Because these concepts are so important, we will take another brief look at them and bring our new subscribers up to date. This time, rather than giving a long abstract explanation, I'll cover the applied value of each concept briefly. For a more in-depth treatment of each, look at past Getting Started columns, consult the HP 95LX User's Guide, or pick up an introductory book on personal computing.
Files
This is the single most important concept you should understand. Your PHONE book, MEMO notes, APPT book, 1-2-3 spreadsheets, and HP CALC equations are all stored in separate files. When you save a file in any of these applications, the information contained in the file is accessible upon demand. In addition, you can transfer such files to other computers.
CAUTION: Remember that when you add something to any of these files (i.e., a new address to your Phone Book), the addition does not become a permanent part of the file until you save the file. (In MEMO, PHONE, and APPT you save a file by pressing (MENU) File Save (ENTER) Yes.)
When you save a file for the first time, you are asked to give it a "filename" between one and eight characters long (filenames may not include blank spaces). Examples of some legal file names include BUDGET, YEAR_END, and SAM-MEMO. The 95LX automatically "completes" the name by adding a three character "extension" to the filename. MEMO adds .TXT, PHONE adds .PBK, 1-2-3 adds .WK1, APPT adds .ABK, and HP CALC adds .EQN. When you go into FILER and look at file names, you can easily identify the application the file was created by from its three character extension.
Bytes
The number of bytes in a file is a measure of the size of the file. Each byte contains approximately one character (i.e. a letter, number, punctuation mark, etc.) worth of information. One kilobyte refers to 1024 bytes (and is abbreviated by the letter K). So a 12K file has roughly 12,000 characters worth of information.
RAM Disk
The HP 95LX comes with a built-in RAM Disk (designated as the C drive). When you save a file, by default you save it to the C drive -- onto the built-in RAM Disk. The double-A batteries (and if they fail, the backup battery) provide the energy needed to maintain your files in RAM. If all batteries go dead, you lose the files on your RAM drive. On a 512K 95LX you start with 254K of RAM disk. On 1MB unit you start with 398K of RAM disk. The size of the RAM disk can be increased or decreased as described in the next section.
System RAM
When you run an application such as PHONE, a copy of your phone book file is stored in temporary System RAM. When you add a new phone number, the temporary copy of the file is updated. Saving the phone book file by pressing (MENU) File Save (ENTER) Yes makes the updated temporary PHONE file the permanent file.
On a 512K unit there is a total of 512K of RAM that gets divided between System RAM and RAM Disk. If the RAM disk has 254K then System RAM contains 258K. Similarly, a 1 Meg unit contains 1024K bytes of RAM. Initially that gets divided, 398 RAM Disk, 626 System RAM.
You can change the System RAM / RAM Disk ratio by closing all applications and pressing (<Shift>)-(FILER) System Memory. Then use the left or right arrows to adjust the ratio and press (ENTER) (ENTER) to set the change.
The greater the size of the RAM Disk, the more space you have to permanently store files. The greater the System RAM, the more applications (PHONE, MEMO, etc.) you can run at the same time. A larger System RAM also means that you can open bigger files (i.e. larger 1-2-3 worksheets). Therefore, if you want to switch back and forth between large PHONE, APPT, 1-2-3, and MEMO files, you might need to increase the size of the System RAM.
Directories
When you save a file, you save it into a directory. The HP 95LX comes with the C directory built in. In addition, there are two subdirectories built into the C directory: _DAT and _SYS. If you open up FILER you'll see _DAT, but not _SYS. That's because _SYS is a "hidden" subdirectory (more on this below).
PHONE, COMM, APPT, and HP CALC files are automatically saved to the C:\_DAT directory. 1-2-3 files are saved into the C:\ directory. The simplest way to get a practical understanding of this is to go into FILER. If the top line says C:\ you can press (<DownArrow>) to see the names of all the files in C:\. To move to C:\_DAT directory, put the black cursor line on _DAT and press (ENTER). To go back to C:\, put the cursor on the line that says .. View Up and press (ENTER).
Remember the hidden _SYS directory. It doesn't display in FILER as a subdirectory of C:\, but it's still there and you can go to it and view it's contents. With the cursor in the C:\ directory press (F5) (Goto), type in _SYS and press (ENTER). You should get a listing of the files in the _SYS directory. These files are in permanent ROM. They can be copied elsewhere, but cannot be erased or modified and resaved to the _SYS subdirectory.
Spending the time needed to understand these concepts will make your HP 95LX computing simpler and more effective.