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COMPUTER BITS BY DARREN YATES Using DOS 6.0’s DoubleSpace If you’re having problems with hard disc space, then you should take a long look at DoubleSpace in DOS 6.0. It will com­press existing drives as well as create compressed drives inside your current setup. No matter how big your hard disc is, you never seem to have enough space on it. One reason: computer programs are getting bigger. Take a look at the evolution of MS-DOS, for example. Version 3.3 occupied 500Kb or so, while version 6.0 takes 6-7Mb. But that’s not large compared to some programs. The current version of Corel­Draw requires upwards of 30Mb of disc space! To alleviate space problems, many computer users rely on file compression programs such as LHARC and PKZIP. These are great little programs which can compress most files down drive – you simply save your files to that disc and they are automatically compressed. It can even compress some of your files so that they are 16 times smaller than the original size. The obvious benefit is that it dramatically increases disc space. And although it will marginally slow things down, as files compress and decompress, it is still many times faster and re­ quires less work than LHARC or PKZIP. Running DoubleSpace To get DoubleSpace up and running, simply type DBLSPACE<return> at DoubleSpace can create a compressed drive which, for all the world, looks & acts just like an ordinary drive – you simply save your files to that disc & they are automatically compressed. to a fraction of their former selves. However, they do require some effort on your part in order to compress files and delete the originals. To recover the original files, you then have to run the compression program in reverse to decompress the files back to their original size. DOS 6.0’s DoubleSpace goes a step further by making this process automatic. DoubleSpace can create a compressed drive which, for all the world, looks and acts just like an ordinary 34  Silicon Chip your C:\DOS prompt. Once the program appears, you will be given the choice of running two methods of setup – express or custom. Express setup automatically selects all files on drive C: to be compressed and sets the compression ratio as well. The custom option allows you to set the size of the drive and specify a free space ratio from 2:1 to 16:1. In addition to hard disc compression, DoubleSpace also has the ability to compress other drives that MS-DOS can access, except CD-ROMs and the like. This means that you might want to compress a 1.44Mb floppy, for example, to transfer files from one machine to another without having to compress part of the C: drive as well. Fortunately, there is a way around Microsoft’s statement that “once a drive has been compressed it can’t be decompressed”. The method is as follows: (1) Use the Custom Setup and select the option for creating a new compressed drive. This new drive will come from the remaining space left on your existing C: drive. (2) Follow the options through but don’t change any of the de­faults to create the new compressed drive. This will be designat­ed as drive H:. (3) Once that’s completed, exit out of DoubleSpace. DoubleSpace is now installed on the hard drive and can be accessed as a normal program. To retrieve your original disc space and remove the compressed drive H:, the steps are as fol­lows: (4) Return to the root directory of your C: drive – you will find that you have around 2.5Mb of memory left. This is determined by the custom setup procedure in DoubleSpace. ( 5 ) Ty p e AT T R I B - S - H - R DBLSPACE.*[enter], then DIR[enter]. You will find two new files with the DBLSPACE prefix. One of these, DBLSPACE.001, will be approximately the same size as the space originally remaining on your hard disc minus the 2.5Mb now remaining. (6) The ATTRIB statement allows this file to be seen and, more importantly, to be deleted. If you now type DEL DBLSPACE.001[enter], you’ll find that you’re just about back to the same space you started with. Now go back into DoubleSpace and check that the drive is no longer there. This should be apparent on the opening screen. It will either show that there is no compressed drive or that it still thinks drive H: exists. If the latter is the case, just select the UNMOUNT option from the DRIVE menu. This will remove it from DoubleSpace’s setup files and you can now compress other drives without having your hard disc disturbed. User environment Once you start using DoubleSpace, you’ll find it an easy program to work with. As with all Microsoft software these days, it comes with a context-sensitive help reference that is quite thorough and contains information that doesn’t appear in the DOS 6 handbook. If at any point you get stuck, simply press F1 and Double­Space will give you information on your current position. There are four main options displayed across the top menu bar: DRIVE, COMPRESS, TOOLS