Switch Between Applications with Software Carousel or MS DOSSHELL

Switch between the built-in applications and as many DOS programs as you like, and never get the "out of memory" message!

By Dara Khoyi

Imagine working on a large 1-2-3 spreadsheet, then switching to your favorite but memory-consuming DOS word processor, WordPerfect 5.1. Then you look up a fax number in PHONE so you can switch and immediately run your DOS fax software program. Then it's time to relax and you start Hearts and Bones or Backgammon. Its possible to do all this on the Palmtop, but its time consuming. The memory constraints of the Palmtop force you to close down some applications to run others. Wouldn't it be great to task switch almost as fast as you could press buttons, without worrying about memory? This is what I do everyday.

This article describes a powerful and fundamentally new way to use DOS and the built-in applications on the HP 100/200LX Palmtop PC. You can test my approach out using the MS DOSSHELL application (that comes with MS-DOS 5.0 and 6.0) at no cost. If you like what it does for you, a commercial package called Software Carousel provides a more powerful approach to task switching on the HP Palmtop.

Task switching on the HP Palmtop

Task switching simply means switching from one application to another without closing down the first. HP Palmtop users task switch all the time, between PhoneBook, Appointment Book, and the other built-in applications. Switching between built-in applications on the Palmtop is fast because they are stored on an electronic RAM disk instead of a relatively slow physical hard drive.

You can open up as many built-in applications as you like until you run out of system RAM memory! Once that happens, System Manager prompts you to shut down one or more applications so you can open another program. You can also have a "DOS box" open with one DOS application active. The DOS box also shares available RAM with the System Manager applications. Because of this, it is very difficult to have a large DOS application open along with System Manager applications.

DOSSHELL and Software Carousel

These programs overcome the system RAM limitation described above. Although they have different capabilities, they function essentially in the same way. An example will help describe how these programs work.

Let's say you open a DOS word processing program to write some letters. You realize you need to check the meaning of a word in a DOS dictionary program before you use it in the letter. If you are running these DOS programs from DOSSHELL or Software Carousel, you'd simply press a pre-defined hotkey to switch to the dictionary program. DOSSHELL or Software Carousel would suspend the word processing application, saving it to a temporary file (on the A or C drive) to free-up system RAM. Then DOSSHELL or Software Carousel would start the dictionary program. After you're finished with the dictionary program, you press the hotkey for the word processor and DOSSHELL or Software Carousel switches back to the word processor in exactly the same place you left it.

DOSSHELL or Software Carousel: Which task switcher is for you?

I started out writing an article on DOSSHELL alone, but discovered that Software Carousel had been modified to work on the HP Palmtop (more on that story later). The two programs do essentially the same thing, but Software Carousel is better suited to the Palmtop because it provides greater flexibility and speed to switch between built-in applications and DOS applications than DOSSHELL.

The only major advantage DOSSHELL has over Software Carousel is that the latter is a commercial program that costs $69.95. Users with DOS 5.0 or 6.0 installed on their desktops already have DOSSHELL to experiment with. For those users, we have included a sidebar (page 37) that describes how to set up DOSSHELL on your HP Palmtop. An additional sidebar (page 38) gives some tips on using DOSSHELL and Software Carousel on the Palmtop.

The rest of the article focuses on Software Carousel and a comparison between the two products.

2001: A Carousel Odyssey

I have used Software Carousel for some years on my desktop thanks to a stroke of luck. In 1987, I attended an IBM 1000-person users meeting that was featuring a presentation by Ed Tolson, president of Softlogic Solutions, Inc., which at the time published Software Carousel. At the end of the meeting Ed picked my name out of a hat for a free copy of the program.

Over eight years later I was working on this DOSSHELL article when I was given another copy of Software Carousel to evaluate, newly modified for the HP Palmtop. Ed tells me that Stanley Kubrick (producer/director of 2001: A Space Odyssey) called them (now Sunshine Software Company) and asked for HP Palmtop compatibility. The programmer working on it got inspired and rather than just trying to make it work decided to make the Blue Keys work, speed it up, allow multiple System-Manager sessions, enable the alarm function, and so on.

How Software Carousel works

Software Carousel is a task-switching program for DOS-based computers. It was first introduced in February of 1986. It permits a user to load programs in a dozen work areas and rapidly switch among them with the touch of a key. Each work area has access to the full resources of the computer, including all of the lower 640K of RAM that it needs.

When you press a hotkey to access another program, Carousel saves a snapshot of the current program, right down to the cursor position. It then brings a different work area (and thus a different program) onto the screen. This process is much faster than saving files, closing the program, starting a new program, and loading new files. Users can work smarter, switching instantly among their programs much as they switch among other workday tasks.

