INT 13
Encyclopedia
INT 13H or INT 19 is shorthand for BIOS interrupt call
13hex
, the 20th interrupt vector
in an x86-based computer system. The BIOS
typically sets up a real mode
interrupt handler
at this vector that provides sector-based hard disk and floppy disk read and write services using cylinder-head-sector
(CHS) addressing.
INT
is an x86 instruction that triggers a software interrupt, and 13hex vector passed to the instruction (interrupts start at zero, and are labeled with hexadecimal
values).
operating systems, such as MS-DOS
, calling INT 0x13 would jump into the computer's BIOS code for low level disk services, which would carry out sector-based disk read or write operations for the program. In MS-DOS it serves as a foundation for higher-level MS-DOS API
(INT 21h) functions which deal with file system
access.
Under protected mode
operating systems, such as Microsoft Windows NT derivatives (e.g. NT4, 2000, XP, and Server 2003) and Linux
with dosemu
, the OS intercepts the call and passes it to the operating system's native disk I/O mechanism. Windows 9x
and Windows for Workgroups 3.11 also bypass BIOS routines when using 32-bit File Access
.
The original BIOS real-mode INT 0x13 interface supports drives of sizes up to about 504 MB using what is commonly referred to as physical CHS addressing. This limit originates from the hardware interface of the x86 disk hardware. The BIOS used the cylinder-head-sector
(CHS) address given in the INT 0x13 call, and transmitted it directly to the hardware interface.
This interface was later extended to support addressing of up to exactly 8064 MB using what is commonly referred to as logical CHS addressing. This limit originates from a combination of the register value based calling convention used in the INT 0x13 interface, and the goal of maintaining backward compatibility. There were originally a number of BIOSes that offered incompatible versions of this interface, but eventually the computer industry standardized on the interface developed in the Microid Research ("MR BIOS") in 1989. This limit uses 1024 cylinders, 256 heads, 63 sectors, and 512 byte blocks, giving roughly 7.875 GB of addressing (1024 * 256 * 63 * 512).
To support even larger addressing modes, an interface known as 'INT13h Extensions was introduced by Western Digital
and Phoenix Technologies
as part of BIOS Enhanced Disk Drive Services (EDD) standard. It uses 64-bit logical block addressing
(LBA) which allows addressing up to 8 ZiB
(the drive can also support 28-bit or 48-bit LBA which allows up to 128 GiB
or 128 PiB
respectively, assuming a 512-byte sector/block size). This is a packet interface, because it uses a pointer to a packet of information rather than the register based calling convention of the original INT 13 interface. This packet is a data structure that contains an interface version, data size, and LBAs.
All versions of MS-DOS
, including MS-DOS 7, and Windows 95
contain a bug that prevents booting hard disks with 256 heads (register value 0xFF), so many modern BIOS maps the drives to have at most 255 heads. Also some cache drivers will flush their buffers when detecting that MS-DOS is bypassed by applications that directly issues INT 13h requests.
AMI BIOSes from around 1990-1991 trash word unaligned buffers. Some MS-DOS and TSR
programs clobber interrupt enabling and registers so PC-DOS
and MS-DOS
install their own filters to prevent this.
If the second column is empty then the function may be used both for floppy and hard disk.
Results:
$Bit 7=0 for floppy drive, bit 7=1 for fixed drive
Results:
Results:
Remarks:
Register CX contains both the cylinder number (10 bit
s, possible values are 0 to 1023)
and the sector number (6 bits, possible values are 1 to 63):
CX = ---CH--- ---CL---
cylinder : 76543210 98
sector : 543210
Examples of translation:
CX := ( ( cylinder and 255 ) shl 8 ) or ( ( cylinder and 768 ) shr 2 ) or sector;
cylinder := ( (CX and 0xFF00) shr 8 ) or ( (CX and 0xC0) shl 2)
sector := CX and 63;
Addressing of Buffer should guarantee that the complete buffer is inside the given segment,
i.e. ( BX + size_of_buffer ) <= 10000h.
Otherwise the interrupt may fail with some BIOS or hardware versions.
Example: Assume you want to read 16 sectors (= 2000h byte
s) and your buffer starts
at memory address 4FF00h. Utilizing memory segmentation, there are different ways to calculate the register values, e.g.:
ES = segment = 4F00h
BX = offset = 0F00h
sum = memory address = 4FF00h
would be a good choice because 0F00h + 2000h = 2F00h <= 10000h
ES = segment = 4000h
BX = offset = FF00h
sum = memory address = 4FF00h
would not be a good choice because FF00h + 2000h = 11F00h > 10000h
Function 02h of interrupt 13h may only read sectors of the first 16,450,560 sectors
of your hard drive, to read sectors beyond the 8 GB limit you should use function 42h
of Int 13h Extensions. Another alternate may be DOS interrupt 25h which reads sectors
within a partition.
