Machine Architecture
An Introduction
to
Computer Components
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Major Computer Components
Central Processing Unit (CPU)
 Bus
 Main Memory (RAM)
 Secondary Storage
 I / O Devices
 Starting the computer
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CPU
Central Processing Unit
 The Brain
 Controls all other computer functions
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The Bus
As you can see from the diagram, the
computer is made up of different
components, like the CPU and main
memory.
 The components are connected by the
bus
 A bus is a group of parallel wires that
carry control signals and data between
components
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Main Memory
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
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
Memory is divided into cells, where
each cell contains 8 bits. Remember
that 8 bits is called a byte.
 Each of these cells are 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
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
Disks -- floppy, hard, removable
 Tapes (sequential access)
 CDs
 Stores files
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o programs
o data files (binary, text)
o Directory structure
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Persistent storage
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I/O
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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o Monitor
o Keyboard
o Disk Drive
o Printer
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Bits, Bytes and Words
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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More Bits and Bytes
There are 16-, 32-, and 64-bit machines
 All of UMBC Unix systems are 32-bits
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Booting the Computer
The term boot comes from the
expression pulling yourself up by your
bootstraps.
 It refers to the computers 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)
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.
 The computer cannot do anything until the
operating system is loaded, because the
operating system manages all of the basic
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