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"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)?"
Summary
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.
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- 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.
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- 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.
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- 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.
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- 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.
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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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