Results:
Results:
$4-byte address field (applies to PC/XT 286,AT, PS/1 and PS/2)
Results:
Results:
Results:
Results:
Remarks:
Logical values of function 08h may/should differ from physical CHS values of function 48h.
Result register CX contains both cylinders and sector/track values, see remark of function 02h.
Results:
instead of only 512. The last 4 bytes contains the Error Correction Code ECC, a checksum of sector data.
Results:
Results:
Results:
Remark: Physical CHS values of function 48h may/should differ from logical values of function 08h.
BIOS interrupt call
BIOS interrupt calls are a facility that DOS programs and some other software, such as boot loaders, use to invoke the facilities of the Basic Input/Output System...
13hex
Hexadecimal
In mathematics and computer science, hexadecimal is a positional numeral system with a radix, or base, of 16. It uses sixteen distinct symbols, most often the symbols 0–9 to represent values zero to nine, and A, B, C, D, E, F to represent values ten to fifteen...
, the 20th interrupt vector
Interrupt vector
An interrupt vector is the memory address of an interrupt handler, or an index into an array called an interrupt vector table that contains the memory addresses of interrupt handlers...
in an x86-based computer system. The BIOS
BIOS
In IBM PC compatible computers, the basic input/output system , also known as the System BIOS or ROM BIOS , is a de facto standard defining a firmware interface....
typically sets up a real mode
Real mode
Real mode, also called real address mode, is an operating mode of 80286 and later x86-compatible CPUs. Real mode is characterized by a 20 bit segmented memory address space and unlimited direct software access to all memory, I/O addresses and peripheral hardware...
interrupt handler
Interrupt handler
An interrupt handler, also known as an interrupt service routine , is a callback subroutine in microcontroller firmware, operating system or device driver whose execution is triggered by the reception of an interrupt...
at this vector that provides sector-based hard disk and floppy disk read and write services using cylinder-head-sector
Cylinder-head-sector
Cylinder-head-sector, also known as CHS, was an early method for giving addresses to each physical block of data on a hard disk drive. In the case of floppy drives, for which the same exact diskette medium can be truly low-level formatted to different capacities, this is still true.Though CHS...
(CHS) addressing.
INT
INT (x86 instruction)
INT is an assembly language instruction for x86 processors that generates a software interrupt. It takes the interrupt number formatted as a byte value.When written in assembly language, the instruction is written like this:...
is an x86 instruction that triggers a software interrupt, and 13hex vector passed to the instruction (interrupts start at zero, and are labeled with hexadecimal
Hexadecimal
In mathematics and computer science, hexadecimal is a positional numeral system with a radix, or base, of 16. It uses sixteen distinct symbols, most often the symbols 0–9 to represent values zero to nine, and A, B, C, D, E, F to represent values ten to fifteen...
values).
Overview
Under real modeReal mode
Real mode, also called real address mode, is an operating mode of 80286 and later x86-compatible CPUs. Real mode is characterized by a 20 bit segmented memory address space and unlimited direct software access to all memory, I/O addresses and peripheral hardware...
operating systems, such as MS-DOS
MS-DOS
MS-DOS is an operating system for x86-based personal computers. It was the most commonly used member of the DOS family of operating systems, and was the main operating system for IBM PC compatible personal computers during the 1980s to the mid 1990s, until it was gradually superseded by operating...
, calling INT 0x13 would jump into the computer's BIOS code for low level disk services, which would carry out sector-based disk read or write operations for the program. In MS-DOS it serves as a foundation for higher-level MS-DOS API
MS-DOS API
The MS-DOS API is an API used originally in MS-DOS/PC-DOS, and later by other DOS systems. Most calls to the DOS API invoke software interrupt 21h . By calling INT 21h with a subfunction number in the AH processor register and other parameters in other registers, one invokes various DOS services...
(INT 21h) functions which deal with file system
File system
A file system is a means to organize data expected to be retained after a program terminates by providing procedures to store, retrieve and update data, as well as manage the available space on the device which contain it. A file system organizes data in an efficient manner and is tuned to the...
access.
