Estex: Disk SubSystem (DSS) Programming Guide
Table of Contents
 HYPERLINK "" \l "intro" 1. Introducing  HYPERLINK "" \l "identify" 2. Identification of system functions  HYPERLINK "" \l "diskfunc" 3. Disk devices functions 

1. Introducing
   This document contains the list of functions and concepts of interaction with a disk subsystem.    DSS is a collection of very useful functions that reside in DSS itself, ready for use by any your programs. These functions are stored in library SYSTEM.DOS and allow management of files, memory allocation, loading and execution of the programs.  File specification     The file specification is a string, containing a names of disk, directories separated by a symbol "\" and name of file. The names of disk drive and directories can be discard. for example:  C:\TEXT\DOC\text.doc  A:file.txt  \TEXT\info.txt     The DSS used chars with colon suffix as names of disk devices (A:, B:, C: etc.) The name of disk can be written down before filename for specified disk there it placed. For example: command DIR C:DATFILE searches for DATFILE in the current directory of disk C:.    When disk name not specified DSS used current disk. At start DSS, the current disk is a disk whence was loaded DSS.    The filenames consist of two parts. The first part contain 8 chars of file name. The second part is not necessary and contain 3 chars of file type (also known as extentsion). At the writing of filename, both parts are separated by char point. For example: the names "NAME" and "NAME." is specified same file. In the name don't allows symbols with codes less 32 and chars . " / \ [ ] : | < > + = ; ,     As the subdirectories files too, their names are formed by same way. The name of root directory always "\". And each subdirectories contain two items with names "." and "..". The name "." specified a current directory and name ".." specified name of parent(uplevel) directory.    Some console commands and DSS functions allow to use global symbols ? and * which can be used for filename templates.    The symbol ? means that any one char of filename. The symbol * means that it char can be replaced by any symbols.  For example: *.txt - means, all files with type "txt" a??.* - means, files which contain three or less symbols and first symbol is "a" dc*.exe - means, files with type "exe" and began "dc"  File attributes     The each bit of byte attributes specified various attribute. And It can be changed by DSS function.  bit 0 - Read only bit 1 - Hidden bit 2 - System bit 3 - Volume label bit 4 - Directory bit 5 - Archive bit 6 - Reserved bit 7 - Reserved     Attribute "read only". When value is 1, file can be read, but can't be written or deleted.    Attribute "hidden". When value is 1, DSS can't manipulate with this file.    Attribute "system". Specified system file.    Attribute "volume label". In old version of MSDOS used for specified volume laben, now it can be used for long filenames. And must be 0 for compatibles.    Attribute "directory". When value is 1, means that this file is directory.    Attribute "archive". This bite sets in 1 when DSS writing in this file. It can be used in backup utilities for detect changed files.  File handle     When any file are opened, DSS build File Control Block in DSS working areas.    The Handle (and assigned file) identified by number which returned DSS to program after file opening and used it in all further DSS calls. In other words, when file is opening, the program informsDSS his name and has taken back file handle. Which used in further file operations.    All necessary information for working with file are placed in DSS working areas.
2. Identification of system functions
00h (00) VERSION (Version of DSS)  input:  C - 00h  output:  D - version number E - modification  The function return version number of DSS.
3. Disk devices functions
01h (01) CHDISK (Change current disk)  input:  A - disk number (0-A,1-B...) C - 01h  output:  A - error code, if CF=1 A - number of disks, if CF=0  The function changes current disk device.   02h (02) CURDISK (Current disk number)  input:  C - 02h  output:  A - current disk number (0-A,1-B...)  The function returns number of current disk device.   03h (03) DSKINFO (Disk information)  input:  A - disk number (0-A,1-B...0FFh-current) C - 03h  output:  A - error code, if CF=1 A - sectors per cluster, if CF=0 HL - clusters per disk DE - free clusters BC - bytes per sector  The function returns information about disk device (capacity and free space).  for example: 
	LD	C,03h		;Function DSKINFO
	LD	A,0FFh		;Information about current disk
	RST	10h		;Execution of function
	LD	A,D		;There is a free
	OR	E		;space?
	JR	Z,NO_SPACE	;No, the disk is completely filled
09h (09) BOOTDSK (Number of boot disk)  input:  C - 09h B = 0  output:  A - number of boot disk (0-A,1-B...)  The function returns number of boot disk device whence was loaded DSS.
