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RAM Charger 8 For Macintosh
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What's really different between RC & VM (+RAM Doubler)?


(Tech0006A -- 03/03/98)

"Not Just More Memory--Better Memory"

Definition of the RAM Charger Product Category

A technical discussion of RAM Charger's unique role in the Macintosh memory market, intended for reviewers, analysts, marketing professionals, users of RAM Charger, and other interested evaluators. A somewhat less technical approach to this topic is taken on the web page "How does RAM Charger compare to RAM Doubler (virtual memory)?"


There has been much interest in--and some confusion about--the new category of Macintosh software ushered in with the introduction of RAM Charger, The Software Memory Upgrade. More details about RAM Charger's features and benefits are provided elsewhere. This note goes into some depth to address questions raised about the differences and similarities between RAM Charger and the alternatives for getting more useful memory on the Macintosh (such as System 7's virtual memory and RAM Doubler(TM) virtual memory by Connectix).

  • RAM Charger is very different from other methods of getting more usable memory for your Macintosh. Where RAM Charger optimizes allocation of the logical memory space but does not expand it, the alternatives do the opposite: they expand the logical memory space but do not optimize the use of it.
  • Optimizing memory, rather than simply expanding it, provides a unique and important benefit. With RAM Charger, applications work as if their previously fixed memory partitions can grow and shrink dynamically. So they only use the amount of memory which is actually needed at any given moment. This is especially beneficial to users who run several programs at a time or have a widely varying mix of documents and applications.
  • RAM Charger works well in conjunction with all methods of expanding the logical memory space (including RAM Doubler and virtual memory). Users who are already using RAM Doubler or VM are amazed by the increased memory, and optimization benefits they get when they use RAM Charger in addition.
  • For Macs without an MMU, and already at their physical memory barrier, RAM Charger is the only alternative for more useful memory. Since RAM Charger is designed to work with all Macintosh hardware and does not require any special processor support (such as the virtual memory mapping MMU available on 68030 and 040 processors) it will optimize any Mac running System 7--including 68000 Macs like the Plus, SE, or Classic; Macs with third party accelerators; and the new Power Macs.
  • Unlike the other memory upgrade methods, RAM Charger works on a per-application basis--so you can easily specify optimization for some applications and not others. This allows you to use any combination of optimized and unoptimized applications simultaneously. Other software methods require you to disable the product and restart the computer in order to use any software which doesn't work well with it.

Introduction to Software Memory Upgrades

First let's clarify some terms used. The logical memory space in a Macintosh is what is seen by the user (for example, in the About This Macintosh window), or by the application software. This logical memory space is usually equivalent to what is provided by the physical or hardware memory (often referred to as RAM). The logical memory is most easily expanded by installing additional physical memory and maintaining the usual one-to-one mapping between physical and logical space.

Providing a logical space that is larger than the physical memory requires a selective mapping of blocks of physical memory into the logical space. This differentiation of logical and physical memory access and the mapping between the two spaces is commonly called virtual memory. (The resulting logical space is also called the virtual address space.) As can be imagined, the constant address lookup and translation necessary to support such a scheme has considerable processing overhead. Therefore, it is only used on Macs that have special memory mapping hardware in their processors, to minimize this overhead.

With the standard Mac virtual memory, the extra blocks of logical memory (which are not mapped to physical memory at a given point in time) are stored on disk and swapped with other blocks in physical memory when the processor must access them. However, virtual memory can be implemented using other methods of storing the swapped-out blocks, such as the in-memory compressed buffers used by RAM Doubler.

Using these terms, we define the fundamental difference between RAM Charger and other methods of getting more useful memory as this: RAM Charger optimizes allocation of the logical memory space but does not expand the logical space. The alternatives do the opposite: they expand the logical memory space but do not optimize the use of it.

This might be confusing when examining virtual memory techniques for implementing a larger logical memory space. The virtual memory manager (as provided by the system or by a third party product like RAM Doubler) uses a block replacement strategy to minimize swapping data. This could be described as optimizing the allocation of physical memory, but is more commonly called a memory policy or a paging algorithm. An important thing to notice is that this applies to the allocation of physical memory rather than the logical space, dealt with by applications, that RAM Charger optimizes.

The Benefits of RAM Charger Technology

Optimized applications open using minimum sized initial partitions, but are not limited to them. They use additional memory only where and when they need it (for example, when opening or expanding documents, printing and checking spelling), and each application has access to all the free memory on the machine. When an app releases memory no longer being used (for example, when closing a document or finishing printing), it is immediately available for reuse by other programs--including optimized applications that are already open.

Since RAM Charger optimizes the logical memory space, in contrast to expanding it, RAM Charger is compatible with and works very well with the other methods for getting more usable memory (such as virtual memory and RAM Doubler). Jump Development Group has done a lot of testing with RAM Charger and RAM Doubler and finds they work extremely well together, without any downside. The technologies are entirely different. RAM Doubler uses virtual memory techniques to expand the logical memory space, and then RAM Charger is happy to optimize allocation of the increased logical space provided. And, in fact, the two together give you much more useful memory than either one alone.

So, the two products really complement each other: RAM Charger provides the reduction of initial application partitions and dynamic resizing of apps, while they remain open, so you get more into the memory you have. RAM Doubler compresses your in-memory data and maps in additional virtual address space, so you have more to allocate in the first place.

Since RAM Charger works on any Mac running System 7, it is able to provide benefits for all Mac users, including those unable to use virtual memory expansion for one reason or another. (Virtual memory and RAM Doubler can only be used on machines with the memory man agement hardware.) RAM Charger is the only way to more useful memory for millions of Macs, including all the 68000 machines like the Pluses, SEs, and Classics--or for any Mac which is already at the limit of its physical memory capacity. Even Macs with third party ac cel era tors and Power Macs can benefit from RAM Charger.

The owners of many Macs with memory limitations have held off upgrading to System 7 because of the additional memory demands. Now, with RAM Charger, these people can upgrade to the latest system and application software, keep multiple major applications open at the same time, and still have enough memory to work productively.

No memory upgrade is 100% compatible in all situations (yes, even adding physical memory can cause problems for some configurations of hardware and software). Unlike the other techniques, RAM Charger applies its improvements on a per-application basis. That means it can be turned off for some applications while it continues to optimize others. This allows you to use any combination of optimized and unoptimized applications simultaneously. Virtual memory and RAM Doubler require you to stop what you're doing, close/quit all of your work and restart the computer with the expanded space completely disabled in order to use any product which doesn't work well with them.


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Copyright © 1995-98 Jump Development Group, Inc. All rights reserved. Jump, OptiMem, RAM Charger, and More About This Mac are trademarks of Jump Development Group, Inc. Apple and Macintosh are registered trademarks of Apple Computer, Inc. All other trademarks are the property of their respective holders.