Troubleshooting the System Memory

Why is my system taking up so much memory?

What is MODE32? The 32-bit enabler? Do I need them?

How much memory should I allot to my cache?

Why is my system taking up so much memory?

Under system versions earlier than 7.0 or under System 7.x without 32-bit addressing turned on the Mac cannot access more than eight megabytes of real memory. If you have more physical RAM installed, the Mac knows it's present but can't do anything with it. When About this Macintosh (About the Finder in System 6) is selected from the Apple menu, the system reports all the memory it can't use as part of the system memory allocation.

To use the memory you need to install System 7 and turn on 32-bit addressing in the Memory control panel. If you have a Mac with dirty ROMs (a II, IIx, SE/30, or IIcx) you also need MODE32. MODE32 is free from the mythical friendly neighborhood dealer or from this link.

The Mac II also needs the FDHD ROM upgrade to use 4 megabyte or larger SIMMs in Bank A. Without it SIMMs larger than one megabyte can only be put in the second bank of memory on a Mac II. If you're staying with System 6, Maxima from Connectix ($45 street) allows you to use up to fourteen megabytes of real memory and can allocate anything beyond that to a RAM disk.

If you have an LC or an LC II with four megabytes of RAM soldered to the motherboard, you still need to add two four-megabyte SIMM's to reach the ten megabyte maximum imposed by the LC ROM. This means you'll always have two unused megabytes which About this Macintosh and About the Finder report as part of the system memory allocation. Unfortunately there is no current means of accessing this extra memory.

If you've turned on 32-bit addressing or if you have eight megabytes or less of RAM, check your disk cache (RAM cache in System 6) in the Memory Control Panel (General Control Panel in System 6) to make sure it isn't set exceptionally high. All memory allotted to the cache comes out of the System's memory allocation.

Finally, if you recently upgraded to System 7.1 by updating your system software rather than by doing a clean reinstall, you should move all fonts out of your system file as these can take up an extraordinary amount of memory.

What is mode32? The 32-bit enabler? Do I need them?

MODE32 and the 32-bit enabler are system extensions that allow Mac II's, IIx's, IIcx's, and SE/30's to access more than eight megabytes of real memory under System 7. The 32-bit enabler is buggy and doesn't work at all with System 7.0 or 7.5. If you have more than eight megabytes of real memory in an SE/30, II, IIcx, or IIx, (or eight megabytes and RAM Doubler) you need MODE32. Get it here!

How much memory should I allot to my cache?

ne of the Memory Control Panel (or General Control Panel in System 6) settings is the mysterious cache -- Disk Cache in System 7, RAM cache in System 6. This is memory the system sets aside to hold frequently accessed data from the disk. The cache acts like a 7-11 for your hard disk. It's quicker to get a quart of milk at the 7-11, but it costs more so you don't do all your shopping there. And the 7-11 doesn't have everything you want so sometimes you need to go to Safeway (your hard disk) instead.

Unfortunately the caches in pre-7.5 system software really aren't all that fast. For most people the RAM cache would more appropriately be called the RAM thief. However, there are a few applications and extensions (such as Dayna DOSMounter) that actually make use of the cache and will run much faster when it's turned on than when it's off. Thus I recommend setting your cache to 64K, turning it on, and forgetting about it.

If you're running System 7.5 however, you're in luck. Apple rewrote the caching software to provide better performance for System 7.5. If you have plenty of RAM (more than 8MB), feel free to create a large cache -- up to a megabyte or so. This should increase both speed and performance.

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Much of the information contained herein has been extracted from Elliotte M. Harold's incredible FAQ lists. We thank and commend him for his invaluable service to the Macintosh world.