boone@athena.cs.uga.edu (Roggie Boone) (02/08/91)
I know this has probably been asked before, but I am new to this group. Could someone please explain or direct me to an article that explains in some detail the difference(s) between a full 80386 microprocessor (80386DX) and the 80386SX? Are they both 32-bit processors? I've heard that the main difference is that the SX "talks" to the outside world (memory, disk, etc) at 16-bits while the DX uses 32 bits. Is this true and is this the only difference? Are there any limitations on the 386SX running 386-specific software? _Any_ info that can be provided (technical or not) would be appreciated. Thanks in advance. Roggie Boone (boone@athena.cs.uga.edu) University of Georgia
timd@hotwheel.dell.com (Tim Deagan) (02/08/91)
In article <1991Feb7.182436.17262@athena.cs.uga.edu>, boone@athena.cs.uga.edu (Roggie Boone) writes: > I know this has probably been asked before, but I am new to this group. > > Could someone please explain or direct me to an article that explains in > some detail the difference(s) between a full 80386 microprocessor > (80386DX) and the 80386SX? Are they both 32-bit processors? I've > heard that the main difference is that the SX "talks" to the outside > world (memory, disk, etc) at 16-bits while the DX uses 32 bits. Is this > true and is this the only difference? Are there any limitations on > the 386SX running 386-specific software? > > _Any_ info that can be provided (technical or not) would be appreciated. Your description of the difference is accurate. Internally the SX and DX have the same bus, 32-bits. All the internal registers are the same, as are the protected mode features. To the outside world the SX looks the same as a 286, a 16-bit external bus. Perfectly adequate for all the ISA (AT) bus cards out there now. This is the same trade-off INTEL made when they started the whole PC thing by taking the 8086 16-bit processor and making an external 8-bit version called the 8088. The SX comes in two official flavors, 16 and 20 MHz. Most DX's are 20 or 25 MHz. The SX has had some reported problems with protected mode applications such as WIN 3.0, but most all of these have been traced down to the chip-set the CPU was glued to. There is one technical consideration with 386SX's, it'll only matter to HW developers but it is frustrating, the SX only comes in one package, PQFP, the Plastic Quad Flat Pack. Only one company sells a chip-clip and it costs hundreds of dollars and takes 6-8 months to ship, if ever. So, hardware debugging is a MAJOR bitch. Small point, but it can completely stymie development in a pinch (inverse assembling and such is impossible). There are some differences such as prefetch queue size which are invisible and probably won't matter to anyone. Price wise the SX, especially with caching, can be a good deal. It all depends on what you want to do. I'd probably buy one if the price were right. ------------------------------------------------------------------------ ------------------"Wake up! Wake up!" - Spike Lee --------------------- ------------------------------------------------------------------------ Rev. Tim Deagan timd@hotwheel.dell.com timd@twaddle.dell.com
johnk@cpqhou.uucp (John Kennedy) (02/09/91)
In article <1991Feb7.182436.17262@athena.cs.uga.edu> boone@athena.cs.uga.edu (Roggie Boone) writes: >I know this has probably been asked before, but I am new to this group. > >Could someone please explain or direct me to an article that explains in >some detail the difference(s) between a full 80386 microprocessor >(80386DX) and the 80386SX? Are they both 32-bit processors? I've >heard that the main difference is that the SX "talks" to the outside >world (memory, disk, etc) at 16-bits while the DX uses 32 bits. Is this >true and is this the only difference? Are there any limitations on >the 386SX running 386-specific software? > >_Any_ info that can be provided (technical or not) would be appreciated. > >Thanks in advance. > >Roggie Boone (boone@athena.cs.uga.edu) >University of Georgia To the programmer, i.e. to software, the SX looks exactly like a DX. Well, not EXACTLY, but the differences are minor minor minor. The DX has a 4 GB address space (32 bits), while the SX has only a 16 MB (24 bits) address space. Also, the SX requires a 387SX co-processor, the DX can use either a regular 387 or a 287. ------------------------------------------------------------------------------- John R. Kennedy | Most applications of the 80386 will use real Compaq Computer Corporation | mode for initialization only. | uunet!cpqhou!johnk | -- 80386 Programmer's | Reference Manual "Don't tread on me." | -------------------------------------------------------------------------------
pasquale@sgl (Pasquale Leone) (02/11/91)
In article <1991Feb7.182436.17262@athena.cs.uga.edu> boone@athena.cs.uga.edu (Roggie Boone) writes: >I know this has probably been asked before, but I am new to this group. > >Could someone please explain or direct me to an article that explains in >some detail the difference(s) between a full 80386 microprocessor >(80386DX) and the 80386SX? Are they both 32-bit processors? I've >heard that the main difference is that the SX "talks" to the outside >world (memory, disk, etc) at 16-bits while the DX uses 32 bits. Is this >true and is this the only difference? Are there any limitations on >the 386SX running 386-specific software? > You canNot write a program that can distinguish between a 386SX and a 386DX. It therefor is obviuos that an SX can run ANY software that a DX can run (though somewhat slower because of the restricted data path). Anyone who tells you different is either trying to sell you a DX or is a software type who thinks hardware is strange art that nobody quite understands. Intel may have built some pretty idiotic chips in the past but they seem to know what they are doing now. The big reason the SX chip is cheaper than the DX (other than marketing) is that the DX is packaged in a ceramic PGA (pin grid array) package and the SX is in a plastic quad flat pack. Look up the price of any chip which comes in both package types and you'll see that the PGA is usually about twice the price of the quad flat pack. pasquale@sgl.ists.ca