0
486SX
486SX
They simply make it easier to do floating point instructions.
Before the 486 computers, math processors (or floating point units) in IBM compatibles were optional. The 486DX was the first CPU to include a floating point set as standard equipment. Intel did release the 486SX which was much like the 386DX, which had no floating point set.
Most of the older programs that required floating point instructions were compiled with floating point libraries. These were instructions that used the CPU to emulate a math coprocessor. The software would call the floating point command just like the coprocessor was there. The CPU would throw an exception that it didn't understand the command, then the exception handler would send the command to the floating point library which would then execute it.
But these routines were slow and the CPU had to be tied up to run them. A lot of the floating point libraries also had floating point processor detection routines. So if a math coprocessor was detected, then all the software interrupts used by the emulator sets would be routed to the math coprocessor. So when the CPU refuses to execute an instruction, the coprocessor takes over.
In certain cases, the CPU can continue with the next instructions while the FPU is busy if there is no risk of a race condition. A race condition is when there is a chance that the result might not be there when it is needed. For instance, you don't want the CPU to process the results of the FPU before the results arrive, or the CPU will get random garbage from memory and act the next instruction upon the garbage. Then the FPU puts its result in that area of memory too late. So one way around that is the FWAIT instruction. That pauses the CPU while the FPU finishes to prevent a race condition.
Send tips (with links to source of data) or corrections to MoboCop ; 1924 : The Tabulating Machine Company is renamed to IBM. ; 1939 : Hewlett Packard is founded. ; 1947 : The first transistor is invented. ; 1957 : DEC is founded. ; 1966 : MoboCop was born. ; 1967 : IBM creates the first floppy disk. ; 1968 : Intel Corp is founded. ; 1969 : AMD is founded. : AT&T Bell Laboratories develop Unix. : Compuserve is founded. ; 1970 : Intel releases the first microprocessor - the 4004. : Intel announces the 1103, the first random-access memory (RAM). ; 1972 : The compact disc is invented. ; 1974 : Intel releases the 8080 microprocessor. ; 1975 : MITS ships one of the first PCs, the Altair 8800 with one kilobyte (KB) of memory: A mail-order kit for $397.00 : Paul Allen and Bill Gates and found Microsoft. : Steve Wozniak and Steve Jobs found Apple Computer. ; 1976 : Intel introduces the 8086 microprocessor. : Xerox develops the widely used networking protocol Ethernet. ; 1977 : Star Wars debuts. : ARCNET the first commercially network is developed. : The Apple II, the first personal computer with color graphics is demonstrated. ; 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