Text 6
The floppy driver you see here works with three in a half into floppy
disks. They are the types most often used to carry new programs, save data, or
to move file from one PC to another. The part of the disk we see is actually
just a hard plastic shell. The working disk which is inside, is protected by
sliding metal shelter. The stain in a disk called the cookie, is coded not with
chocolate chips, but with a very thin layer of magnetic material.
When you slip the disk into your floppy driver a system of labors
pushes back the metal shelter. The labors also pinch to read-write heads
closer, so they almost touch the cookie. A mode of the base of the drivers
spins the cookie, based on the commands from your PC. The PC also signals
another mode and move the read-write head back for over the surface on the
disk. So they can read or write data.
Before your PC writes data, your driver first checks the right
protector over the corner of the floppy disk. If it’s open light from a tiny
diode shines through, it strikes of a
diode on a other side. This diode then sends to your PC:
“Don’t write
on this disk”. But its tab is closed no light gets through and the PC knows it
is OK; you write data.
Text 5.
Patterns of pits and lands are laid out along a continuous spiral. As
the disk turns, a precise motor keeps the laser beam in place on the path. When
the laser beam hits a pit, the light is scattered. But where it hits a land the
beam is reflected straight back along its original path. The light enters the
prism again. But this time it is reflected at a 90 degree angle and strikes a
device called a diode. The diode creates an electric pulse each time the light
hits it. So when the laser hits a pit no light bounces back. When it strikes a
land the diode sees the reflection and sends a pulse. These blanks and pulses
are sent to the computer, which interprets them as a pattern of zeros and ones.
In other words, into binary code.
Text 4.
How can a CD-ROM can hold so much more than a conventional disk? The CD
driver reads data with a beam of light so narrow that the information can be
squeezed together much tighter. You see, a laser diode creates this
concentrated beam of light. The light travels through a prism, then through a
lens and magnetic coil that focus the beam even more.
On the under side of the compact disk itself are millions of tiny bumps
called pits. That's right, the bumps are called pits. The same surface has
smooth areas called "lands". These pits and "lands" are
translated into the binary language of bits and bytes used by the computer.
Text 3.
There are many types of buses used in PCs today. How faster PC performs
depends on the type of bus it uses.
The original IBM PC used an 8-bit bus to transmit data along parallel
data lines like these. The modern 16-bit bus, also called an ISO bus,
transports data over 16 lines. To remain compatible, it can also accept older
8-bit adapter cards. The more advanced ESO bus doubles the numbers of lines
again to 32. 8 and 16-bit cards fit into the ESO slots far enough to only
contact the first row of 16 connectors. On the other hand a true ESO board
connects with all 32 contacts.
The local bus overcomes a major problem with all the previous buses,
namely slow speed. The original PC’s bus ran at 8MHz, but now modern processors
can run at 66MHz or more. To accommodate these high speeds the local bus can
carry 32-bits of data at a time at the speed of the clock chip. If your local
downtown bus suddenly went 10 times faster, you’d definitely sit up and take a
notice. But for a modern PC bus it’s just another cruise down Main Street.
Text 2.
How do all the different components of your computer communicate with
each other? They use special electronic pathways called a bus. Just like a
passenger bus that can transport large amount of people, the computer’s bus can
carry a great deal of information. The bus allows the computer’s standard
peripherals such as the keyboard, monitor, to talk to each other and other
parts of PC.
They are made out of numerous
electronic pathways called the circuit lines along which power and data travel.
The original IBM PC’s 8-bit bus has 62 lines, 8 of which transmit power to the
adapter card. Another 8 to 32 lines carry data to various components such as
memory chips or display. The next 20 lines are called address lines. They carry
a coded road map to where the information is traveling. Each adapter card has
unique destination or address on the route of the bus. The remainders of the
bus’s lines carry commands for the standard computer operation such as reading
or writing data. Every component plugged into the bus is constantly looking for
signals coming down the command line.
When a signal to write data appears only the input/output devices
recognize the command, other device such as the memory circuits do not. Alerted
by the right command the IO devices check the address lines. If the code
matches its address, the adapter accepts the data and follows the new command.
Otherwise the adapter simply ignores the command.
Text 1.
We have been
looking at an Intel three eight six processor, have relatively weakling these
days.
The more
powerful Intel 486 processor is similar to the 386 except that it has two other
components.One is a small eight kilobyte memory cache. Its purpose is to scroll
away little data code so that they can
be processed as soon is the CPU is ready. A 486 DX processor also has a numeric
processor unit built into it, to speed things even faster.
The newest Intel
processor, the Pentium, has two memory caches, one for code, one for data. And
it has two execution units so that two separate software instructions can be
processed at the same time. These features go a long way to make in the Pentium the fastest chip
available for the PC.
