System for reconfiguring a boot device by swapping the logical device number of a user selected boot drive to a currently configured boot drive

[0002] 1. Field of the Invention

[0003] The present invention relates generally to computer disk boot systems, and more particularly to an apparatus and method of configuring and booting disk drives in a computer system.

[0004] 2. Description of the Related Art

[0005] The Basic Input/Output System (BIOS) of a computer contains the drivers, or software interfaces for hardware devices of the computer. These devices include the keyboard, the display, the printer, auxiliary devices such as the serial port, the computer's clock and the boot disk device. Part of the BIOS is built into each computer by the computer's manufacturer. This part of the BIOS is called the resident BIOS. It is also known as the Read Only Memory (ROM) BIOS because it is contained in ROM chips located on the computer system board. The ROM BIOS serves as an interface with the computer hardware; it controls the hardware devices installed in a computer. It also presents a standardized interface to application and operating system software.

[0006] The second part of the BIOS is nonresident; it is read into random access memory (RAM) from disk when the computer boots. The boot operation itself performs two functions. It runs a power-on self test (POST) of the computer and searches disk drives for an operating system. When these functions are complete, the boot operation begins the process of reading the operating system files from disk and copying them to a location in the computer's RAM. The Master Boot Record is read first, followed by the Disk Operating System (DOS) Boot Record. After loading the disk BIOS, the DOS Boot Record is no longer required and is over written in RAM by other code.

[0007] BIOS disk services are typically invoked through the use of an interrupt (INT 13hand/or 40h) and are selected by loading the service number into a dedicated register in the processor. In particular, hard drives are typically invoked through the use of INT 13h, while BIOS-controlled floppy drives are invoked through the use of INT 40h. Disk drives are identified by a zero-based number provided in another dedicated register, with the highest order bit set to 1 to indicate a hard disk. Thus, the first floppy disk drive in the computer is identified by drive number 00hand the first hard disk drive is designated by drive number 80h. The BIOS uses a set of descriptive parameter tables called disk-base tables to gain information regarding the capabilities of the disk controller hardware and the disk media. During start up, the BIOS associates an appropriate disk-based table with each hard disk drive.

[0008] There has been developed a disk process in which a hard disk drive may be installed in the order specified by the user. Each hard disk drive is configured by assigning its respective interface routine to a location on the INT 13hchain. Once the drive has been configured, it is assigned a logical drive number from 80hto 9Fh. The first drive that is installed is configured as 80h, the second as 81h, etc. The operating system subsequently recognizes drive 80has the boot device.

[0009] Currently, once the devices have been installed in the INT 13hchain, the logical drive number cannot be altered. While this ensures that the boot process will commence from a specific drive, it poses a problem if the user determines, prior to booting, that the boot process should commence from another device. In addition, even if the user were to reconfigure the boot process to commence from another logical drive, such as logical drive 81h, the operating system would override such an instruction and would commence to boot from drive 80h.

[0010] Accordingly, there is a need in the technology for an apparatus and method for facilitating the selection of a boot device from a plurality of disk drives that are installed on a computer system.

[0011] The present invention is an apparatus and method for specifying operation of a boot device in a processor-based system. The apparatus comprises a memory for storing instruction sequences by which the processor-based system is processed and a processor for executing the stored instruction sequences. The stored instruction sequences cause the processor to: (a) determine if a boot process should proceed from a currently specified drive; (b) if not, specify a drive from which the boot process will proceed; and (c) initiate the boot process.

[0012] FIG. 1 is a system block diagram of an exemplary processor system in which the apparatus and method of the present invention is used.

[0013] FIG. 2 illustrates one embodiment of an INT 13htemplate that is utilized by the present invention.

[0014] FIG. 3 is a flow chart illustrating one embodiment of the boot drive selection and configuration process provided in accordance with the principles of the present invention.

[0015] FIGS. 4A and 4B are flowcharts which illustrate one embodiment of the boot drive specification and configuration process 106 of FIG. 3.

[0016] The present embodiment is described in reference to a processor system 10. FIG. 1 illustrates an exemplary processor system 10 which implements the processes of the present invention. The processor system 10 comprises a processor 12 and a memory module 14. The memory module 14 includes random access memory (RAM) 16 and read-only memory (ROM) 18. In one embodiment, the memory module 14 also includes a main memory or a dynamic random access memory (DRAM). The processing system 10 also comprises a controller circuit 20 such as a SCSI controller. The processor 12, memory module 14 and controller circuit 20 are coupled to a system bus 22. The processor system 10 also comprises hardware devices 24 and various I/O and peripheral devices 26 which are coupled to the system bus 22. Examples of the hardware devices 24 include, but are not limited to a floppy drive, a hard drive, a PCMCIA card, a CD-ROM drive, a network interface, a tape drive a Universal Serial Bus boot device, an IDE drive and a SCSI drive. Examples of the I/O devices 26 include a keyboard, a mouse and a console.

