MS-DOS uses INT 21H for its main API functions which provide a low-level is the assembly code to transfer data from one file to other using INT 21H?. INT is an assembly language instruction for x86 processors that generates a software interrupt. For example, INT 21H will generate the software interrupt 0x21 (33 in decimal), causing the function pointed to by the 34th vector in the interrupt. int 21h Dos Interrupt. Int 21h is a common function. The INT 21H instruction in is a software interrupt to vector 21H. It is used for input/output operations.

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This is accomplished by entering a bit value corresponding to a kernel function into the EAX register of the processor and then executing INT 0x INT is an assembly language instruction for x86 processors that generates a software interrupt. This page was last edited on 8 Octoberat Since the dedicated 0xCC opcode has some desired special properties for debugging, which are not shared by the it two-byte opcode for an INT 3, assemblers do not normally generate the generic 0xCD 0x03 opcode from mnemonics.

It comes under type 21h of various interrput tables, hence the lines of code goes like these as you mentioned. INT X where X is the software interrupt that should be generated This simply means that you are using function 01h of the Interrupt type Most Unix systems and derivatives do not use software interrupts, with the exception of interrupt 0x80, used to make system calls.

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Other INT instructions are encoded using two bytes.

INT (x86 instruction)

By calling it with different parameters in the registers mostly ah and al you could access various IO operations, string output and more. By clicking “Post Your Answer”, you acknowledge that you have read our updated terms of serviceprivacy policy and cookie policyand that your continued use of the website is subject to these policies.

By using this site, you agree to the Terms of Use and Privacy Policy. Philip Kirkbride 7, 26 82 21hh INT 3 instruction is defined for use by debuggers to temporarily replace an instruction in a running program in order to set a breakpoint.

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Instruction Set Reference Manual”. I’m new to learning assembly language, and I’m wondering what the command int 21h means.

BOSS 8 23 For example, In 21H will generate the software interrupt 0x21 33 in decimalcausing the function pointed to by the 34th vector in the interrupt table to be executed, which is typically a DOS API call.

It takes the interrupt number formatted as a byte value. Abraham Jacob 51 1 1.

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int 21h Dos Interrupt

Stack Overflow works best with JavaScript enabled. Views Read Edit View history. One of the most useful DOS software interrupts was interrupt 0x Email Required, but never shown.

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What does “int 21h” mean in Assembly? – Stack Overflow

Post Your Answer Discard By clicking “Post Your Answer”, you acknowledge that you have read our updated terms of serviceprivacy policy and cookie policyand that your continued use of the website is subject to these policies. It is therefore entirely possible to use 12h far-call instruction to start the interrupt-function manually after pushing the flag register.

Depending on the context, compileror assemblera software interrupt number is often given as a hexadecimal value, sometimes unt a prefix 0x or the suffix h. Retrieved from ” https: Sign up using Email and Password. When generating a software interrupt, lnt processor calls one of the functions pointed to by the interrupt address table, which is located in the first bytes of memory while in real mode See Interrupt vector. Thanks in advance for your answer.

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