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CFloppyDisk 2.0

, 14 Feb 2002 CPOL
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A class for reading and writing floppy disk sectors directly [Win 95/98/ME/NT/2K/XP]

What this class is for?

CFloppyDisk is a class that allows you to read and write physical floppy disk sectors directly. The class provides static member functions for resetting the floppy disk controller, for reading a physical sector and for writing a physical sector. I am using the term, physical sector, to avoid confusion with absolute sectors.

Honestly, these three functions might as well have been put into a single header file and distributed as a sort of source code library. But I made it a class, so that people will find it easier to use it. These days people prefer classes for everything.

Why this class was made?

In Windows NT/2000 we can read and write directly onto a floppy disk by using the CreateFile API call. You can simply open \\.\A: 

Unfortunately this technique will not work under Windows 95, 98 and ME. This probably is an indicator that underneath the GUI, ME is more 98 than 2000 as is popularly believed. Well that shortcoming is now solved. This class will serve you well, I hope.

One class - Any OS

As I just mentioned there is a huge difference in the techniques used for directly accessing a floppy in the NT/2K set of Operating Systems and the Windows 9x/ME set of Operating Systems. With this class, you need not bother with what version of Windows your program will be running on. Internally the class has separate sets for functions, but the user can simply call the generic functions. The class will make the required OS version checks and call the appropriate function internally.


  • You must be running one of Windows 95/98/ME/NT/2K/XP

Using the class.

There are three static functions which you can use. Thus you should not instantiate the class. Simply include the header file and call the static functions directly.


static void ResetDisk()

ResetDisk resets the floppy disk controller and drive. It does not do anything to the floppy disk. But the floppy drive's read/write head will be recalibrated. Normally you might want to start off a series of reads and writes with a controller reset. But you must also use this when you get an error. If you do not reset the controller after an error, then consequent behavior of the disk controller will be random and unpredictable.


static int ReadFloppyDisk(BYTE *buffer, WORD cylinder, WORD sector, WORD head)

ReadFloppyDisk is used to read a single physical sector into a buffer. Floppy disk sectors are 512 bytes for most standard floppies. So buffer should be allocated at least 512 bytes. You might want to find out the number of bytes per sector, that your floppy drive supports. The other parameters are cylinder, sector and head which are the physical parameters required to specify where you want to read the sector from. This function will return 0 for success and non-zero for failure, make sure you check the return value, always.


static int WriteFloppyDisk(BYTE *buffer, WORD cylinder, WORD sector,WORD head)

WriteFloppyDisk is the analogous function to ReadFloppyDisk that does just the opposite. It writes the bytes contained in buffer onto the physical sector specified by cylinder, sector and head. This function will return 0 for success and non-zero for failure, make sure you check the return value, always.

Some points to remember

The floppy drive motor might take some time to catch up with our function calls. These functions will not wait for that to happen. So you must be careful that you do not do successful reads and writes onto the same sector till you are sure the data has been successfully read from or written into the sector in question. Often you will find that the functions return failure. This happens because most floppy drives are now thoroughly unused or over-used and are often in a very bad state. The quality of floppy diskettes also leaves a lot to be desired. The solution is to loop all calls thrice.

For example, if you are performing a read or a write, call the function and if it fails, call it again. Repeat this three times. I have found that three times is a pretty alright number to get a reasonable success rate. Also, it helps if you call the reset function after long operations. And please remember that the floppy drive is the slowest working part in your computer and keep that in mind. What that means is, don't try to rush it. If you are writing critical information into a sector, perhaps for copy protection, then it would be a good idea to use a Sleep in between.

Example usage

void CCFloppyDiskTestDlg::OnButton1() 
    unsigned char buff[512];	
    strcpy((char*)buff,"This is kinda cool");
        MessageBox("write failed");
        MessageBox("read failed");

How to loop calls to improve success rate.

int m_return_code;
int count=0;
    MessageBox("After three attempts, we still failed. Destroy the floppy");

Technical Note regarding ResetDisk

Under Windows NT/2K we cannot directly make Interrupt 13h calls. For the Win 9x/ME set of Operating Systems the class makes a call to Interrupt 13h Function 0h which resets the floppy disk controller. To achieve the same in the Windows NT/2K set of Operating Systems, I have taken a different approach.

Initially I took the mistaken attitude that Windows NT/2K will not have resetting problems, but unfortunately I was wrong. Then I was stuck with the problem of resetting the internal buffers and error flags that NT/2K maintains when a floppy disk is directly opened. That's when I found out that all I had to do was to open the floppy disk and then close it immediately. I tried this out with bad floppies. And my success percentage improved from a very low 20% to almost 95% [I still got the occasional error]. But that can be improved to 99.999% by using the triple-loop method I have mentioned above. I believe what happens is that when we close the file handle, NT/2K flushes its internal buffers. This might internally result in a resetting of the floppy drive. I am not certain about this but that inference seems highly probable.

