- Original Message -
From: ZN [EMAIL PROTECTED]
To: [EMAIL PROTECTED]
Sent: Thursday, July 14, 2005 2:53 PM
Subject: Re: [ql-users] Size for QXL.win Files
On 08/07/05 at 11:23 P Witte wrote:
John Gilpin writes:
4Gb per QXL.win file...
I only get 2GB with QPC2: FORMAT win8_4000 fails while win8_2000 doesnt.
Even then the file allocation block is a massive 32k. It seems to me that
4GB must be the theoretical limit for the current mapping scheme. The
minimum space taken by a file on disk would then be a whopping 64k
Per
Per is right, IIRC QLWA may have a 2G limit, even though 4G would be the
theoretical maximum.
There are two possible reasons for it:
1) Maximum number of allocation blocks (think of them as a sort of
super-sector) is a 16 bit word, unfortunately, some implementations and
versions took it a s a signed integer instead of unsigned.
2) Maximum size of one allocation block is a 16 bit word, again some
implementations and versions used signed arithmetic to point to a byte
within the block, which reduces it's maximum size to 32k.
IIRC the first error is the more likely to crop up. When QUBIDE was being
maintained, these cropped up, but I do not remember the speciffics any
more.
4G is a sort of double limit as the system implies that the whole QLWA
partition can be used up by a single file. Since the file pointer is a 32
bit unsigned (hopefully!) integer, the maximum size of a file is 4G, and
so
is the size of the partition (64k blocks each 64k in size = 4G).
The serious limitiation here is that one file always takes up at least 1
allocation block (even if the file is empty!) and the less serious one is
that there can be max 64k files. The first is quite restrictive in QL
terms
as files are, in general, much shorter than 64k. This produces a lot of
wasted space.
If you want to be absolutely sure, 1G QXL.WIN, with 32k allocation block
size is the way to go, it avoids all the possible pitfalls...
Nasta
Thanks for the advice, Nasta, and all explained so that I can follow the
reasoning. I will do a bit of experimenting but the comments received as to
what should be theoretically achievable is a great help.
John Gilpin.
___
QL-Users Mailing List
http://www.q-v-d.demon.co.uk/smsqe.htm