Under protected mode
Protected mode
In computing, protected mode, also called protected virtual address mode, is an operational mode of x86-compatible central processing units...
operating systems, such as Microsoft Windows NT derivatives (e.g. NT4, 2000, XP, and Server 2003) and Linux
Linux
Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...
with dosemu
DOSEMU
DOSEMU, alternatively rendered dosemu, is a compatibility layer software package that enables MS-DOS systems, DOS clones such as FreeDOS, and DOS software to run under Linux on x86-based PCs ....
, the OS intercepts the call and passes it to the operating system's native disk I/O mechanism. Windows 9x
Windows 9x
Windows 9x is a generic term referring to a series of Microsoft Windows computer operating systems produced since 1995, which were based on the original and later modified Windows 95 kernel...
and Windows for Workgroups 3.11 also bypass BIOS routines when using 32-bit File Access
32-bit File Access
32-bit file access refers to the higher performance, protected mode disk caching method introduced in Windows for Workgroups 3.11, which replaced SmartDrive . It bypassed MS-DOS and directly accessed the disk, either via the BIOS or 32-bit disk access...
.
The original BIOS real-mode INT 0x13 interface supports drives of sizes up to about 504 MB using what is commonly referred to as physical CHS addressing. This limit originates from the hardware interface of the x86 disk hardware. The BIOS used the cylinder-head-sector
Cylinder-head-sector
Cylinder-head-sector, also known as CHS, was an early method for giving addresses to each physical block of data on a hard disk drive. In the case of floppy drives, for which the same exact diskette medium can be truly low-level formatted to different capacities, this is still true.Though CHS...
(CHS) address given in the INT 0x13 call, and transmitted it directly to the hardware interface.
This interface was later extended to support addressing of up to exactly 8064 MB using what is commonly referred to as logical CHS addressing. This limit originates from a combination of the register value based calling convention used in the INT 0x13 interface, and the goal of maintaining backward compatibility. There were originally a number of BIOSes that offered incompatible versions of this interface, but eventually the computer industry standardized on the interface developed in the Microid Research ("MR BIOS") in 1989. This limit uses 1024 cylinders, 256 heads, 63 sectors, and 512 byte blocks, giving roughly 7.875 GB of addressing (1024 * 256 * 63 * 512).
To support even larger addressing modes, an interface known as 'INT13h Extensions was introduced by Western Digital
Western Digital
Western Digital Corporation is one of the largest computer hard disk drive manufacturers in the world. It has a long history in the electronics industry as an integrated circuit maker and a storage products company. Western Digital was founded on April 23, 1970 by Alvin B...
and Phoenix Technologies
Phoenix Technologies
Phoenix Technologies Ltd designs, develops and supports core system software for personal computers and other computing devices. Phoenix's products — commonly referred to as BIOS or firmware — support and enable the compatibility, connectivity, security and management of the various components and...
as part of BIOS Enhanced Disk Drive Services (EDD) standard. It uses 64-bit logical block addressing
Logical block addressing
Logical block addressing is a common scheme used for specifying the location of blocks of data stored on computer storage devices, generally secondary storage systems such as hard disks....
(LBA) which allows addressing up to 8 ZiB
Zebibyte
The zebibyte is a standards-based binary multiple of the byte, a unit of digital information storage. The zebibyte unit symbol is ZiB.1 zebibyte = 270 bytes = = 1,024 exbibytes...
(the drive can also support 28-bit or 48-bit LBA which allows up to 128 GiB
Gibibyte
The gibibyte is a standards-based binary multiple of the byte, a unit of digital information storage. The gibibyte unit symbol is GiB....
or 128 PiB
Pebibyte
The pebibyte is a standards-based binary multiple of the byte, a unit of digital information storage. The pebibyte unit symbol is PiB....
respectively, assuming a 512-byte sector/block size). This is a packet interface, because it uses a pointer to a packet of information rather than the register based calling convention of the original INT 13 interface. This packet is a data structure that contains an interface version, data size, and LBAs.
All versions of MS-DOS
MS-DOS
MS-DOS is an operating system for x86-based personal computers. It was the most commonly used member of the DOS family of operating systems, and was the main operating system for IBM PC compatible personal computers during the 1980s to the mid 1990s, until it was gradually superseded by operating...
, including MS-DOS 7, and Windows 95
Windows 95
Windows 95 is a consumer-oriented graphical user interface-based operating system. It was released on August 24, 1995 by Microsoft, and was a significant progression from the company's previous Windows products...
contain a bug that prevents booting hard disks with 256 heads (register value 0xFF), so many modern BIOS maps the drives to have at most 255 heads. Also some cache drivers will flush their buffers when detecting that MS-DOS is bypassed by applications that directly issues INT 13h requests.
