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ComputerTalk Magazine 2
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ART2
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1992-07-27
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These are some of the questions that have passed my desk.
Q. What is meant by conventional, EXPanded, and EXTended memory?
A. These are the three types of memory recognized by IBM and compatible
computers. They are best described as follows:
Conventional - The 8086 and 8088 could directly address 1 megabyte
of memory. Thus, the memory between 0 and 1024K is conventional memory.
The first 640K was set as the maximum that DOS and applications
could address. The remaining 384K is used by video RAM, BIOS, and/or RAM
for hardware cards. Some system now, via remapping, can free up this 384K
for use as cache or RAM drives.
This is the reason that today programs still are made to run in the
640K limit. However, by using extenders on more powerful systems, this can
be overcome.
Both of the following are memory above the initial 1024K mentioned above.
EXPanded Memory or Expanded Memory Specification(EMS) - This is
also referred to as LIM EMS, a joint venture by Lotus, Intel, and Microsoft
(LIM), to break the 640K barrier. By using a memory card, such as the Intel
AboveBoard, users with 8086, 8088, or 80286, can expand their memory beyond
the 1 MB area. On these systems you install software, which is provided
with the card, to access this memory. It can be used as cache, RAM disk or
with programs that can utilize it.
To use this memory on a 80386 or higher, you would use an expanded
memory manager, to covert the EXTended memory of these systems, into
EXPanded memory. Programs that do this are QEMM/386, and 386MAX, to name a
few. Quite a few programs do NOT see EXTended memory. This is the reason
you have to convert it.
EXTended Memory - This can only be used on 80286 and higher
computers. This type of memory is used mainly in protected mode
applications. Examples of these are, OS/2, Windows, DESQview.
Q. What is the difference between 80386, 80386SX, 80386DX, 80486, and
80486SX?
A. When the 80386 chip was first made, there was NOT an SX, so the chip was
the 80386. Then along came the SX. Now people were confused with the ads
and talk about 386 and 386SX. So, in a move to further confuse people, they
came up with the DX. The 80386, 80486, 80386DX, and 80486DX, are the same
computers. The 386 and 386DX mean the same thing. A true 80386 chip. The
same applies for the 486 and 486DX.
Now that this is squared away, we will explain the SX. The SX was a
inexpensive way to get a 386 at a bit more than 286 prices. At the time
that the SX was released, the 386 was a high-priced computer. This was a
way to get people into the 386 computer without the cost. However, as will
be listed below there are differences between a true 386 or 486, and the
SX.
80386 (80386DX) - A true 32-bit multitasking microprocessor that
address 4GB (gigabytes) of physical memory and uses a 32-bit data bus.
80386SX - This runs at slower speeds than a true 386, usually
16-20Mhz. It also uses a 16-bit data bus.
80486 (80486DX) - Also listed as i486. A 32-bit multitasking
microprocessor with built-in math coprocessor. Rated at running two to
three times as fast as a 386.
80486SX - Lower speed version of above. Does not have a math
coprocesor. The 80487 is available as an option.
I still feel that the SX is a good entry-level computer. Buying a
computer today, you should NOT buy anything less than a 80386SX-20.