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June 23, 2010 T13/2132-D Revision 3
Working Draft Enhanced Disk Drive - 4 (EDD-4) 17
6.3 Removable Media
The distinction between "removable" disks numbered 00h through 7Fh and "fixed" disks numbered 80h through
FFh differs from conventional INT 13h functions. Devices numbered 0 through 7Fh are not changed. They
follow conventional INT 13h standards for floppy disk operation. Devices numbered 80h through FFh include
traditional fixed disks, and now also include removable media devices that support media change notification as
well as software locking and unlocking capabilities. Functions in this standard support these devices. The
values returned in the AL register upon completion of an INT 13h Function are vendor specific. Table 10
describes the return codes that are supported for removable media devices.
6.4 INT 13h Interface Subsets
6.4.1 Overview
It is permissible for BIOS to support only certain subsets of the INT 13h extensions. These subsets are defined
in this standard. If a subset is supported then all functions within that subset shall be supported. The supported
subsets shall be determined via the Check Extensions Present function. If a function is not supported and that
function is subsequently invoked; then the function rejects the request with CF = 1b and AH = 01h. There are
three subsets defined. At least one of these shall be supported.
NOTE 1 — Conventional INT 13h may be used for media accessing if the Fixed Disk Access Subset
is not present.
6.4.2 Fixed Disk Access Subset
These functions support basic access to devices using the device address packet structure (see table 11).
Table 10 — Removable Media Return Codes
Return Code Description
B0h Media Not Locked In Device
B1h
Media Locked In Device
B2h
Media Not Removable
B3h
Media In Use
B4h
Lock Count Exceeded
B5h
Valid Eject Request Failed
B6h
Media Present but Read Protected
Table 11 — Fixed Disk Access
Function Code
Check Extensions Present (see 8.14) 41h
Extended Read (see 8.15) 42h
Extended Write (see 8.16) 43h
Verify Sectors (see 8.17) 44h
Obsolete 47h
Get Device Parameters (see 8.20) 48h