AMI BIOSes from around 1990-1991 trash word unaligned buffers. Some MS-DOS and TSR
Terminate and Stay Resident
Terminate and Stay Resident is a computer system call in DOS computer operating systems that returns control to the system as if the program has quit, but keeps the program in memory...
programs clobber interrupt enabling and registers so PC-DOS
PC-DOS
IBM PC DOS is a DOS system for the IBM Personal Computer and compatibles, manufactured and sold by IBM from the 1980s to the 2000s....
and MS-DOS
MS-DOS
MS-DOS is an operating system for x86-based personal computers. It was the most commonly used member of the DOS family of operating systems, and was the main operating system for IBM PC compatible personal computers during the 1980s to the mid 1990s, until it was gradually superseded by operating...
install their own filters to prevent this.
Drive Table
| DL = 00h | 1st floppy disk ( "drive A:" ) |
| DL = 01h | 2nd floppy disk ( "drive B:" ) |
| DL = 80h | 1st hard disk |
| DL = 81h | 2nd hard disk |
Function Table
| AH = 00h | Reset Disk Drives | |
| AH = 01h | Get Status of Last Drive Operation | |
| AH = 02h | Read Sectors From Drive | |
| AH = 03h | Write Sectors To Drive | |
| AH = 04h | Verify Sectors | |
| AH = 05h | Format Track | |
| AH = 06h | Format Track Set Bad Sector Flags | |
| AH = 07h | Format Drive starting at Track | |
| AH = 08h | Read Drive Parameters | |
| AH = 09h | HD | Initialize Disk Controller |
| AH = 0Ah | HD | Read Long Sectors From Drive |
| AH = 0Bh | HD | Write Long Sectors To Drive |
| AH = 0Ch | HD | Move Drive Head To Cylinder |
| AH = 0Dh | HD | Reset Disk Drives |
| AH = 0Eh | PS/2 | Controller Read Test |
| AH = 0Fh | PS/2 | Controller Write Test |
| AH = 10h | HD | Test Whether Drive Is Ready |
| AH = 11h | HD | Recalibrate Drive |
| AH = 12h | PS/2 | Controller RAM Test |
| AH = 13h | PS/2 | Drive Test |
| AH = 14h | HD | Controller Diagnostic |
| AH = 15h | Read Drive Type | |
| AH = 16h | FD | Detect Media Change |
| AH = 17h | FD | Set Media Type For Format ( used by DOS versions <= 3.1 ) |
| AH = 18h | FD | Set Media Type For Format ( used by DOS versions >= 3.2 ) |
| AH = 19h | Park Heads | |
| AH = 41h | EXT | Test Whether Extensions Are Available |
| AH = 42h | EXT | Read Sectors From Drive |
| AH = 43h | EXT | Write Sectors To Drive |
| AH = 44h | EXT | Verify Sectors |
| AH = 45h | EXT | Lock/Unlock Drive |
| AH = 46h | EXT | Eject Drive |
| AH = 47h | EXT | Move Drive Head To Sector |
| AH = 48h | EXT | Read Drive Parameters |
| AH = 49h | EXT | Detect Media Change |
If the second column is empty then the function may be used both for floppy and hard disk.
- FD: for floppy disk only.
- HD: for hard disk only.
- PS/2: for hard disk on PS/2 system only.
- EXT: part of the Int 13h Extensions which were written in the 1990s to support hard drives with more than 8 GBGigabyteThe gigabyte is a multiple of the unit byte for digital information storage. The prefix giga means 109 in the International System of Units , therefore 1 gigabyte is...
.
INT 13h AH=00h: Reset Disk Drive
Parameters:| AH | 00h |
| DL | Drive |
Results:
| CF | Set on error |
INT 13h AH=01h: Get Status of Last Drive Operation
Parameters:| AH | 01h |
| DL | Drive$ |
$Bit 7=0 for floppy drive, bit 7=1 for fixed drive
Results:
| AL | Return Code
|
| CF | Set On Error, Clear If No Error |
INT 13h AH=02h: Read Sectors From Drive
Parameters:| AH | 02h |
| AL | Sectors To Read Count |
| CH | Track |
| CL | Sector |
| DH | Head |
| DL | Drive |
| ES:BX | Buffer Address Pointer |
Results:
| CF | Set On Error, Clear If No Error |
| AH | Return Code |
| AL | Actual Sectors Read Count |
Remarks:
Register CX contains both the cylinder number (10 bit
Bit
A bit is the basic unit of information in computing and telecommunications; it is the amount of information stored by a digital device or other physical system that exists in one of two possible distinct states...
