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The Processors
In 1978 Intel released the 8086 processor.
It had a 16 bit data bus, and a speed of approximately 4.77MHz.
In 1979 they released the 8088. It was an experimental
time for Personal Computers and most of the hardware available
was 8 bit hardware. Intel reduced the data bus in the 8088 to
8 bits, but other than that it was exactly the same as the 8086.
It was capable of addressing 1 Mb of memory. For some reason,
this was IBM's choice of processor for its first PC. Their choice
for an operating system was DOS. In a very short time, there
were millions of these computers sold and DOS became the recognized
operating system for the personal home computer.
The 80286
Even as IBM's Personal Computer was hitting
the markets, Intel was developing a new processor, the 80286.
It ran at speeds from 6 MHz to 20 MHz with a 16 bit data bus.
It's 16 bit memory bus allowed it to address up to 16 Mb of
memory. The 80286 was also the first processor targeted towards
multi-tasking. Since the 8086, all programs needed the entire
1 Mb of memory for operating. By introducing another mode of
operation, known as protected mode, the 80286 could protect
ranges of memory from each other so that more than one task
could be accomplished at the same time, without clobbering each
other's memory space. In essence, what it really did was provide
for a program to have a priority level. The operating system
would have the highest priority. If a program with a lower priority
level tried to access memory allocated to a program with a higher
priority level, the processor would refuse to carry out the
instruction. This usually results in an exception error and
a frozen computer. Still, this was a considerable advancement
in microprocessor technology and was incorporated into future
CPU design. Unfortunately, at the time DOS could only access
1Mb of memory so that's what the 80286 was limited to. The 80286
generally didn't come with a math coprocessor, but it had a
socket for an 80287 chip if you wished to make the upgrade.
The 386
The 386 was a powerhouse compared to previous CPUs (they dropped
the first to digits in the name). It had a 32 bit wide data
bus and address bus with the ability to address up to 4 Gb of
memory. It ran at speeds from 16 to 33 MHz with over 275,000
transistors etched into the chip. The motherboards had a slot
for an optional math coprocessor. The power of the chip was
one thing, but what really set it off was the introduction of
virtual x86 mode. Each DOS program was fooled into believing
it had all the available resources allocated to it, that it
was running on its own virtual 8086 machine. Computers could
now operate in three different modes, real mode (the basic 8086
mode), protected mode, and virtual mode. Multitasking had finally
become a reality. And none too soon either. Microsoft had come
out with Windows, its first attempt at cloning the Mac OS, and
the Graphical User Interface (GUI) was becoming a reality for
the PC.
Other manufacturers (Cyrix, AMD, IBM) also
came out with new 386 processors. Up until this third generation
of processors, Intel had shared its technology with other companies
and most of the processors being made were actual clones of
Intel. With the introduction of the 386, they no longer wanted
to share. In fact, up until now, the other manufacturers had
even used the same numbering sequences for naming their CPUs.
Intel tried to copyright the name "386" but the courts decided
it was too hard to protect.
Intel later came out with another model of
the 386. The only difference was it's 16 bit address bus, as
opposed to the 32 bit original. The cost difference was still
significant and it was offered as an entry level model. They
renamed the original, calling it the 386DX. The new 16 bit version
was named the 386SX. There were, of course, coprocessors available,
the 80387 and the 80387SX.
The 486
The fourth generation of Intel's processors (the 486) was aimed
at improving the performance of what they had. They maintained
the 32 bit address and data bus, and the speed of the system
bus remained at 25 and 33 MHz. There were still 3 operating
modes, real mode, protected mode and virtual mode.
A math coprocessor was nothing new, but with
the 486, Intel had integrated it right into the CPU chip without
requiring an external bus or socket. Another thing they decided
to incorporate into the chip was a small amount of very fast
SRAM (8K) for an internal cache. Up to this point, cache installation
and support had been left up to the motherboard manufacturers.
Just having this small amount of internal (L1) cache alone,
without having to travel the system bus for access, would speed
things up! But Intel learned that by "pipelining"
the information directly to areas of the CPU that dealt with
it, the processor could be working on more than one instruction
at a time. This could allow the 486 to process up to an entire
instruction in a single clock cycle.
With Windows' GUI and the 'user friendly' operating
system (and lots of creative and aggressive advertising), there
seemed to be a mass attack on the markets for home PCs. The
graphical user interface was obviously the future of the home
PC. Computers now had better graphics, better games, a wider
variety of application programs. Number crunching was becoming
a huge part of the computer's work . And yet, when the competitors'
486 processors came out, there was no internal math coprocessor.
Without this added manufacturing cost, these machines could
sell considerably cheaper. The general public didn't realize
the difference. They saw a less expensive 486 and bought it.
The only problem was, that at the time, millions were buying.
Intel recognized the market and rushed to capitalize on it.
They actually disabled the math coprocessor on some of their
CPUs and introduced the 486SX at a cheaper price than the 486DX.
Later development of the chip allowed for dissociation
from the system clock. An internal multiplier inside the CPU
could increased the internal operating speed of the processor
by 2X and 3X. The new versions were named the 486DX2 and the
486DX4 (although it was called the DX4, the internal operating
speed was only increased by 3X). Now there was a whole family
of fourth generation CPUs from Intel. With system bus speeds
of 25 and 33 MHz, the processors ran at 25, 33, 50, 66, 75,
and 100 MHz.
Previously, processors required 5 Vdc. With
the introduction of the 486DX4, voltage was reduced to 3.3 Vdc.
Early upgrades required a voltage regulator between the chip
and the socket. With the DX2, and especially the DX4, overheating
was becoming a problem. A heatsink and fan, attached to the
top of the processor, was required for reliable operation.
continued...
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