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BUILT-IN RAM: PART 2 -- SYSTEM RAM
What is System RAM, the RAM Disk, and the relationship between them? How do you adjust the ratio between them and what do you have to watch out for?
By Hal GoldsteinIn the last issue we discussed "long term" memory -- the RAM Disk. We emphasized the importance of saving our memo, address, appointment, equation, and Lotus files to the RAM Disk. In the discussion we also introduced the concepts of RAM Card, File, A Drive, C Drive, Byte, Kilobyte, and most importantly the meaning of "replacing current file."
In this column we will talk about "short term" memory, also known as System RAM.
WHAT IS SYSTEM RAM?
Suppose we are in a meeting and we want to make some notes in the 95LX's MEMO program. We press <MEMO> and type several phrases.
The HP 95LX "remembers" those phrases: the phrases remain, even if we do not take more notes for a while, and the HP 95LX turns itself off in five minutes.
Those phrases remain in short term memory, in System RAM.
The HP 95LX is actually always "on" as long as its batteries remain good. When we turn the HP 95LX "off" by pressing ON again, we are really just turning off the screen and other internal mechanisms that consume battery strength. The computer itself remains on.
Therefore, when the HP 95LX screen goes blank from five minutes of non-use or from pressing ON, all our work in short term memory (System RAM) remains alive. This is very convenient since we may have just added a new phone number and notes from the meeting. We then get absorbed in the meeting. A half hour later, we press ON to turn the screen back on, and the phone number is not lost, and we can resume our notes.
The most important point to remember is that until we Save our work to the C Drive RAM Disk or an A Drive RAM card, the work is not permanent. The phone number can get lost, the notes from the meeting can disappear.
Suppose we are taking notes at our meeting in MEMO. In the course of the meeting, we add several appointments in APPT to our appointment book. We also add a phone number in PHONE. We also open Lotus to look up some numbers on a spreadsheet. Finally, we modify one of our HP Solve equations as a consequence of some of the discussion in the meeting.
Given the scenario described above we have "opened" a MEMO file, an APPT file, a PHONE file, a 1-2-3 file, and an HP CALC file. Even if the HP 95LX shuts itself off after five minutes, these files remain open in System RAM.
To prevent the possibility of losing our work, we will want to "save" any modified file to our RAM Disk (C drive) or RAM Card (A drive).
Since the meeting notes is a new file, within MEMO we would issue the Menu File Save meeting command to save the file with the name MEETING.TXT (MEMO automatically adds .TXT unless we tell it otherwise).
The Lotus file we opened was only for reference. We made no changes to the Lotus spreadsheet. Therefore, there is no need to save the file again.
The APPT, PHONE, and HP CALC files are another matter. These files previously existed (were previously saved). We have now modified these files (i.e. by adding a new phone number to the open PHONE file, appointments to our APPT file, and a modification to the equation in our HP CALC file). Our new modifications to these files have only been made in short term System RAM. On our RAM disk resides APPT, PHONE, and HP CALC files as they were before we modified them.
When it is time to save our APPT, PHONE, and HP CALC files, we will use the Menu File Save command in the given application. In PHONE and APPT we are asked whether we wish to Replace current file? In HP CALC we are asked whether to Overwrite equation file? In either case the question is the same. Do we want to replace the file that is currently on the disk with a copy of our newly modified file. In most cases the answer will be yes.
Let's look at some of the ways that it is possible to lose work in System RAM if it has not been saved to the RAM Disk.
Let's say that when we enter SET UP (press <Shift>-<FILER>), it shows RAM Disk at 254K and System RAM at 258K.
What does that mean? Can we change those numbers? Why would we want to change those numbers?
The RAM Disk / System RAM numbers mean that we have 254K reserved for our C drive RAM disk and 258K left for System RAM. This ratio can be changed by entering SET UP, pressing System Memory, and using <Left Arrow> or <Right Arrow> to adjust the ratio (listed at the bottom of the screen). Press <ENTER> to lock in the change before pressing Quit.
However, before the HP 95LX will let us change that ratio, it insists that we first close any of our open files. In other words we will need to go into each application in which we are working on a file and exit that application. Remember, save any files in which we made changes. If we exit a program without saving our work, we will lose any modifications to that file since the last time we saved it.
After closing all our applications, return to SET UP and change the RAM Disk /System RAM ratio. The HP 95LX will not let us make the RAM Disk size smaller than the size needed to hold the files we currently have stored on the C drive.
WHY WE MIGHT CHANGE THE RAM DISK / SYSTEM RAM RATIO
As we become more sophisticated in our use of the HP 95LX, there are a number of reasons why we might want to change the RAM Disk / System RAM ratio. In doing so we must weigh the pros and cons. For example, we might want to optimize the size of our RAM Disk to be able to save more files. However, by doing so, we may only be allowing ourselves the ability to keep one or two of the built-in applications open at any one time. (The built-in applications use the System RAM we just gave up to make a larger the RAM Disk.)
Why we might want to increase the RAM Disk, thus decreasing System RAM:
THE FUTURE OF THIS COLUMN
I need to find out if you found "Getting Started" helpful, and whether we should continue it. Please drop me a note if you wish me to continue discussing the basics. If the column is too elementary or not elementary enough, tell me. Also, if there are topics you wish me to discuss, please mention that.
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