s, possible values are 0 to 1023)
and the sector number (6 bits, possible values are 1 to 63):
CX = ---CH--- ---CL---
cylinder : 76543210 98
sector : 543210
Examples of translation:
CX := ( ( cylinder and 255 ) shl 8 ) or ( ( cylinder and 768 ) shr 2 ) or sector;
cylinder := ( (CX and 0xFF00) shr 8 ) or ( (CX and 0xC0) shl 2)
sector := CX and 63;
Addressing of Buffer should guarantee that the complete buffer is inside the given segment,
i.e. ( BX + size_of_buffer ) <= 10000h.
Otherwise the interrupt may fail with some BIOS or hardware versions.
Example: Assume you want to read 16 sectors (= 2000h byte
Byte
The byte is a unit of digital information in computing and telecommunications that most commonly consists of eight bits. Historically, a byte was the number of bits used to encode a single character of text in a computer and for this reason it is the basic addressable element in many computer...
s) and your buffer starts
at memory address 4FF00h. Utilizing memory segmentation, there are different ways to calculate the register values, e.g.:
ES = segment = 4F00h
BX = offset = 0F00h
sum = memory address = 4FF00h
would be a good choice because 0F00h + 2000h = 2F00h <= 10000h
ES = segment = 4000h
BX = offset = FF00h
sum = memory address = 4FF00h
would not be a good choice because FF00h + 2000h = 11F00h > 10000h
Function 02h of interrupt 13h may only read sectors of the first 16,450,560 sectors
of your hard drive, to read sectors beyond the 8 GB limit you should use function 42h
of Int 13h Extensions. Another alternate may be DOS interrupt 25h which reads sectors
within a partition.
INT 13h AH=03h: Write Sectors To Drive
Parameters:| AH | 03h |
| AL | Sectors To Write Count |
| CH | Track |
| CL | Sector |
| DH | Head |
| DL | Drive |
| ES:BX | Buffer Address Pointer |
Results:
| CF | Set On Error, Clear If No Error |
| AH | Return Code |
| AL | Actual Sectors Written Count |
INT 13h AH=04h: Verify Sectors From Drive
Parameters:| AH | 04h |
| AL | Sectors To Verify Count |
| CH | Track |
| CL | Sector |
| DH | Head |
| DL | Drive |
| ES:BX | Buffer Address Pointer |
Results:
| CF | Set On Error, Clear If No Error |
| AH | Return Code |
| AL | Actual Sectors Verified Count |
INT 13h AH=05h: Format Track
Parameters:| AH | 05h |
| AL | Sectors To Format Count |
| CH | Track |
| CL | Sector |
| DH | Head |
| DL | Drive |
| ES:BX | Buffer Address Pointer$ |
$4-byte address field (applies to PC/XT 286,AT, PS/1 and PS/2)
| Byte | Meaning | Allowable Values |
| 1 | Track | |
| 2 | Head | |
| 3 | Sector | |
| 4 | Bytes/Sector | 0=128, 1-256, 2-512, 3-1024 |
Results:
| CF | Set On Error, Clear If No Error |
| AH | Return Code |
INT 13h AH=06h: Format Track Set Bad Sector Flags
Parameters:| AH | 06h |
| AL | Interleave |
| CH | Track |
| CL | Sector |
| DH | Head |
| DL | Drive |
Results:
| CF | Set On Error, Clear If No Error |
| AH | Return Code |
INT 13h AH=07h: Format Track Set Bad Sector Flags
Parameters:| AH | 07h |
| AL | Interleave |
| CH | Track |
| CL | Sector |
| DH | Head |
| DL | Drive |
Results:
| CF | Set On Error, Clear If No Error |
| AH | Return Code |
INT 13h AH=08h: Read Drive Parameters
Parameters:| Registers | |
|---|---|
| AH | 08h = function number for read_drive_parameters |
| DL | drive index (e.g. 1st HDD = 80h) |
| ES:DI | set to 0000h:0000h to workaround some buggy BIOS |
Results:
| CF | Set On Error, Clear If No Error |
| AH | Return Code |
| DL | number of hard disk drives |
| DH | logical last index of heads = number_of - 1 (because index starts with 0) |
| CX | [7:6] [15:8] logical last index of cylinders = number_of - 1 (because index starts ) [5:0] logical last index of sectors per track = number_of (because index starts with 1) |
| BL | drive type (only AT/PS2 floppies) |
| ES:DI | pointer to drive parameter table (only for floppies) |
Remarks:
Logical values of function 08h may/should differ from physical CHS values of function 48h.
