Power Macintosh Native Applications Need Connectix RAM Doubler
Topics Covered:
･ Memory Usage of Power Mac Native Applications and File Mapping
･ RAM Doubler File Mapping Example - Microsoft Excel 5.0 for Power Macintosh
･ File Mapping: RAM Doubler vs. Virtual Memory
･ How to Contact Connectix
Power Mac native applications use less memory with RAM Doubler installed. By using a memory management technique known as file mapping, RAM Doubler reduces the memory footprint of all native applications. This memory savings is in addition to the doubling of memory RAM Doubler provides. With this twofold benefit, RAM Doubler is the best way to optimize Power Mac memory usage and get the most out of installed RAM. This document briefly describes the file mapping memory management technique utilized by RAM Doubler and its importance for Power Mac native applications.
RISC (PowerPC) processors are optimized to handle a smaller number of instruction types as opposed to CISC processors (68k). Because of the faster processing speeds achieved by the reduced instruction set, programs run much faster. One minor drawback to RISC processors is that they take more instructions to perform the same amount of work (about 33%, on average). Fortunately the speed benefits far outweigh this small increase in code size. But this code size increase requires more RAM. Thus, native Power Mac applications require a larger amount of memory to perform the same function as its 68k equivalent. Moreover, the faster processing speed of PowerPC chips has encouraged developers to add additional features to their products. In many cases, the memory requirements for native applications grow to several times the size of their 68K equivalents.
These memory requirements are reduced by using the file mapping memory management technique Apple built into the Power Mac ROM. File mapping is used whenever Connectix RAM Doubler is installed or System 7 virtual memory is enabled. In fact, using one of these two products is the only way you can get file mappingﾕs benefits.
Without file mapping, native applications load their entire code base, often several megabytes worth, into application memory. File mapping works by loading into memory only the application code being used, leaving additional application code on the hard drive to be swapped into memory as necessary. This significantly reduces the amount of memory used by native applications. To find out how much memory is being saved by file mapping, do a ﾒGet Infoﾓ on a native application with RAM Doubler running.
The best way to illustrate the difference RAM Doublerﾕs file mapping will make on a native application is to compare memory requirements without RAM Doubler to memory requirements with RAM Doubler installed. This example uses Excel 5.0 for the Power Macintosh.
RAM Doubler Not Installed
Launching native Excel 5.0 on an 8MB Power Macintosh:
ﾊ
ｷ 4MB of memory for the Excel default partition (can be changed by the user via ﾒGet Infoﾓ under the systemﾕs File menu when large spreadsheets are being used).
ｷ 6MB of memory for Excel data fork (a fixed number based on code size).
ｷ 3.5MB of memory for the code contained in shared libraries used by Excel on the Power Macintosh (fixed number based on code size). Having code in a shared library means it is only in memory once, even when used by multiple applications.
This adds up to a grand total of 13.5MB of physical memory required to start Excel when extended memory is off. Thus, even a PowerMac with 16MB RAM (assuming System Software uses 4MB) will not have enough memory to launch Excel 5.0.
RAM Doubler Installed
Launch native Excel 5.0 on an 8MB Power Macintosh:
ﾊ
ｷ 4MB of memory for the Excel default partition (can be changed by the user via ﾒGet Infoﾓ).
ｷ All code will be ﾒdemand pagedﾓ through RAM Doubler file mapping so no memory is required in the set partition for Excel code and the shared libraries.
This adds up to a grand total of 4MB of logical memory required to boot Excel with RAM Doubler installed. By using RAM Doubler, there is a dramatic reduction in Excel 5.0 memory demands, from 13.5MB to 4MB. Suddenly, a 16MB Power Mac has not enough room to run Excel, but to run additional applications, as well. Plus, in addition to the memory savings, RAM Doubler doubles the amount of memory installed, providing room for more applications to be run. With the twofold benefit of file mapping and RAM expansion, RAM Doubler is the best way to optimize Power Mac memory usage and get the most out of installed RAM.
File mapping is essential to reduce memory demands of native applications. Power Mac file mapping is enabled through two methods: Connectix RAM Doubler and System 7 virtual memory. While both provide the file mapping benefit, RAM Doubler performs faster and saves valuable hard drive space over System 7 virtual memory.
Apple Computer, as of January 1995, ships every new Power Macintosh model with virtual memory turned on to the amount of physical RAM plus one megabyte. On a 16MB configuration, for example, virtual memory will be set to 17MB. The primary benefit of virtual memory on the Power Mac is file mapping. The cost of virtual memory on the Power Mac is 1) a 10 to 15% performance penalty and 2) drive space usage equivalent to the total amount of memory (in our example, this amount is 17MB). Apple provides a document (entitled ﾒAbout Virtual Memoryﾓ ) on the root level of the hard drive of every new Power Mac to explain file mapping and virtual memory usage to new Power Mac customers.
By using RAM Doubler instead of Appleﾕs virtual memory on a Power Mac, the benefit of file mapping is gained without the cost of performance or hard drive usage. RAM Doubler causes no discernible performance degradation (typically about 1 to 3%) and usually requires no hard drive space to double any configuration of 8MB RAM or greater. In addition, RAM Doubler exactly doubles the amount of application memory to run more applications. Letﾕs look at RAM Doublerﾕs benefits over System 7 virtual memory more closely:
･ Improved performanceﾑSystem 7 virtual memory slows your Power Macﾕs performance 250% or more than does RAM Doubler
･ More hard disk spaceﾑSystem 7 virtual memory uses 16-17MBs more hard disk space than does RAM Doubler in standard configurations, and it gets worse as you increase the virtual memory size!
･ More application spaceﾑRAM Doubler provides double the application memory, where the System 7 virtual memory configuration Apple ships provides only a megabyte of extra space (while you can up this amount, performance decreases and more hard disk space gets chewed up with System 7 virtual memory)
Compare a Power Mac with RAM Doubler installed to a Power Mac with virtual memory enabled: The RAM Doubler Power Mac is faster, has more drive space available, and exactly doubles the memory ﾑthere is no comparison.
Memory requirements for Microsoft Excel 5.0 from the Microsoft Strategic White Paper - Power Macintoshｪ Technology: Microsoft Office 4.2 for the Macintoshｨ; Part Number 098-56876, October 1994. This document is available from Microsoft Sales Fax Service at (800) 727-3351.
