What is Disk Compression Software?

Disk compression software is a technology that can increase the amount of information stored on a hard disk. Unlike file compression tools that require users to specify which files to compress, disk compression tools automatically perform compression and decompression without requiring users to be aware of their existence.

Such programs compress data when it needs to store information and decompress it when it reads information. Disk compression tool will overwrite

Disk compression programs create a large file, making it a virtual hard disk. This is similar to dividing a single physical drive into multiple virtual drives. The compressed drive is accessed (accessed) by a device driver. ^[2]

Disk compression compresses existing drives

All drives are initially empty. Utilities that create drives often provide a "compress current drive" feature. Its process is usually:

1. Create an empty compressed drive and store it on an existing drive.

2. Transfer existing files on the old drive to the new compressed drive.

3. Increase the size of the new compressed drive as needed to accommodate more files, and leave free space after completion.

4. After all files have been transferred, switch the drive letter. ^[2]

Disk compression compressed boot drive

Note that the corresponding device driver must be loaded when accessing the compressed drive. Compressed drive C: The boot program needs to be changed as follows:

1. BIOS loads sector 0 of the physical drive (Master Boot Record)

2. Partition sector loads sector 0 of the bootable partition (volume boot record). In this case, it is the host drive.

3. (If DOS is taken as an example) The sector 0 of the host drive is loaded, and the DOS BIOS (IO.SYS, IBMBIO.COM, etc.) is loaded.

4. The DOS BIOS loads the DOS kernel (MSDOS.SYS, IBMDOS.COM, etc.).

5. If the DOS supports the preload API, the DOS BIOS attempts to load a preloadable compression driver (look for DBLSPACE.BIN, DRVSPACE.BIN or STACKER.BIN from the root directory of the host drive) and attempts to communicate with it through the DOS preload API. If the driver responds as expected, the DOS BIOS retains the driver, otherwise discards it. If reserved and properly configured, the drive letters may be swapped, making the compressed drive C :.

6. The DOS BIOS starts CONFIG.SYS processing; it looks for files in the root directory of the boot drive. Take DR-DOS as an example, DCONFIG.SYS, etc. If present, will take precedence over CONFIG.SYS.

7. Compression drivers loaded through the preload API may be loaded through a DEVICE statement.

8. Depending on the configuration, the drive letter may be switched if it has not already happened so that the compressed drive becomes C :.

9. Continue from the compressed drive. ^[2]

Disk compression performance impact

On systems with slow hard disk performance, disk compression may increase system performance. This is for two reasons:

• After being compressed, the amount of data stored is reduced.

• One batch of disk accesses gets more content.

If the system has to wait frequently for hard disk access to complete (I / O bottleneck), converting the hard disk to a compressed state can significantly increase the system speed. But data compression and decompression will increase CPU usage. If the system has encountered a CPU bottleneck, disk compression can reduce overall performance. ^[2]

Disk compression disadvantages

There are some common disadvantages of using disk compression:

• Not all compression tools can confirm errors in the FAT file system before compressing the disk. Certain errors, such as cross-linked files, may cause additional data loss during conversion.

• A compressed drive is only visible when the device driver is loaded and the compressed drive is mounted. The boot disk may not contain the required drivers. (This is usually not a problem for solutions bundled with the operating system, unless it is starting a foreign operating system. Because programs like SYS have been modified by default to copy the compression driver to the boot disk, so the corresponding operating system can Find them on a drive other than the boot disk.)

• If the expanded data of a compressed disk exceeds the normal disk capacity, uninstalling (uncompressing) encounters problems.

• Users may not realize that large files on a host drive are compressed disks. Although it is usually "hidden" by default, users may still be curious to find a large file and can delete it. This usually results in data loss. ^[2]