Since its introduction, till the introduction of Windows, Software Carousel was the most widely installed program of its type, with several million users worldwide. Prior to the introduction of Windows 3.1, Software Carousel was the task switching environment of choice in a number of major corporations. Software Carousel's success was based on three principles of task-switching:

  1. 1. Minimal lower RAM usage -- Software Carousel, written entirely in assembly language, requires a very small amount of lower system RAM memory, which leaves more room for the programs you run.
  2. 2. Compatibility -- Software Carousels close alliance to its DOS host for context switching allowed it to work properly with every DOS program on the market, even TSRs.
  3. 3. Overall reliability and stability -- Software Carousel has been characterized as bulletproof in numerous reviews. Users reported that it never crashed, leaving you hung up with precious files unfinished and unsaved.



Born Again on the Palmtop

Today, several years after the task switching concept has been replaced in the desktop world by Windows, Software Carousel has been modified to use with the HP Palmtop.

Software Carousel has been adapted to be tightly integrated with the Palmtop's built-in applications. Carousel can detect when the built-in alarm reminder rings, allowing it to automatically switch you to the work area where the Appointment Book is running, and bring it up on the screen.

No more out-of-memory messages

Many of us have pressed too many blue keys and gotten an out of memory message. The number of System Manager applications you can run on the Palmtop at the same time is limited by available system RAM memory. However, Software Carousel (and DOSSHELL) help you overcome this limit.

Software Carousel lets you open a much larger number of applications at the same time by letting you open multiple copies of System Manager (which is, in itself, a DOS program). DOSSHELL only allows one System Manager session to be open at a time.

For example, let's say you have Carousel set up on your system and you open two applications and a large spreadsheet in 1-2-3. When you try to open a fourth application you run out of memory. You simply open another copy of System Manager from Carousel and start opening more built-in applications. You can switch between the different System Managers by pressing an applications blue key. Software Carousel knows which session is running which applications.

Storage space needed

As mentioned earlier, the way Software Carousel accomplishes these feats is by saving snapshots of open programs to disk before opening another program. To do this, Software Carousel needs file storage space on either the C drive or a Flash card disk in the A drive. Because of the limited storage space on the C drive, a Flash card is the most practical place for this storage.

When you set up Software Carousel on your Palmtop, you have to specify where the storage file is going to be and how big it will be (more on this later). Software Carousel's start-up program defragments the disk before setting up the storage file. Setting up a pre-defined storage area allows Software Carousel to bypass DOS when transferring information and use absolute Read/ Write techniques for fastest possible performance when swapping programs. The result is that switching between work areas takes less than two seconds.

Customizing Software Carousel

Software Carousel users can customize the number of work areas available, giving each a name which appears in menus. Users can also specify the amount of memory assigned to each work area, reducing the amount of RAM allocated for smaller programs. In addition, you can designate a series of commands to run in each work area each time you initially open it. This can, for example, allow you to start your favorite TSR prior to loading your application in that work area automatically.

These features, and many more, are controlled by an easy-to-use option setting program supplied with Carousel. Settings for work area names and memory allocations can be changed while Carousel is running, allowing you to adapt to changing needs on-the-fly.

Software Carousel's option setting program includes an image of the Palmtop keyboard, allowing you to easily select hot-keys and other activators. Menus have been redesigned and streamlined for use on the Palmtop and unnecessary options have been removed from the original Software Carousel to make it use less system RAM memory.

Point-by-point comparison of Software Carousel and DOSSHELL

  1. 1. Software Carousel task swaps quickly, in about 2 seconds. DOSSHELL's swap time is 10 to 15 seconds (both using uncompressed memory card).
  2. 2. The Appointment Book alarm functions works with Software Carousel no matter where you are, even in a DOS session. DOSSHELL needs the shareware application ALARM.EXE to fix this.
  3. 3. Software Carousel lets you have multiple System Manager sessions open. DOSSHELL only allows one System Manager session to be open at any given time.
  4. 4. If you are in a DOS session or a System Manager session that has not loaded a particular built-in application (Appointment Book, for example), and you press (APPT), Software Carousel automatically goes to the appropriate System Manager session and opens Appointment Book. In other words, the Blue Application Keys work, wherever you are in Carousel. DOSSHELL cannot do this. You must first go to the System Manager session and then press the Blue Key.
  5. 5. Software Carousel uses 7K less of system RAM than DOSSHELL.
  6. 6. Software Carousel requires you to determine ahead of time how much swap space you want on PC Card. I have configured my SC Swap file at 4.75MB (I have an undoubled 40 meg card) although you can certainly configure much less space. DOSSHELL, on the other hand, will take what it needs. (Note: The reason that Software Carousel asks for pre-allocation of space is so that it can set aside contiguous space and do basic low level read/writes in order to speed up swapping.)
  7. 7. Software Carousel costs $69.95. ($89.95 after 12/31/95) DOSSHELL is free for those who already have DOS 5.0 or 6.0. If you are interesting in experimenting and you already have DOSSHELL, its an inexpensive way to start. Once you decide that full task switching is a must on your Palmtop, switch to the more full-featured Software Carousel.



How to set up DOSSHELL

Tips on using DOSSHELL