9 Mar
2023
9 Mar
'23
6:40 p.m.
removed in PWB/UNIX 1.0.
ifdef'd out in the Harvard/Radcliffe Student Time-sharing System (HRSTS)
parts found in tuhs/Applications/Usenix_77. h/distrib.note includes:
'4. "Huge" files are not supported by our modifications. This is not
necessarily a hard restriction, however we early on decided
we wanted no more than one level of indirection all the way up to 1 megabyte,
and had no need for larger files. The incompatibilities may be minimal,
but we have not even bothered to seek them out.'
On Thu, Mar 09, 2023 at 03:21:19AM -0500, Kenneth Goodwin wrote:
I have not seen the UNIX kernel source code in quite a
while, but as I
recall the double indirect block algorithm did not kick in until the file
exceeded a certain threshold. So it would not make sense to remove the code
for performance reasons.
Perhaps this is more likely due to the use of larger logical block sizes....
Is the code physically removed or IFDEF'd out for conditional compilation?
Perhaps someone decided that programmers would never need to test code on
large files..
On Wed, Mar 8, 2023, 8:10 AM Noel Chiappa <jnc(a)mercury.lcs.mit.edu> wrote:
> In PWB1, support for 'huge' files appears to have been removed. If one
> compares bmap() in PWB1'S subr.c with V6's, the "'huge'
fetch of double
> indirect block" code is gone. I guess PWB didn't need very large (>
> 8*256*512
> = 1,048,576 bytes) files? I'm not sure what the _benefits_ of removing it
> were, though - unless PWB was generating lots of files of between 7*256*512
> and 8*256*512 bytes in length, and they wanted to avoid the overhead of the
> double-indirect block? (The savings in code space are derisory - unlike in
> LSX/MINI-UNIX.) Anyone know?
>
> Noel
>