From: boltz@chopin.psu.edu (Mark Boltz)
Newsgroups: comp.sys.ibm.pc.misc,comp.sys.ibm.pc.hardware
Subject: Those Intel Processors (what is SX/DX)
Summary: An explanation of Intel processor designations for i8088 family
Keywords: bananas, Fahrvergnugen
Date: 4 Sep 92 02:40:17 GMT
Organization: Penn State University

Someone asked awhile ago what the DX and SX meant for intel's processors,
so I thought I would try to straighten out the confusion.  This info is 
coming from a copy of Intel's Product Overview 1992, so it isn't *completely*
up-to-date, but close.

8088
   8 bit bus (data)
  16 bit internal data path
   5, 8 Mhz clock frequency
   1 MB memory addressability
  no virtual memory
  64 KB I/O addressability
  8087 math coprocessor

8086
  16 bit data bus
  16 bit internal data path
   5, 8, 10 Mhz clock frequency
   1 MB memory addressability
  no virtual memory
  64 KB I/O addressability
  8087 math coprocessor

80286 (80186 used in embedded control market, not pc's)
  16 bit data bus
  16 bit internal data path
   8, 10, 12, 16 Mhz clock frequency
  16 MB memory addressability
  64 KB I/O addressability
     virtual memory
  80287 XL/XLT math coprocessor

80386 SX
  16 bit data bus
  32 bit internal data path
   16, 20 Mhz clock frequency
  16 MB memory addressability
     virtual memory
  64 KB I/O addressability
  80387SX coprocessor

80386 SL
  16 bit data bus
  32 bit internal data path
  20, 25 Mhz clock frequency
  32 MB memory addressability
     virtual memory
  64 KB I/O addressability
  80387SX coprocessor
        SL developed for notebook computers, also differentiates itself
   from the others with built-in disk controller, wait-state logic and
   a cache that the other 386s don't have - optimizes its power usage

80386 DX
  32 bit data bus
  32 bit internal data path
  16, 20, 25, 33, 40 Mhz
   4 GB memory addressability
     virtual memory
  64 KB I/O addressability
  80387 DX coprocessor
80486 SX
  32 bit data bus
  32 bit internal data path
  16, 20, 25 Mhy
   4 GB memory addressability
     virtual memory
  64 KB I/O addressability
  80487SX coprocessor

80486 DX
  32 bit data bus
  32 bit internal data path
  25, 33, 40, 50 Mhz
   4 GB memory addressability
  64 KB I/O addressability
  coprocessor built-in
  
Both 486s have an 8KB internal cache on the chip.
As seen above the 386 DX/SX difference lies in the external data bus bit
size.  The SX, although similar to the DX, has to wait longer to process
information, because it can only receive it in 16 bit chunks, rather than
the 32 bit stuff the DX gets fed.  It is faster than a 286, but slower than
the 386 DX.  Why do this?  Intel found its monopoly on microprocessors for
PC's pinched with the introduction of American Micro Devices (?) or AMD.
The Am386 is a better chip, IMHO.
The difference between the 486 SX/DX is, for similar reasons, one has a
coprocessor built into the chip, the other (SX) doesn't.  Rumor has it this
was an accident, that Intel had 486 chips with defective coprocessors, so to
unload them, they marketed them as such.

The 486 DX/2 is a 486DX with a normal external clock rate of 25 or 33 Mhz,
but the chip itself is running at twice that external rate.  (ie 50 or 66 Mhz)

The 486 Overdrive is (basically) a 486 DX with the processor turned off, but
with a functioning coprocessor.  It is NOT a 487SX, which is just a coproc.,
because the Overdrive has the advantage of the extra 8 KB cache and other
internal support functions.  I believe this goes in the copro socket, and
will still allow a regular 487SX to 'piggy back' it.
   Neat concept, that you can have a 486SX with an overdrive and a 487SX, and
come out with a faster machine than the 486-40.  You spend a lot more on the
chip stuff tho. *shrug*

Hope that helps cut through some of the confusion.
(Any glaring errors are probably typos...if not, blame Intel, its THEIR book.

---------
boltz@vivaldi.psu.edu

Intel Product Overview 1992 (c) 1992 Intel Corporation
The processor types are trademarks of the Intel Corporation.