Method and computer system for integrating a compression...

Electrical computers and digital processing systems: multicomput – Computer-to-computer data routing – Least weight routing

Reexamination Certificate

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Details

C713S002000

Reexamination Certificate

active

06453363

ABSTRACT:

TECHNICAL FIELD
This invention relates generally to a computer method and system for device driver management, and more particularly, to a computer method and system for integrating a compression system with an operating system.
BACKGROUND OF THE INVENTION
As a general rule of thumb, a user of a computer system will eventually run out of secondary storage space. Therefore, it is always desirable to have new methods of increasing a secondary storage volume's storage capacity. One traditional method of increasing a volume's storage capacity is manually directing the operating system to delete unnecessary data from the volume, thereby freeing space for new data. This method is undesirable because often a user will make a hasty decision about what data should be deleted and then regret that decision later. Additionally, sometimes all of the data on a volume may be important so as to preclude their deletion.
Another method of increasing the storage capacity of a file-based volume is compressing individual files and storing the compressed files on the volume. Drawbacks of this method include the requirement that users must explicitly compress a file to save space, and must explicitly decompress a file before it can be used.
Yet another method of effectively increasing the storage capacity of a file-based volume is dynamically compressing files, storing the compressed files, and then decompressing the files as they are retrieved. Compression systems utilizing this method have typically taken the form of an add-on package to an operating system. These compression systems are typically installed as a device driver with a drive letter assigned. The compression systems typically store the compressed files in a “compressed volume.” The compressed volume is a single file (a “compressed volume file”) stored on a host volume along with other files or directories. A compressed volume is treated as a logical volume with its own device driver through which the compressed volume file is accessed. Like other volumes in the computer system, each compressed volume and host volume is assigned a unique drive letter (e.g., A, B, C, and so on). Thus, if a compressed volume file is stored on a host volume that is assigned drive letter D, and the compressed volume is assigned to drive letter E, then references to drive letter E will access the files stored in the compressed volume file that is itself stored on the host volume with drive letter D.
FIG. 1
is a block diagram of a conventional computer system
100
. The computer system
100
comprises a read-only memory (ROM) device
101
, a central processing unit (CPU)
104
, a removable volume drive
105
(i.e., a floppy disk drive), a fixed volume drive
106
(i.e., a hard disk drive), and a random access memory (RAM) device
107
. A boot program and a basic input/output system (ROM-BIOS)
103
are stored on the ROM device
101
. An operating system
110
, such as MS-DOS 5.0 by Microsoft Corporation, is shown stored on the fixed volume, but can also be stored on the removable volume.
The installing of device drivers, such as compression drivers, typically occurs during system initialization. During system initialization, the operating system installs device drivers for both standard and non-standard devices that are specific to the particular hardware configuration of the computer system. For example, standard devices are typically two floppy disk drives and a hard disk drive. The device drivers for these standard devices are included with and installed automatically by the operating system. In MS-DOS, these standard device drivers are referred to as IO.SYS drivers. If a computer system includes non-standard devices, such as a CD-ROM drive, then a device driver for each non-standard device is specified in a configuration file. In MS-DOS, this file is named “CONFIG.SYS.” The CONFIG.SYS file is a user-configurable text file containing commands that are executed each time the computer system is initialized. The commands instruct the operating system how to handle certain operations and devices. For each non-standard device, a user supplies a device driver and specifies it in the CONFIG.SYS file to enable the operating system to install the appropriate device driver. Table 1 contains sample commands commonly found in the CONFIG.SYS file.
TABLE 1
DEVICE=RAMDRIVE.SYS
DEVICE=CDROM.SYS
DEVICE=SCSI.SYS
FILES=40
BREAK=ON
LASTDRIVE=E
BUFFERS=20
SHELL=C:\DOS\COMMAND.COM/P/E:256
DEVICE=C:\WINDOWS\HIMEM.SYS
STACKS=9,256
The command“device=” specifies that the following file name is the name of a device driver that is to be installed. As the CONFIG.SYS file is processed, the operating system installs a device driver by loading and initializing the device driver. As part of the installation, one or more drive letters may be assigned to the device driver.
During initialization, the device driver specifies the number of drives that are controlled by it. A single device driver can control multiple drives. The operating system uses that number of drives to assign drive letters. The operating system assigns the next drive letters currently available in the computer system. For example, if the last assigned drive letter is E and the device driver being installed supports four drives, then the operating system will assign the drive letters F, G, H, and I to the device driver. The drive letter assignments are thus dependent upon the order of the device commands in the CONFIG.SYS file.
Typical computer systems utilizing compressed volumes utilize a compression system device driver to interface with a compressed volume file. For example, the line “device=COMPRESS.SYS,” if placed in the CONFIG.SYS file, would cause the compression system device driver contained in the COMPRESS.SYS file to be installed. The operating system assigns a unique drive letter to the compressed volume.
The assignment of drive letters may be important because computer programs, when configured, typically expect certain devices to be assigned certain drive letters. If the device is assigned different drive letter, then the program does not work properly. The program can be reconfigured to expect a different drive letter, but reconfiguration can be time-consuming. Alternatively, a user may be required to reassign drive letters manually to correspond to the expected assignment.
Those skilled in the art will appreciate the problems that can arise when compression systems are installed as a device driver specified in the CONFIG.SYS file. For example, the presence of the extra compressed volume device may change drive letter assignments of other non-standard device drivers. Also, a user may inadvertently delete the command specifying the compression system device driver or change the parameters of the command resulting in the compressed volume being inaccessible.
Problems can also arise when a user instructs the computer system to compress data on a host volume (e.g., the C drive). Compression systems typically compress all of the data stored on the volume and store the compressed data in a compressed volume file. The operating system then assigns a drive letter (e.g., D drive) to the compressed volume. When the programs executing on the computer system attempt to reference a compressed file with the drive letter of the host volume, an invalid file reference will occur because the compressed file is accessible only through the compressed volume. For this reason, the drive letters for the compressed volume (D) and its host volume (C) are usually swapped so that the compressed volume is identified by drive letter C and the host volume is identified by drive letter D. Typically, compression systems swap drive letters by placing a command line in the CONFIG.SYS file immediately after the compression system is loaded. However, a user may inadvertently remove this swapping command.
Yet another problem with installing compression systems is the potential for invalid file references. If a compressed volume

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