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From: ephraim@wang.UUCP (pri=8 Ephraim Vishniac x76659 ms1459)
Newsgroups: net.micro.mac
Subject: Re: Ten Challenges  (long)
Message-ID: <809@wang.UUCP>
Date: Mon, 19-May-86 15:09:50 EDT
Article-I.D.: wang.809
Posted: Mon May 19 15:09:50 1986
Date-Received: Fri, 23-May-86 07:06:27 EDT
References: <21100039@orstcs.UUCP>
Organization: Wang Labs, Lowell MA
Lines: 36

> Ten Challenges:
> ...
> Myers Challenge #3:
>      Every RAMdisk I've seen on a Mac has been terribly primitive.
> Why do they use up space not occupied by files, instead of claiming
> the storage when it is needed?

There are two general ways to allocate storage: permanently, from high memory;
or temporarily, from one of the heaps.	The first can't be done while most
programs are running, since it involves moving the stack.  The second isn't
very useful for a RamDisk.  The system heap is too small and the application
heap is re-initialized at every program launch.

> Further, when a program is run off of a RAMdisk, why is it in memory twice?
> Free up the blocks it occupied and use the core image from then on.

The copy of a file (resource, data segment, ...) in system memory is
*modifiable*.  Even code segments can contain modifiable local data areas.
(No flames about coding styles, folks, it's just an ugly fact of life.)
They also move around at the whim of the memory manager or application.

> Allow files to be copied into RAM when they're first opened instead of
> at startup.

That's a disk cache (exists already) or a memory manager/segment loader
(exists already).

>     The person who builds a smart Ramdisk will own the business.

Let's see here...  Apple built a disk cache, and they built the memory manager.
And - they own the business!

A RAMdisk is an attempt to improve memory management based on the idea that
the user knows better than the system what should be where in the storage
hierarchy.  Mr. Myers isn't asking for a "smart ramdisk", he's asking for
a better memory manager.