RAM in the LCs, addressing and RAM disk

Bigger, Higher, Faster

The LCs have oft been berated for having a small memory capacity. The LC and LCII especially are reknown for having a rather minimalist memory ceiling of 10MB, not overly stunning at the best of time but it was enough for the market the LCs were aimed at in their day. There is no real way to increase this limit as it is imposed by the memory controller as far as I know.
The LCIII/+ and LC475 however have a higher memory ceiling of 36MB, according to their specification. The LCIII/+ will not go above 36MB as the memory controller will not go any higher. The LC475 however can be upgraded beyond this limit, how is another matter.
I currently am still looking into this matter and will report further on my finidings. In the mean time this article at LowEndMac should answer most queries, at least on 64MB SIMMs.

RAM Addressing and the LCs

All the LCs use 32-bit 'clean' ROMs and so can be set to use 32-bit memory addressing. This means they can address more than 8MB of RAM straight out of the box with no extra extensions, such as Connectix Mode32. This must, however, be turned on by the user in earlier versions of Mac OS 7. Diagnostic symptoms of this are, when looking at the 'About this Mac...' dialog, the System item takes up more than 2-3MB of memory. If you have 36MB installed on an LCIII and the System seems to be taking up 30MB then this is the problem. To enable 32-bit addressing in System/Mac OS 7 you should to the Memory Control Panel and toggle the 32-bit option to 'On'. This is only applicable in versions previous to 7.6 as 7.6 will only run on 32-bit machines, it does not supprt those with 24/32-bit 'dirty' ROMs.

RAM Disk on LCs

The Macintosh LC is not capable of running a RAM disk using the Apple RAM Disk option in the System/Mac OS 7 control panel. It does not meet Apple's miinimum specification for a machine to run RAM disk. The LCII and newer machines will run Apple RAM Disks. This can be enabled by openeing the Memory Control Panel and selecting 'On' in the RAM Disk section. You shoul'd then define what proportion of the machine's total RAM you wish the RAM Disk to occupy, this is expressed as a percentage of the total RAM on a slide bar.

There are also third party solutions for RAM Disks. These often enable RAM disk on older machines not capable or running and Apple RAM Disk, such as the Macintosh LC. They also add many other features that are not offered by Apple's RAM Disk option. I am currently using Connectix Maxima on my LCIII hybrid machine. It copies the contents of the RAM Disk to the hard disk on shut down and automatically re-loads them at boot time so you can fill it up and, provided you leave sufficient space on the hard disk, it will be there whenever you start the machine. There is also a utility called Rambunctions that will do similar things but I have not used it as yet. Copies of the Connectix Maxima package can likely be found on eBay or the LowEndMac swap list.

Video RAM in LCs

The Macintosh LC and it's revisions were the first consumer machines to have upgradable Videro RAM (VRAM). This allowed them to be upgraded to display higher video resolutions (up to 1024x768 on the LC475) and greater colour depths (up to Millions of Colours). The various models all have practically the same video controller, but have differing VRAM limits as the machines became better. The LCIII and LCIII+ were the only models to have any permanantly affixed VRAM on the logicc board, 256k in both cases, and the other models had slots only. The slots on all LCs are the same allowing VRAM to be passed on to newer machines as they are upgraded. All the machines will take either 512k or 256k VRAM SIMMs at 80ns or faster speed. Perhaps the most impressive feat of the LCs is the LC475's ability to handle up to 1MB or VRAM, allowing it to run a screen at at 832x624 with a colour depth of Millions of Colours.