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A disk made of memory, brought up by whoever owns it

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THE MACHINE SUPPLIES BLOCKS AND SAYS WHAT A DRIVE IS. It says nothing about
filesystems, which is what leaves room for a system that would rather have
its own - and is why the volatile bit is a fact about the hardware rather
than a promise about SBFS.

  0x26        what the selected drive is: bit 0, contents do not survive
  0x27, 0x28  how many blocks it has
  --ram-disk N   a drive of N blocks with memory behind it

A drive of memory selects, reads, writes and has a size like any other, and
a program cannot tell the difference except by how fast it was. The one
thing it cannot work out for itself is that the contents are volatile,
because an empty disk and a volatile disk look identical from outside.

THAT BIT IS THE DIFFERENCE BETWEEN A DRIVE A SYSTEM MAY FORMAT ON SIGHT AND
ONE IT MUST NOT. CosmOS formats a volatile drive it cannot read, because
there was never anything on it to lose, and leaves every other unreadable
drive alone - an unformatted floppy is not an invitation, it is a blank
floppy. Removing that check formats somebody's blank disk, which is checked
rather than asserted: cosmosBlankDisk boots with one and requires it to be
refused.

So CosmOS grew a format. The size comes from the drive rather than from a
superblock, since a superblock states a size too and that is no use on a
disk which has not got one yet. Sixteen directory blocks, 128 names, chosen
rather than worked out: a scratch disk runs out of names long before room,
and this machine cannot divide.

The RAM disk is no faster on this emulator by default, and that is honest
rather than disappointing: the emulated disk has no seek time unless asked
for one. With --disk-cycles 10000 the same copy is 7.94M cycles against
8.70M, the difference being every write.

run.sh takes "ram:2048" where an image name goes, which needs no removing
between runs because there is nothing to remove.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01E2JrLzFvuFX9fgi1LDRjrW
This commit is contained in:
Anachronaut
2026-08-31 17:56:41 -04:00
co-authored by Claude Opus 5
parent 6b51d6391f
commit 04f1ffabd4
15 changed files with 351 additions and 6 deletions
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Source/Emulator/machine.c
+6
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@@ -197,6 +197,12 @@ uint8_t machineStart(Machine *m, const EmulatorOptions *options, const char *pro
return MACHINE_ERROR;
}
}
// After the images, so the drive numbers a command line asks for are the order it asks
// in. A disk made of memory is still a drive and still has to be brought up by whatever
// system is running; the machine only supplies the blocks.
if (options->ramDisk > 0 && attachRamDisk((uint32_t)options->ramDisk)) {
return MACHINE_ERROR;
}
// The screen starts blank, and starts blank again on a warm restart: video memory is
// the device's, and a reset that left last program's screen up would be a reset that
// did not happen.