wangf@unixg.ubc.ca (Frank Wang) (06/12/91)
My friend bought a 486-25. He said he did not order the
co-processor (something like Weitek co-processor). I know that 486
has the feature of built in math co-processor. But what is
this co-processor for? Why is there another co-processor appeared
after Intel integrated the math co with cpu? My friend could not
explain the function of this "Weitek" co-processor. Can any one
out there tell me what this co-processor is and why?
Thanks in advance.pshuang@ATHENA.MIT.EDU (06/13/91)
In article <1991Jun12.071753.2030@unixg.ubc.ca> wangf@unixg.ubc.ca (Frank Wang) writes: > My friend bought a 486-25. He said he did not order the > co-processor (something like Weitek co-processor). I know that 486 > has the feature of built in math co-processor. But what is > this co-processor for? Why is there another co-processor appeared > after Intel integrated the math co with cpu? My friend could not > explain the function of this "Weitek" co-processor. Can any one > out there tell me what this co-processor is and why? I think Intel, with its latest introduction of chips, has muddied up the waters in regards to math coprocessors. Here's a summary: * The 386SX and i386DX, like previous families of chips from Intel, do not contain math coprocessor on the main CPU chip. The 80387SX and 80387DX chips can be purchased from Intel and placed into a co-processor socket to provide improved math performance. Currently, there are at least two companies (Cyrix, ITT; possibly AMD?) which can sell you plug-compatible (i.e. uses same socket as Intel chips and software can't tell the difference between them and real 80387's) chips which can replace the equivalent chips from Intel; they offer a better price-performance ratio. Weitek designed another family of math coprocessors which are *NOT* plug- or software-compatible with 80387's, meaning that motherboard manufacturers have to design a special socket for them, and software writers have to provide special support. However, they provide *MUCH* better performance... at a higher cost. Whereas a number of mainstream applications support the 80387 coprocessor, fewer applications support the Weitek line, usually only scientific, engineering, and other applications which are extremely numeric-intensive (spreadsheets are usually *NOT* in this category). * The i486 chip, as originally introduced, contained an on-chip equivalent (software-compatible) to the 80387 chip; performance was better than a i386+387 combination, however, because the CPU and NPU (numeric processing unit) in the i486 can be more closely integrated. Weitek extended its coprocessor line to include a coprocessor that can work with the i486 chip, again *MUCH* faster than the i486 chip by itself. Intel's new product, the i486SX, is essentially a normal i486 sans a working on-chip NPU. The i487 chip (also newly introduced) is designed to be used in i486SX systems as an upgrade which essentially completely replaces the old CPU (and therefore should not be referred to as a coprocessor) with the new one which has both a CPU and NPU, looking remarkably like the original i486 chip in the first place, and prompting current flamage about Intel's marketing practices. Singing off, UNIX:/etc/ping instantiated (Ping Huang)
jgay@digi.lonestar.org (john gay) (06/13/91)
From article <1991Jun12.071753.2030@unixg.ubc.ca>, by wangf@unixg.ubc.ca (Frank Wang): > My friend bought a 486-25. He said he did not order the > co-processor (something like Weitek co-processor). I know that 486 > has the feature of built in math co-processor. But what is > this co-processor for? Why is there another co-processor appeared > after Intel integrated the math co with cpu? My friend could not > explain the function of this "Weitek" co-processor. Can any one > out there tell me what this co-processor is and why? The Weitek co-processor is a memory-mapped math co-processor (unlike Intel's interrupt driven co-processor). The memory-mapped Weitek is supposed to be faster than the Intel, but with the '486 I am not sure this is still true. The Weitek has to have compilers that will create code for it (usually more expensive) and is itself expensive around $1000 I think. Why - more floating point speed (at least as far as '386 version). > Thanks in advance. welcome. -- john gay. jgay@digi.lonestar.org Like Thoreau, I rejoice that there are owls. Part of the reason is that owls eat mice, and thus make a certain number of cats unnecessary, which is always a plus. Jeff Duntemann, Dr. Dobb's June '91