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                                     3




                                 Processor























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Chapter 3 - Processor


Understanding CPU Generations

     Computer processors, also known as the CPUs (Central Processing Units),
are the heart and soul of every computer.  Without the CPU the computer doesn't
think, and therefore, it doesn't work.  Intel (I know you have seen their ads 
on TV about the "Intel inside" idea) has been supplying IBM and most IBM 
compatible (compatible with IBM's original computer and software design) 
computer makers with CPUs since their beginning.  Therefore, Intel sets the 
standard when it comes to IBM compatible CPUs and that's what I will explain to 
you.

The following chart shows each generation of CPU used in IBM and compatible
computers.  Intel named each generation of its CPU with a number, and often 
these CPU chips are referred to by the last three digits of their number.  For 
example: an 80386 is referred to as a 386.  The 80486 is a 486 and so on.


CPU type       CPU Generation      Typical Speeds
--------       --------------      --------------

8088           First               4.77Mhz
8086           Revised First       4.77Mhz
80286          Second              6Mhz-16Mhz
80386          Third               16Mhz-40Mhz
80486          Fourth              25Mhz-120Mhz
Pentium *      Fifth               60Mhz-150Mhz

* Note  -  The CPU types are numbers created by Intel, but Intel calls their          
           80586 chip a Pentium, because they wanted to copyright the CPU name.  
           I have left certain technical information out of the above example, 
           for reasons of clarity.


Currently, only 486 and Pentium CPUs are sold in NEW computers so don't expect
to see any of the lower version CPUs in new computers.  If you do, walk away.















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Chapter 3 - Processor


Understanding CPU Speeds (MHz)

     The MHz (pronounced meg'e hurts') of a computer CPU is  how fast (how
much it gets done) the computer runs.  Plain and simple, the larger the MHz 
number; the faster (the more powerful) the computer.  For example:  a 33Mhz 486 


                              PROCESSOR SPEEDS

                  Compared to IBM's first PC (from 1981-1995)

                ------------------------------------------------
                |                                              |
Pentium 150Mhz  |*************************************** 476   |
                |                                              |
Pentium 133Mhz  |************************************ 421      |
                |                                              |
Pentium 120Mhz  |******************************** 381          |
                |                                              |
Pentium 100Mhz  |**************************** 317              |
                |                                              |
Pentium 90Mhz   |************************* 285                 |
                |                                              |
Pentium 75Mhz   |****************** 238                        |
                |                                              |
486 DX2-66Mhz   |********** 144                                |
                |                                              |
386 DX-33Mhz    |***** 35                                      |
                |                                              |
IBM AT-286 8Mhz |** 4                                          |
                |                                              |
IBM PC          |* 1                                           |
                |                                              |
                -|-------|--------|--------|--------|--------|--

                 0      100      200      300      400      500


Figure 2a - The above processor numbers are estimates and intended to show 
            the differences in processor speeds.  I chose not to include the
            Pentium 60Mhz and 66Mhz processors because a Pentium 75Mhz 
            is more powerful for the same money.








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Chapter 3 - Processor


is faster than a 25Mhz 486.  However, that doesn't mean a 66Mhz 486 is faster 
than a 60Mhz Pentium.  Each generation of  CPU is designed to be faster than the
previous generation and that's why a 60Mhz Pentium is roughly 15%-20% faster
than a 66Mhz 486.   Figure 2a gives a graphical view of how CPU's have become
faster over the years.   IBM's very first Personal Computer, the IBM PC, is
considered the basis for all CPU speed comparisons so I've included it in the 
Figure.  Look at how much faster newer computers are compared to the original 
IBM PC back in 1981.

The following shows the price ranges of current processors.  If you would like a
more technical explanation of the differences between these processors, see 
below.


