The REPLICATE command /R that reproduces similar formulas in adjacent rows and columns.
The GLOBAL command /G that changes the columns width (fGC) and the way numbers are formatted (fGF).
The TITLES command /T that fixes rows or columns of alpha-betic titles in place, as part of the top or left hand "border."
The WINDOW command /W that splits the screen, either horizontally or vertically, into two independently scrollable, formattable windows.
Much of the power of VisiCalc is due to the simple and highly consistent way in which these commands interact with one another. In almost any context, a command will do what you would logically expect.
3. Aside from the replicate command, which baSically saves you time as you write formulas, all of the commands discussed in this lesson affect only the appearance of your work on the screen understand something, go back through this lesson to see what you might have missed. Also check Part III, the VisiCalc Command Reference section and the VisiCalc Reference Card for more complete explanations. Once you under-stand the fundamentals of this lesson, you'll know enough about VisiCalc to begin using it effectively.
Postscript: Memory and the Electronic Sheet
As you may know, your computer contains two kinds of fast semiconductor memory: RAM and ROM. ROM or "Read Only Memory" is manufactured with a fixed pattern of data or program instructions stored in it. RAM or "Random Access Memory" is made in such a way that it retains data that is put into it only as long as the memory's electric power is left on or until new data is put into the memory in place of the old data. Data or program instructions are put into RAM memory either by typing at the keyboard or by loading prerecorded programs or data from cassette or diskette.
The VisiCalc program is loaded into RAM memory from diskette, and it, to-gether with some RAM that the computer itself requires, takes up about 26K bytes. The remainder of RAM memory is devoted to the VisiCalc electronic sheet. VisiCalc manages this area of memory automatically. You never have to concern yourself with the details of how the electronic sheet is maintained. But you will find it useful to have a general idea of how the sheet works as you begin using VisiCalc to its fullest capacity.
Essentially, VisiCalc reconfigures the electronic sheet dynamically. That is, VisiCalc expands the size and shape of the sheet as you use it. You actually start with a 1 by 1 sheet, starting and ending at position A1. Although you can
VisiCalc Shrinking the Sheet move the cursor to any position up to BK254, no memory is actually allocated for the sheet until you write something on it.
Then the sheet grows into a rectangle just large enough to include the right-most and bottomright-most positions in which something is written. If you type a long message or formula at a particular entry position, VisiCalc will reserve addi-tional bytes of memory for the position, but all of the other positions on the sheet will remain just large enough to hold the information which you have written in them. This is called "dynamic memory allocation."
VisiCalc continually displays the amount of memory available to you through the memory indicator. The memory indicator is the two-digit number located in the right corner of the prompt line just below the letter C. This number is the amount of memory in kilobytes still available for additional entries on the sheet.
With 32K of memory, this number should be 06 (or close to it). The memory indicator will vary as you write information on the sheet or use commands such as replicate, to write information.
As you move further downwards and to the right, writing labels, numbers and formulas, more and more memory is used until the available memory is ex-hausted. If you finally exhaust all of the available memory, VisiCalc will flash the exclamation point in the upper right corner of the screen, replace the memory indicator with the letter M, and refuse to write anything more on the sheet.
To sum up, VisiCalc manages memory efficienctly and automatically. Because memory is dynamically allocated and the sheet is reconfigured to suit your needs, you can work ahead of yourself in terms of memory. Note, however, that if you have a relatively small amount of memory, you certainly shouldn't be wasteful with it. Aside from noticing from time to time how much space is still available for you to write in more entry positions, you need not concern your-self with problems of memory management.
Shrinking the Sheet
One thing VisiCalc does not do automatically, however, is to "shrink" the sheet.
Suppose that you have written on various portions of the sheet, causing it to grow to a size of 100 by 100 positions. Later, having finished with this informa-tion, you might have erased or blanked out the entry positions near the right and bottom edges of the 100 by 100 sheet.
However, the sheet will remain configured as 100 by 100, although each empty position will require only 2 bytes. If you begin using additional memory by writing lengthy labels and formulas in other positions, you may want to shrink the sheet to the smallest possible configuration for the information still written on it.
To do this, you must save the sheet on diskette with the ISS command (as discussed in Lesson One), clear the sheet with ICY and reload the saved sheet with the ISL command (as discussed in Lesson Two). As the disk file is loaded, VisiCalc will enter on the sheet only those labels, numbers and formulas actually saved, and in the process the sheet will grow from a 1 by 1 configura-tion to just the size you need for the informaconfigura-tion remaining. This will make more memory space available for additional labels and formulas.
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