The x86 CPUs provide 20 basic instruction classes. Seven of these instructions have two operands, eight of these instructions have a single operand, and five instructions have no operands at all. The instructions are mov (two forms), add, sub, cmp, and, or, not, je, jne, jb, jbe, ja, jae, jmp, brk, iret, halt, get, and put. The following paragraphs describe how each of these work.

The get and put instructions let you read and write integer values. Get will stop and prompt the user for a hexadecimal value and then store that value into the ax register. Put displays (in hexadecimal) the value of the ax register.

The remaining instructions do not require any operands, they are halt and brk. Halt terminates program execution and brk stops the program in a state that it can be restarted.

Posted on 2003-06-23 20:17:16 by comrade

Must be one of those undocumented opcodes like CreateWindowEx

HLT is real though
Posted on 2003-06-23 20:23:29 by donkey
Yes, HLT but not HALT.
Posted on 2003-06-23 20:28:52 by comrade

To understand how to improve system performance, it's time to explore the internal operation of the CPU. Unfortunately, the processors in the 80x86 family are complex beasts. Discussing their internal operation would probably cause more confusion than enlightenment. So we will use the 886, 8286, 8486, and 8686 processors (the "x86" processors). These "paper processors" are extreme simplifications of various members of the 80x86 family. They highlight the important architectural features of the 80x86.

The 886, 8286, 8486, and 8686 processors are all identical except for the way they execute instructions. They all have the same register set, and they "execute" the same instruction set. That sentence contains some new ideas; let's attack them one at a time

So I guess those are the intructions for the "paper processors".
Using x86 as the title only serves to confuse things however.

Posted on 2003-06-23 20:29:36 by RobotBob
Anyway the HLT instruction acts more like the imaginary BRK instruction. It allows execution to continue if I recall. I don't have an intel manual handy to check.
Posted on 2003-06-23 20:36:42 by donkey
All it does is to wait for an interrupt, it has nothing to do with terminating the program.
Posted on 2003-06-24 16:28:16 by Sephiroth3