and HELP. This second help option allows you to look up anything you want at any particular time, instead of being context sensitive. The DRIVE menu contains the main disc-based commands which include MOUNT and UNMOUNT. These are the commands for loading and unloading a compressed disc into your current system. You can’t just load a compressed floppy into your B: drive and expect it to work immediately; you have to use the MOUNT and UNMOUNT commands to tell DOS that the current floppy is either a compressed or normal disc. Other commands included are CHANGE RATIO and CHANGE SIZE. The change ratio command allows you to modify the estimated disc space displayed. When a drive is initially compressed, the amount of free space is only an estimate. Because not all files compress equally, it is difficult to forecast how much compressed space remains on a drive. Once you begin using the drive, the free space shown will be based on the average compression ratio of all files stored so far. You can check the average compression ratio for all files in a directory by typing DIR/C[enter]. This will also give the compression ratios on each file as well. Note that the CHANGE RATIO command changes the estimated disc space remaining but not the compression ratio of any stored data. When DOS shows how much space remains on a compressed disc, it is an estimate based on a theoretical compression ratio of 2:1. You can increase this up to 16:1, which is the limit of the compression range. In practice, it really depends on the files the disc will contain. If you’re only copying text files, which compress up much tighter than 2 to 1, changing the ratio make sense but if the disc contains .LZH, .EXE or .BIN files, which don’t compress anywhere near 16:1, then it would be pointless as the free space shown will be inaccurate. The CHANGE SIZE command allows you to change just how much of a drive is compressed and how much is normal storage space. This can be very handy indeed. Since Double­ Programming Tip This tiny batch file, A_.BAT, will automatically mount your compressed floppy disc and get you into the A: drive. For other drives, simply change the drive letter. Just type A_[enter] and it does the rest. The <at> symbol stops unnecessary messages appearing on the screen: <at>dblspace/mount a: <at>a: part of a drive that you already have in use. The Create New Drive option allows you to create a new drive from an existing hard disc which has its own designation letter; eg; you can create a new drive G: from space left over on your C: drive. This is handy if you wish to separate users or programs, or both. Tools menu In a way, DoubleSpace is a disc operating system within another and this is shown up in the way that DoubleSpace looks after its own compressed drive. An example of this is the Tools Menu. This contains two options: defragmentation and error remov­al. The defragmentation option rewrites all file fragments into consecutive sections of disc. This speeds up file loading as well as reducing disc wear and tear, since the drive only has to look at one place on the drive to find the complete file. Error removal is achieved using a modified version of the CHKDSK program. This unmounts the disc so that it appears as an ordinary disc and runs a CHKDSK test looking for errors such as bad sectors or lost files. Once found, they are then removed. There aren’t many commands in DoubleSpace and this makes running a compressed disc drive system easier than you might have thought. If you find this a bit cumbersome, then you’ll be pleased to know that DoubleSpace is also operable from the DOS command line. DOS commands Space always gives compressed drives a new letter designation, you could quite easily put program .EXE files on the normal section of the disc and then place work files such as text and database files on the compressed section. This will give you an optimum arrangement between maximum storage and speed. Compress menu Moving across to the Compress menu, this gives you the option of compressing an existing drive or creating a new com­pressed drive. Now you might think this sounds like the same thing but there is a difference. The Compress Existing Drive command allows you to compress all or By typing DBLSPACE /?[enter], Double­Space will give you the list of switches which can be used to achieve all of the above options directly from the DOS prompt rather than having to access the main user interface. This is ideal for batch file programming or for using DoubleSpace in your own programs. And by chaining in the DOS commands, you can access the features on DoubleSpace quickly and easily (see the programming tip in this column). So that’s it. You may have dismissed DoubleSpace as just a sales gimmick the boffins in the computer stores use but it is a definite winner and well worth using if a hard disc upgrade is beyond your budget. For the money, SC it’s a bargain. October 1993  35