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RAM Charger 8 For Macintosh
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What is RAM Doubler (RD), and should I use it?


(Tech0015A -- 05/17/99)
RAM Doubler is a replacement for Apple Virtual Memory.

From the viewpoint of "memory", Connectix RAM Doubler VM provides the same features as Apple VM, and thus the advice on our page "Should I use VM?" applies to RAM Doubler as well.

This explains why you find comments like this slip into the few RAM Doubler docs that exist:


                  Next, try turning on Apple's Virtual Memory in the Memory Control and
                  restart the Macintosh. If the same problem occurs with Apple's Virtual
                  Memory, it is also very likely to have the problem with RAM Doubler since
                  each employs a form of extended memory. It would then be necessary in
                  this case to determine which software is not working properly with extended
                  memory in use.

And comments like this:


                  If RAM Doubler is installed, there are a few programs (usually old ones)
                  that might see "extended memory" and assume that Apple's Virtual Memory
                  is in use, even if it is actually RAM Doubler that is providing the extended
                  memory. If a program is not designed to work with extended memory in use
                  and RAM Doubler is installed, it may display a message that says "Virtual
                  Memory is on" and that it should be turned off. If this occurs, there is a
                  simple alternative. Restart the Macintosh and disable RAM Doubler
                  temporarily by holding down the tilde (~) key or the escape (esc) key during
                  startup. This will disable RAM Doubler for that session. RAM Doubler will
                  reload on the next restart. 

Connectix would lead you to believe that these comments are coincidental, when in fact RAM Doubler's "extended memory" is simply virtual memory - and thus the common problems are not coincidental. Like all virtual memory, RAM Doubler employs the processor's Memory Management Unit to provide a virtual memory address space, handling interrupts to service memory needs using real memory and backing store. Call it "roses", but it is still VM (which is a valuable item in its own right), and it is not RAM Charger.

(Humor: perhaps you will find it as ironically amusing as we do that our artificial arch competitor now seems to be the only virtual memory solution that allows users to use VM and RAM Charger under OS 8.5.1 and 8.6! Ha! Ha! - read more here)

However, there are a few issues that might make you choose either Apple or Connectix over the other. If yo are so inclined, a somewhat less technical approach to this topic is taken on the web page "How does RAM Charger compare to RAM Doubler (virtual memory)?". But, since Connectix is never up front about the technical issues, here is the real stuff so you can make an informed choice.

Despite all other claims about "how" RAM Doubler does what it does (claims that are unimportant to the end user, and claims that are often contorted and/or misrepresented to make it sound impressive), and Connectix's attempts to coin the term "extended memory", RAM Doubler VM has only four significant differences from Apple VM:

In Favor of RAM Doubler

1) RAM Doubler VM doesn't reserve disk space, and is less likely to spin your disk.

2) RAM Doubler VM claims to be faster than Apple VM.

** It may be the only way to run VM and RAM Charger under OS 8.5/6 (read here)

Against RAM Doubler
3) RAM Doubler (2) VM provides five VM sizes, Apple VM sizes are unlimited.

4) RAM Doubler costs money, Apple VM comes free with your system.

1) If you do not care about hard disk space, #1 is unimportant - unless you are running a notebook and may care about battery life. Apple reserves a portion of your hard disk eqaul to the amount of virtual memory set in the "memory" control panel. And, because of the techniques it uses, apple is more likely to spin your disk more often. RAM Doubler can go much farther before needing to use any disk space, and it does not reserve the disk space in advance.

2) We have never seen any benchmarks on #2. Personally, I run Apple VM on my 7.6.1 machine and do not notice a significant slowdown, but then I do not push it very hard very often. This is very subjective, and I do not have a rock solid opinion. In the early days of RAM Doubler is was painfully obvious the RD outperformed old Apple VM, but we do not see the obvious glaring discrepancy these days. In support of RD claims, theoretically a slow disk may slow down Apple more than RD - but again this is how, not what, and all that is important is the question "is it faster on your machine", not "why is it faster"? Since no RD demo is provided, nor are any benchmarks made available, we have no idea how you can evaluate the performance.

3) Apple lets you set any value starting at 1 meg over real RAM (the "1 meg over" limitation is arbitrary as far as we can tell), whereas RAM Doubler 2 limits you to five fixed levels for absolutely no good reason. RAM Doubler does allow you to set your memory to "File Mapping" which a misleading label for "your real RAM amount", 1 meg less than Apple VM allows.

4) Cost. Free vs. Fee, you choose.

We run RAM Doubler on a Powerbook since it has a lot of RAM and limited disk space, and since we care about battery life. We also run it on a few other machines which are low on disk space, and on which we do testing, but we don't know that we can tell the difference in performance between RAM Doubler and Apple VM on these other machines.

