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Over the years, Intel also released a 287 math coprocessor for the 286 chip, and a 387 for the 386. But with the release of the Intel 486DX in 1989, the FPU was built right into the CPU itself. No longer was it an option! Unfortunately, in 1991 Intel released a lower-cost 486SX that did not have the built-in FPU and instead offered a 487SX math coprocessor as an option. With the 1993 release of the Pentium, however, the built-in FPU became standard again, perhaps for all time. Motorola integrated an FPU with its 68040 microprocessor, which was released in 1990. Previously Motorola sold 68881 and 68882 math coprocessors to support the earlier microprocessors in the 68000 family. The PowerPC chips also have built-in floating-point hardware.

Although hardware for floating-point arithmetic is a nice gift for the beleaguered assembly-language programmer, it's a rather minor historical advance when compared with some other work that began in the early 1950s. Our next stop: computer languages.

Chapter 24. Languages High and Low

Programming in machine code is like eating with a toothpick. The bites are so small and the process so laborious that dinner takes forever. Likewise, the bytes of machine code perform the tiniest and simplest of imaginable computing tasks—loading a number from memory into the processor, adding it to another, storing the result back to memory—so that it's difficult to imagine how they contribute to an entire meal.

We have at least progressed from that primitive era at the beginning of Chapter 22, in which we were using switches on a control panel to enter binary data into memory. In that chapter, we discovered how we could write simple programs that let us use the keyboard and the video display to enter and examine hexadecimal bytes of machine code. This was certainly better, but it's not the last word in improvements.

As you know, the bytes of machine code are associated with certain short mnemonics, such as MOV, ADD, CALL, and HLT, that let us refer to the machine code in something vaguely resembling English. These mnemonics are often written with operands that further indicate what the machine-code instruction does. For example, the 8080 machine-code byte 46h causes the microprocessor to move into register B the byte stored at the memory address referenced by the 16-bit value in the register pair HL. This is more concisely written as

MOV B,[HL]

Of course, it's much easier to write programs in assembly language than in machine code, but the microprocessor can't understand assembly language. I've explained how you'd write assembly-language programs on paper. Only when you thought you were ready to run an assembly-language program on the microprocessor would you hand-assemble it, which means that you'd convert the assembly-language statements to machine-code bytes and enter them into memory.

What's even better is for the computer to do this conversion for you. If you were running the CP/M operating system on your 8080 computer, you'd already have all the tools you need. Here's how it works.

First you create a text file to contain your program written in assembly language. You can use the CP/M program ED.COM for this job. This program is a text editor, which means that it allows you to create and modify text files. Let's suppose you create a text file with the name PROGRAM1.ASM. The ASM file type indicates that this file contains an assembly-language program. The file might look something like this:

ORG 0100h

LXI DE, Text

MVI C,9

CALL 5

RET

Text: DB 'Hello!$'

END

This file has a couple of statements we haven't seen before. The first one is an ORG (for origin) statement. This statement does not correspond to an 8080 instruction. Instead, it indicates that the address of the next statement is to begin at address 0100h, which you'll recall is the address where CP/M loads programs into memory.

The next statement is an LXI (Load Extended Immediate) instruction, which loads a 16-bit value into the register pair