     Pentium 150Mhz
     Pentium 133Mhz      High-End
     Pentium 120Mhz

     Pentium 100Mhz      Middle-Line
     Pentium 90Mhz

     Pentium 75Mhz
     Pentium 66Mhz
     Pentium 60Mhz
     486 DX4-120Mhz
     486 DX4-100Mhz      Low-End
     486 DX2-80Mhz
     486 DX4-75Mhz
     486 DX2-66Mhz
     

Understanding The Difference Between the SX, DX, DX2, and DX4 CPUs

     When Intel introduced the first 386s back in 1985, they also introduced the
computer industry to two new terms, DX and SX.  The letters aren't abbreviations
for anything (or at least Intel never admitted it), but they do tell you a lot 
about a CPU's speed.  In 386 terms, there is a large difference between DX and 
SX CPUs. When comparing processing power, a 386 DX will flat-out run circles 
around a 386











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Chapter 3 - Processor

SX.  A couple of years later Intel introduced the 486 and changed the 
definitions of DX and SX.  Generally speaking, a 486 DX is equal in processing 
power to a 486 SX.  However, the big area where a 486 DX outperforms a 486 SX is 
when the CPU has to do math calculations.  For example:  If you use a program 
that does lots of math calculations (such as CAD, Lotus, etc.), then a 486 DX 
will get the job done considerably faster than a 486 SX.  

     Unfortunately, I need to get "technical" for just a moment to explain a 
very important aspect of CPUs.  Ever since the very first IBM PC, computers have 
been HEAVILY dependent on what is called a Clock chip.  For computers to be 
accurate they have to "think" exactly a certain number of times every second, 
and the clock chip's speed dictates how fast the CPU operates.  Therefore, if 
the clock goes a certain speed then the CPU must go that same speed.  Otherwise, 
the CPU won't work. That was the law until the DX2 and DX4 came on the scene 
(see below).

     Obviously, the CPU isn't the whole computer.  The CPU must communicate
with the disk drives, monitor, mouse, keyboard, etc. and this is called External
processing.  When the CPU does arithmetic operations, decision making, logical
operations, etc. it is doing what is called Internal processing.  Remember this 
and it will all come together in the paragraphs below.

     Shortly after the 486 introduction, Intel introduced a new chip called an
"Overdrive" processor.  The Overdrive processor was designed to be used with
computers that have 486 SX CPUs and the end result is an increase in 
performance. For example:  If I place an Overdrive processor into a 486 SX-25Mhz
(you must have an Overdrive processor socket) then when the computer does
arithmetic operations, decision making, logical operations (remember this is 
called Internal processing), these operations are done at twice (50Mhz) the 
clock speed of the original 486 SX-25 (25Mhz).  Therefore, Externally the 
computer runs at the same speed (25Mhz), but Internally the computer runs at 
50Mhz.  This doubling of the computer speed is called "Clock Doubling"; 
therefore, the Overdrive processor is referred to as a "clock-doubler" 
processor.  The net effect is that the Overdrive processor does everything at 
least as quickly as a 486 SX-25, and many operations twice as fast!  Overall, 
the Overdrive processor will speed up your computer by about one-third to 
one-half.  














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Chapter 3 - Processor


     Again, shortly after Intel introduced the Overdrive processor (Are you
noticing a pattern here?) it introduced a CPU called a DX2.  The DX2 is nothing
more than a 486 DX and an Overdrive processor combined into one processor.
The major benefits of a DX2 are that you get the benefits of an Overdrive 
processor (the clock doubling) at a lower cost since the 486 DX and Overdrive 
processors are cheaper when built together rather than purchased separately.  In 
1993, Intel introduced "clock tripled" processors that are entire processors, 
just like the DX2s, but run at triple the speed of the original clock speed.  
For Example: a 486 DX4-75 runs at a clock speed of 25Mhz Externally and 75Mhz 
Internally.   Intel calls this "clock triplers", but their name for the CPU is 
DX4.  If you are trying to figure out why the name and number don't match; it's 
because of a lawsuit a few years back.  

     Pentium CPUs also use different Internal and External speeds, but because
this was built into the CPU from the start, it has considerably less of an 
impact compared to the 486 CPUs.  Therefore, this is not something you need to 
be concerned with when purchasing a Pentium based computer.  Intel (and several
other companies) have introduced Pentium Overdrive processors designed to be
installed into a 486 computer and are suppose to give a 486 computer the same
speed and power of a Pentium based computer.  However, in my experience they
don't really do the job so I don't recommend you even consider these types of
Overdrive processors.  These Pentium Overdrive processor are expensive enough
that you could almost buy a real Pentium CPU and motherboard to go into your 486
computer.


























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