Transcript CMSC 104 - Computer Science and Electrical Engineering

Machine Architecture
An Introduction
to
Computer Components
CMSC 104
1
Major Computer Components
Central Processing Unit (CPU)
 Bus
 Main Memory (RAM)
 Secondary Storage
 I / O Devices
 Starting the computer

CMSC 104
2
Computer Functional Diagram
CMSC 104
3
CPU
Central Processing Unit
 The “brain”
 Controls all other computer functions

CMSC 104
4
CPU (Continued)

Types
o Intel: 4004, 8008, 8080, 8086, 80186,
80286, 80386, 80486, Pentium, Merced, ?
o Motorola: 6800, 6809, 68000, 68020,
68040, 68060, 68080, RISC, ?
o DEC: PDP-8/10/11, VAX, Alpha, ARM, ?
o AMD: K4, K5, K6, K7, ?
o Zilog: Z80, Z800, Z8000 (Still around?)
CMSC 104
5
CPU (Continued)
Just a collection of fast ON/OFF switches
Forty-million transistors in this space (or less)
CMSC 104
6
CPU (Continued)

CMSC 104
Some MainFrame CPUs are limited by
the speed of light.
7
The Buss
Different major components are
connected by the buss.
 A buss is a group of parallel wires (or
circuit-board connections) that carry
control signals and data between
components.

CMSC 104
8
Main Memory
Main memory is made up of two-state
devices.
 Two state devices have just two
possible states (Wow!). An ON/OFF
switch is a two-state device.
 In memory, one state stands for 1, the
other for 0.

CMSC 104
9
Main Memory (Continued)
Memory can hold any type of data that
can be represented by a combination of
two states --- and only those types.
 Examples:
 1 = yes, 0 = no
 01 = Red, 10 = Blue, 11 = Green
 00 = 0, 01 = 1, 10 = 2, 11 = 3

CMSC 104
10
Main Memory (Continued)

CMSC 104
Memory often made up of capacitors
(electron storage devices).
 “Charged” (“full”)
1, ON, SET.
 “Discharged” (“empty”)
0, OFF, RESET, CLEARED
11
Main Memory (Continued)
“The Incredible Shrinking Capacitor”

Technology is constantly improving
o Experience
smarter engineers
o Smarter engineers
smaller devices
o Smaller devices
cheaper systems
o Cheaper systems
more sales
o More sales
more experience
CMSC 104
12
Main Memory (Continued)
“The Incredible Shrinking Capacitor”
Memory chips now routinely contain
128x220 (“128 Meg”) bits.
 “If car-makers built cars the way chipmakers build chips, we’d all drive
Mercedes-Benzs that cost $4.95, got
1000 miles to the gallon, and fit in our
pockets when we got to our
destination.”

CMSC 104
13
Main Memory ((still) Continued)
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 is the cell’s address.
 The address is the, um, ah, er, well the
“address” we use to specify which byte
we want to work with.

CMSC 104
14
Main Memory
“Nepenthe: Elixir of Forgetfulness.”
Main memory is volatile (it goes away
when you turn off the power).
 Capacitors leak
charge goes
away
data is lost.
 “If car-makers … and they would
disappear as soon as we turned off the
engine.”
 There are non-volatile memory systems.

CMSC 104
15
Main Memory
Reading & Writing (for ‘rithmetic)

In addition to the circuitry that holds the
bits, there are other circuits that:
o Get the value of the data held at a
particular address --- READ.
o Store data at particular address --- WRITE.
o Some memory is designed so that it cannot
be written
Read-Only Memory
ROM
o Many types of ROM are non-volatile.
CMSC 104
16
Memory Access
Memory at all addresses can be
accessed in the same amount of time.
 Memory can be accessed in any order,
like cuts on a CD (not “Byte0, Byte1,
Byte3, …, ByteN” like cuts on a tape).
 Access in any order
Random
Access
Random Access Memory
RAM

CMSC 104
17
Secondary Storage

Many Types:
o Disks (Random Access)
o Tapes (Sequential access)

Persistent storage (Stays when the
power goes off)
o Programs
o Data files (binary, text)
o System organization (Directory structure)
CMSC 104
18
I/O
Converts some “real” thing (sound,
movement, electrical signal) into bits.
 Usually done by specialized “add ons”

o Keyboard
o Monitor
o Soundcard

CMSC 104
Sometimes disk and tape drives are
considered I/O devices.
19
Computer/Peripheral Communication
“There be Dragons and Mysteries in these Waters.”

Ports
o Electronic connections through which data
can enter or leave the computer
o Identified by port numbers (like memory
cells are identified by addresses)
o Usually each device (keyboard, soundcard,
network card, modem) with be assigned to
exclusive use of one or more ports
CMSC 104
20
Computer/Peripheral Communication
Doesn’t everyone speak Latin ?

I/O devices normally exchange two
things with the computer
 “Data” --- e.g. bits to and from a
modem --- this is what you want
 “Protocol” --- coordination between
the computer and the device to insure
the data is transmitted correctly --you don’t see it and you don’t want to.
CMSC 104
21
Computer/Peripheral Communication
“No thanks, I peel my own.”

Protocol insures that the device and the
computer “speak the same language.”
 Parity (must there be an even number
of bits per exchange?)
 “Endedness” (some computers
transmit numbers from-left-to-right,
others from-right-to-left)
CMSC 104
22
Computer/Peripheral Communication
“Let’s not both talk at once”

Usually duplex (two-way) rather than
simplex (one-way)
Simplex: mail, TV/Radio broadcast.
o Half-duplex: two-way communication, but
in communication can occur only in one
direction at a time (polite telephone call).
o Full-duplex - allows communication in
both directions at the same time.

CMSC 104
23
Computer/Peripheral Communication
Controllers
Special-purpose “CPUs” designed to
handle I/O
 Free main CPU by taking over comms
tasks.
 Allow more complex I/O, more devices
 So effective that many machines are
designed to use controllers even if only
one device is connected to a port.

CMSC 104
24
Computer/Peripheral Communication
Parallel and Serial Communication
Parallel - All the bits of a pattern are
transferred at the same time, with each
bit being transferred on a separate line.
Requires multi-wire cables. “Gimme
Five!”
 Serial - Transmits one bit at a time.
Slower, but uses a simpler data path.
“Here’s one bit, here’s another bit …”

CMSC 104
25
Bits, Bytes and Words
A bit is a single 1 or 0; a single choice
 A byte is 8 bits

o A word is 16 bits or 2 bytes
o Long word = 4 bytes = 32 bits
o Quad word = 8 bytes = 64 bits
o Programming languages may use these
terms when organizing data

CMSC 104
A <what> is 4 bits?? (It’s a small byte.)
26
More Bits and Bytes
There are 16-, 32-, and 64-bit machines
 All of UMBC Unix systems are 32-bits

CMSC 104
27
Booting the Computer
It refers to the computers start-up
procedure.
 Comes from the expression “pulling
yourself up by your bootstraps”
 Starts with instructions stored in the
ROM chips. (Why: two reasons.)

CMSC 104
28
Booting the Computer (continued)

A typical boot sequence:
o Test critical components (and maybe all
components).
o Turn on and setup critical devices (console,
keyboard, power monitor, operating system
storage media)
o Load operating system (usually from disk)
o Transfer control to operating system.
CMSC 104
29
Booting the Computer (continued)
The Operating System (O/S)

O/S provides fundamental services for
all other tasks:
o data storage
o I/O
o Program execution
O/S is usually stored on disk, but not
always: PalmPilot
 Once O/S is running, computer can be
fully functional.

CMSC 104
30