.
As this technology becomes older, we can
expect the price of memory to decrease. Is
it already decreasing ? ABSOLUTELY !
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Memory, the continuing saga
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Memory is divided into cells, where
each cell contains 8 bits. Remember
that 8 bits is called a byte.
Each of these cells is numbered.
The number associated with a cell is
known as its address.
Volatile storage
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Reading & Writing
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In addition to the circuitry that holds the
bits, there are other circuits that allow
other components to
o Get the value of the data held at a
particular address - known as a READ.
o OR store data at that address - known as a
WRITE.
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Memory Access
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All addresses in memory can be
accessed in the same amount of time.
We DO NOT have to start at address 0
and read everything until we get to the
address we really want.
We can go directly to the address we
want and access the data.
That is why we call Main Memory RAM
- Random Access Memory
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Secondary Storage
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Disks -- floppy, hard, removable
Tapes (sequential access)
CDs
Stores files
o programs
o data files (binary, text)
o directory structure
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Persistent storage
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I/O
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I/O is handled by peripheral devices.
A peripheral device is some machine that is
not an integral part of the computer.
Examples:
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monitor
keyboard
mouse
disk drive
printer
scanner
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Media
• Many I/O devices work in conjunction with media
• A medium holds information (programs, data, text
files)
• Examples:
• floppy disk (not the drive itself)
• hard disk (not the drive itself)
• magnetic tape (not the drive itself)
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Bits, Bytes, and Words
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A byte is 8 bits
A word is 32 bits or 4 bytes
Long word = 8 bytes = 64 bits
Quad word = 16 bytes = 128 bits
Programming languages use these standard
number of bits when organizing data storage
and access.
What do you call 4 bits ??
(hint: it is a small byte)
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Booting the Computer
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The term boot comes from the
expression pulling yourself up by your
bootstraps.
It refers to the computer’s start-up
procedure.
When the computer is first turned on, it
reads start-up instructions found in the
ROM chips.
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Booting the Computer (continued)
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These instructions cause the computer to do a
series of tests. Each of the components is tested.
The last thing that happens during boot is that the
operating system is loaded from the hard disk into
RAM.
The computer cannot do anything until the
operating system is loaded, because the
operating system manages all of the basic
functions of the computer.
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