But doesn't RAM Doubler add the new File Mapping functionality?

File Mapping is in no way a product of Connectix RD, nor a concept introduced by RD, nor a feature exclusively available in RD. File mapping is an _aspect_ of virtual memory, provided on the Mac by both Apple and RAM Doubler (also provided in Unix and probably most Window OS implementations). File mapping provides "read-only" virtual memory, efficient since it never has to be "swapped out" since it has backing store already on the disk (the mapped file).

By our best guess, File Mapping was introduced in Mac OS approximately OS 7.1.2, and may have always been supported by RAM Doubler - since it arrived later. But hey, VM is not our domain so we are not absolutely sure on the tame frame.

Running approximately OS 7.1.2 on a PowerMac, File Mapping is ONLY active and is ALWAYS active when VM is enabled (Apple VM or RD VM) - regardless of the "multiplier/amount" setting selected. (As far as we know File Mapping is only available when running PowerPC - though it seems logical that a 68K code fragment could exist in the data fork of a file and be "File Mapped", we have seen no proof that a 68K implementation of File Mapping was developed).

Connectix has taken great liberty with its labels and descriptions in an effort to confuse the VM issue, and has obviously succeeded in this case - leading some users to believe that File Mapping is a "Connectix" product by using the "File Mapping Only" label in their control panel.

The "multiplier-slider" setting in RAM Doubler 2 is the direct equivalent of the amount of memory you can set in the Memory Control panel under Virtual Memory when virtual memory is "on" - though Apple provides more versatile control, rather than a limited set of predefined "multipliers".

With "File Mapping Only" selected in RAM Doubler, RD doesn't multiply the "total memory" amount, it just turns on [it's one and only form of] VM. Thus, "File Mapping Only" is the logical equivalent of enabling Apple VM with lowest possible multiplier/amount (1 meg over real RAM). The label "File Mapping Only" does not mean VM is disabled, despite the literal interpretation. VM is fully active. "File Mapping Only" is a misleading label whose real meaning is better conveyed by the labels "Single", "None", or "no multiplier", and running under the settings is functionally equivalent to running with Apple VM enabled to the lowest possible amount.

Isn't RAM Doubler the same thing as RAM Charger?

No. RAM Doubler is virtual memory. Virtual Memory increases your memory, but does not change the way it is distributed to applications. RAM Charger, on the other hand, changes the way your memory is distributed to to applicitions, but does not increase it. Details on the differences between RAM Charger and vitutal memory are discussed on the page " What REALLY different between RC & VM?", and the basics about VM are covered on the page " Apple VM & RAM Doubler VM (virtual memory)...".

Both RAM Charger and virtual memory (including RAM Doubler virtual memory) may be used together on the same machine, and usually compliment each other.

Why is RAM Charger more complex the RAM Doubler?

This is a direct reflection of the unprecedented enhanced functionality added by RAM Charger, and its inherent complexity. Since RAM Doubler does the same thing as Apple Virtual Memory, which is intended to be a transparent "memory substitute" for users, very little user interaction is required. For marketing purposes, which proved successful, RAM Doubler added the least possible new functionality beyond Apple VM (new features described above). However, RAM Charger adds extensive control and feedback that was previously unavailable for other aspects of application memory usage.

Compatibility with applications was also relatively assured for RAM Doubler, while it was not for RAM Charger. Since virtual memory already existed before RAM Doubler, most all applications were tested with VM and related bugs were worked out - thus RD had very little trouble. The popularity of RD encouraged any rogue applications to come in line with VM. Again, note the Connectix comment here:


                  If RAM Doubler is installed, there are a few programs (usually old ones)
                  that might see "extended memory" and assume that Apple's Virtual Memory
                  is in use, even if it is actually RAM Doubler that is providing the extended

If RAM Charger had been better understood, accepted and used in the industry (or adopted by apple and integrated into the system by Apple) then application developers would have been encouraged to test with it and work out relevant bugs (which would just mean adhering to programming standards documented by Apple). Moreover, we would have had greater revenue to simplify our interface and would have had enough clout to encourage developers to work with us (rather than the we don't care attitude of some developers). As it was, RAM Doubler got a free ride on Apple VM's history, and RAM Charger is on its own as a whole new thing.

It is also interesting to note the with Mac OS X, which now implements the logical next step "RAM Charger style" dynamic memory model (already commin on other OSes like Uinx and Windows), applications will have to be re-written to take advantage of this new model - RAM Charger might have helped prepare some application developers for this step.


We use RAM Doubler on some of our machines, and are pleased with the results in many cases. However, Apple VM provides the same functionality and it is only reasonable that people understand this. The only functional differences between Apple VM and RD VM are reserved disk space usage, alleged speed difference, and the size of memory you may specify.


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