[0017] Stored in ROM 18 is a Basic Input/Output System (“BIOS”) program. The BIOS program is a collection of drivers, or software interfaces for hardware devices such as the console (keyboard and display), a generic printer, the auxiliary device (serial port), the computer's clock and the boot disk device. The BIOS is typically embedded in programmable, read only memory (PROM). Often, the BIOS functions themselves are actually copied from PROM into RAM 16, taking advantage of the faster access times of RAM 16. This is known as “shadowing” the BIOS because two copies of BIOS results: one in PROM (which will no longer be used) and the other in RAM 16. The portion of RAM 16 which stores the BIOS is known as the BIOS shadow space. The BIOS, when executed by the processor 12, configures the processor 12 to execute POST operations and to initialize the various hardware devices 24 and the miscellaneous I/O and peripheral devices 26.

[0018] Located in memory module 14 is a boot connection vector (BCV) device record which contains the identity of the hardware devices or BCV devices (such as hard disk drives) that are coupled to the system bus 20. FIG. 1 also illustrates one embodiment of the BCV device control system as utilized by the present invention. As shown, a first plurality of the BCV devices are controlled by the BIOS routine while a second plurality of the BCV devices are controlled by the controller circuit 20. The BCV device record, which includes a list of the BIOS-controlled devices and a list of the non-BIOS controlled BCV devices, is created during initialization of the processor system 10, and stored in shadow RAM. The BCV record further comprises the logical device numbers and the entry points of the BCV devices installed on the system 10.

[0019] Associated with each BIOS-controlled BCV device is an interrupt INT 13htemplate structure stored in memory module 14, which contains the address offsets of the interrupt (INT) 13hhandler, the disk parameter table, the physical drive, the logical drive, the INT 13hprotocol and a model number of a corresponding BIOS-controlled BCV device. FIG. 2 illustrates one embodiment of an INT 13htemplate that is utilized by the present invention. The INT 13htemplate also includes the physical and logical drive number of the corresponding BIOS-controlled hardware device 24. Thus, there is an INT 13htemplate structure for each BIOS-controlled hardware device 24. In alternate embodiments, an INT 40htemplate structure similar to the interrupt INT 13htemplate structure, may be used to implement the present invention in addressing BIOS-controlled floppy disk drives.

[0020] The present invention facilitates the selection and configuration of a hardware devices or a BCV device (such as a hard disk drive) from a plurality of hardware device or BCV devices 24 (such as a plurality of hard disk drives) that are installed on the processor system 10. FIG. 3 is a flow chart illustrating one embodiment of the boot drive selection and configuration process provided in accordance with the principles of the present invention. Beginning from a start state, the process 100 proceeds to process block 110, where it conducts power on self test (POST), initialization and installation procedures. At this juncture, the hardware devices 24 and the I/O and peripheral devices 26 are initialized and installed. Hardware devices 24 that are configured to be controlled by BIOS are installed on the INT 13htemplate structure. The boot connection vector (BCV) device record is also created at this juncture.

[0021] The process 100 then proceeds to decision block 120, where it determines if the boot process should proceed from a currently specified drive. If not, the process 100 proceeds to process block 130, where the user is prompted to specify the drive from which the boot process should proceed. The process 100 then configures the specified drive for the booting process. The process 100 then advances to process block 140, where it initiates the booting process. If, at decision block 120, the process 100 determines that the boot process should proceed from the currently specified drive, the process would proceed directly to process block 140. Upon completing the boot process, the process 100 terminates.

[0022] FIGS. 4A and 4B are flowcharts which illustrate one embodiment of the boot drive specification and configuration process 130 of FIG. 3. Beginning from a start state, the process 130 proceeds to process block 205 where it prompts the user to specify the drive from which the operating system will be booted. The process 130 then proceeds to process block 210, where it saves the logical drive number of the specified drive. The process 130 then determines if the specified drive is BIOS-controlled, as shown in decision block 215. This is accomplished by scanning the BIOS-controlled INT 13htemplate structures, such as that shown in FIG. 2. If the specified drive is not BIOS-controlled (that is, the logical drive number of the specified drive was not found on any of the BIOS-controlled INT 13htemplate structures), the process 130 proceeds to process block 220, where it calls the BCV entry routine to change the logical drive number of the specified drive to 80h. The process 130 then proceeds to process block 230. If however, the logical drive number of the specified drive was found on one of the BIOS-controlled INT 13htemplate structures, the process 130 proceeds to process block 225, where it changes the logical drive number of the specified drive to 80hin the corresponding INT 13htemplate structure. The process 130 then proceeds to process block 230.

[0023] At process block 230, the process 130 scans the BIOS-controlled INT 13htemplate structure for logical drive 80h. It then proceeds to decision block 235, where it determines if logical drive 80hwas found in the BIOS-controlled INT 13htemplate structure. If not, the process proceeds to process block 240, where it determines that the currently configured drive 80his not BIOS-controlled. The process 130 then proceeds to call the BCV routine to hang the logical drive number for the currently configured drive 80hto the logical drive number of the specified drive. The process then returns to the main process. However, if the drive 80has found on one of the INT 13htemplate structures, the process proceeds to process block 245, where it copies the saved logical drive number of the specified drive to the INT 13htemplate of the currently configured drive 80h. The process 130 then returns to the main process.

[0024] The present invention thus provides an apparatus and method for facilitating the selection of a boot device from a plurality of disk drives that are installed on a computer system. Such an apparatus and method provides flexibility for booting from one of a plurality of devices.

[0025] Although the present invention has been described in terms of certain preferred embodiments, other embodiments apparent to those of ordinary skill in the art are also within the scope of this invention. Accordingly, the scope of the invention is intended to be defined only by the claims which follow.