New Commodore 64 is Finally Here--For Real! PC MAG Snip
cisin at xenosoft.com
Fri Jan 1 15:28:54 CST 2016
>> While, at the time, 2G seemed "infinite", even then, I was amused at the 2G
>> limitation being due to the use of a SIGNED 32 bit number. The size can be
>> anywhere from -2147483648 to 2147483647.
>> By switching to an UNSIGNED 32, NT and the like made the limit 4G.
On Fri, 1 Jan 2016, Jim Brain wrote:
> I think it was actually the sectors per cluster number, which was -64 to 63,
> I believe and then got changed to 0-128, meaning cluster sizes of 128
> 512-byte sectors, or 64K clusters
Quite likely more than one place with limits. It seems likely.
There was probably a tendency to treat all numbers as signed.
I do know that the 32 bit file size field in the DIRectory entries was
processed by some DOS operations, including DIR as a signed number.
Replacing those four bytes with FF FF FF FF would result in a reported
file size of -1 bytes. Replacing it with 00 00 00 80 (LSB first) gave a
reported file size of -2147483648
> I know folks will hate on the format, but I am extremely impressed with the
> FAT format. To go all the way from floppies to 4TB drives is impressive.
I think that it is just fine. I prefer it over a list of blocks, that
might result in needing multiple directory entries, such as CP/M or
TRS-DOS. I much prefer it over the need for contiguous space
Even the original Macintosh disk format was essentially the same
algorithms as MS-DOS FAT.
Besides MS-DOS, Microsoft made some "Stand-Alone BASIC" designs that used
the same idea of DIRectory and separate linked list. Albeit at seek
center instead of track 0. Radio-Shack Color Computer, NEC, Okidata,
etc. I've even seen a disk from a Russian computer with that type of
Some of the histories of MS-DOS say that Tim Paterson, in building his
QDOOS ("Quick and Dirty OS") place-holder while waiting for CP/M-86, got
the idea for FAT from seeing Microsoft Stand-Alone BASIC "for NCR" at
Microsoft's West Coast Computer Faire booth. I was at that show, and saw
NEC machines with it, but I've never seen an NCR Stand-Alone BASIC - did
the histories goof?
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