Version History

  • Version 2.0 - This now supports Windows 95/98/ME/NT/2K/XP
  • Version 1.0 - This supported only Windows 95/98/ME


Todd C. Wilson - It was Todd who suggested that I write a combined version of the class that supports both sets of Operating Systems. I owe version 2.0 to Todd.

Michael Dunn & Tim Smith - As you might observe, if you look through the source code, the entire functionality of the class is implemented via static functions. And I badly wanted some kind of static construction for some of my static members via calls to static functions. Without Tim's and Mike's help, I'd still have been sitting here puzzled and swearing at Microsoft.


This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


About the Author

Nish Nishant

United States United States
Nish is a real nice guy who has been writing code since 1990 when he first got his hands on an 8088 with 640 KB RAM. Originally from sunny Trivandrum in India, he has been living in various places over the past few years and often thinks it’s time he settled down somewhere.
Nish has been a Microsoft Visual C++ MVP since October, 2002 - awfully nice of Microsoft, he thinks. He maintains an MVP tips and tricks web site - where you can find a consolidated list of his articles, writings and ideas on VC++, MFC, .NET and C++/CLI. Oh, and you might want to check out his blog on C++/CLI, MFC, .NET and a lot of other stuff -
Nish loves reading Science Fiction, P G Wodehouse and Agatha Christie, and also fancies himself to be a decent writer of sorts. He has authored a romantic comedy Summer Love and Some more Cricket as well as a programming book – Extending MFC applications with the .NET Framework.
Nish's latest book C++/CLI in Action published by Manning Publications is now available for purchase. You can read more about the book on his blog.
Despite his wife's attempts to get him into cooking, his best effort so far has been a badly done omelette. Some day, he hopes to be a good cook, and to cook a tasty dinner for his wife.

Comments and Discussions

GeneralData copy protection from one CD to anather CD Pinmembersushilabhanvar23-Jun-09 21:40 
QuestionHow to detect bad sector in drive.Please help. Pinmemberwant2beboss19-Jul-07 16:44 
QuestionOther Removable Dvices PinmemberAlexQII20-Apr-07 13:14 
GeneralRead/Write permission PinmemberVC_RYK2-Apr-07 0:51 
Questionreading 1024 Byte / 5 sec / 800 KB Pinmemberdudi_33322-Dec-06 5:08 
QuestionFloppies and .net DLL PinmemberRealJunk2-Dec-06 21:34 
GeneralIt doesn't work Pinmemberfan wei fang28-Dec-05 8:18 
GeneralRe: It doesn't work PinstaffNishant Sivakumar29-Dec-05 9:48 
GeneralRe: It doesn't work Pinmemberfan wei fang29-Dec-05 16:01 
QuestionCan you help me ???. help me (absread() , abswirte()) PinmemberMinh Vuong Tran11-Dec-05 17:35 
AnswerRe: Can you help me ???. help me (absread() , abswirte()) Pinmemberhans_artmann21-Apr-06 14:07 
Generalfloppy or cd-rom PinmemberBest_student13-Feb-05 22:58 
GeneralHelp me Pinmembersos1184-Dec-04 20:44 
QuestionHow to find a unused sector in disk? Pinmembergreenolive_bing14-Oct-04 16:08 
GeneralAccess From PinmemberSwaimRM13-Oct-03 7:49 
GeneralNice nice Pinmember=[ Abin ]=16-Sep-03 15:11 
This is a good class that I've been looking for. Thanks.
One suggestion though, since you recommend three retries after failed read/write, why don't you simply integrate the retries in to your code? I got read/write frequently if I don't try for 3-5 times and it's a bit burdensome having to keep retrying to call a function, so it'd be nice if your class handles that by itself. For example:
class CFloppyDisk
    static int ReadFloppyDisk(BYTE *buffer, WORD cylinder, WORD sector, WORD head, int nRetry = 5);
   /* Other class members... */
    // This function actually reads from floppy
    static int __Read(BYTE *buffer, WORD cylinder, WORD sector, WORD head);
int CFloppyDisk::ReadFloppyDisk(BYTE *buffer, WORD cylinder, WORD sector, WORD head, int nRetry)
    int nRes;
        nes = __Read(buffer, cylinder, sector, head);
    } while (n != 0 && nRetry > 0);
    return nRes;

Question800kB floppies 80 tracks, 10 sectors - any chance? Pinmemberhans_artmann16-Aug-03 6:05 
GeneralThank you, Nish!!! PinmemberPJ Arends11-Aug-03 10:57 
GeneralRe: Thank you, Nish!!! PineditorNishant S11-Aug-03 16:30 
GeneralFloppy write protection PinsussAnonymous12-May-03 6:37 
GeneralReading cd sectors PinsussDhruvJayal22-Apr-03 22:17 
QuestionCan you tell me how I can format the floppy disk by programming? PinmemberWei Huang19-Feb-03 1:25 
GeneralThanks Nish PineditorAndrew Peace1-Sep-02 13:30 
GeneralRe: Thanks Nish PineditorNishant S1-Sep-02 16:04 
QuestionFormatting a Disk? PinmemberMyself26-Jul-02 18:14 

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