Result register CX contains both cylinders and sector/track values, see remark of function 02h.
INT 13h AH=09h: Init Drive Pair Characteristics
Parameters:| AH | 09h |
| DL | Drive |
Results:
| CF | Set On Error, Clear If No Error |
| AH | Return Code |
INT 13h AH=0Ah: Read Long Sectors From Drive
The only difference between this function and function 02h (see above) is that function 0Ah reads 516 bytes per sectorinstead of only 512. The last 4 bytes contains the Error Correction Code ECC, a checksum of sector data.
INT 13h AH=41h: Check Extensions Present
Parameters:| Registers | |
|---|---|
| AH | 41h = function number for extensions check |
| DL | drive index (e.g. 1st HDD = 80h) |
| BX | 55AAh |
Results:
| CF | Set On Not Present, Clear If Present |
| AH | Error Code or Major Version Number |
| BX | AA55h |
| CX | Interface support bitmask: 1 - Device Access using the packet structure 2 - Drive Locking and Ejecting 4 - Enhanced Disk Drive Support (EDD) |
INT 13h AH=42h: Extended Read Sectors From Drive
Parameters:| Registers | |
|---|---|
| AH | 42h = function number for extended read |
| DL | drive index (e.g. 1st HDD = 80h) |
| DS:SI | segment:offset pointer to the DAP, see below |
| DAP : Disk Address Packet | ||
|---|---|---|
| offset range | size | description |
| 00h | 1 byte | size of DAP = 16 = 10h |
| 01h | 1 byte | unused, should be zero |
| 02h..03h | 2 bytes | number of sectors to be read, (some Phoenix BIOSes are limited to a maximum of 127 sectors) |
| 04h..07h | 4 bytes | segment:offset pointer to the memory buffer to which sectors will be transferred (note that x86 is little-endian: if declaring the segment and offset separately, the offset must be declared before the segment) |
| 08h..0Fh | 8 bytes | absolute number of the start of the sectors to be read (1st sector of drive has number 0) |
Results:
| CF | Set On Error, Clear If No Error |
| AH | Return Code |
INT 13h AH=48h: Extended Read Drive Parameters
Parameters:| Registers | |
|---|---|
| AH | 48h = function number for extended_read_drive_parameters |
| DL | drive index (e.g. 1st HDD = 80h) |
| DS:SI | segment:offset pointer to Result Buffer, see below |
| Result Buffer | ||
|---|---|---|
| offset range | size | description |
| 00h..01h | 2 bytes | size of Result Buffer = 30 = 1Eh |
| 02h..03h | 2 bytes | information flags |
| 04h..07h | 4 bytes | physical number of cylinders = last index + 1 (because index starts with 0) |
| 08h..0Bh | 4 bytes | physical number of heads = last index + 1 (because index starts with 0) |
| 0Ch..0Fh | 4 bytes | physical number of sectors per track = last index (because index starts with 1) |
| 10h..17h | 8 bytes | absolute number of sectors = last index + 1 (because index starts with 0) |
| 18h..19h | 2 bytes | bytes per sector |
| 1Ah..1Dh | 4 bytes | optional pointer to Enhanced Disk Drive (EDD) configuration parameters which may be used for subsequent interrupt 13h Extension calls (if supported) |
Results:
| CF | Set On Error, Clear If No Error |
| AH | Return Code |
Remark: Physical CHS values of function 48h may/should differ from logical values of function 08h.
See also
- INT 10H
- BIOS interrupt callBIOS interrupt callBIOS interrupt calls are a facility that DOS programs and some other software, such as boot loaders, use to invoke the facilities of the Basic Input/Output System...
- Cylinder-head-sectorCylinder-head-sectorCylinder-head-sector, also known as CHS, was an early method for giving addresses to each physical block of data on a hard disk drive. In the case of floppy drives, for which the same exact diskette medium can be truly low-level formatted to different capacities, this is still true.Though CHS...
- INT (x86 instruction)INT (x86 instruction)INT is an assembly language instruction for x86 processors that generates a software interrupt. It takes the interrupt number formatted as a byte value.When written in assembly language, the instruction is written like this:...
- DPMI (DOS Protected Mode Interface)