Databases
StackOverflow2013
Postsdbo
PO
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PO
    primarykey
    data
    text
    <p>MSDOS FAR pointers had problems like this, which were usually covered over by "clever" use of the overlap of the segment register with the offset register in real-mode. The effect there was that the 16-bit segment was a shifted left 4 bits, and added to the 16-bit offset which gave a 20-bit physical address that could address 1MB, which was plenty because everyone knew that noone would ever need as much as 640KB of RAM. ;-)</p> <p>In protected mode, the segment register was actually an index into a table of memory descriptors. A typical DOS extending runtime would usually arrange things so that many segments could be treated just like they would have been in real mode, which made porting code from real mode easy. But it had some defects. Primarily, the segment <em>before</em> an allocation was not part of the allocation, and so its descriptor might not even be valid. </p> <p>On the 80286 in protected mode, just loading a segment register with a value that would cause an invalid descriptor to load would cause an exception, whether or not the descriptor was actually used to refer to memory.</p> <p>A similar issue potentially occurs at one byte past the allocation. The last ++ on the pointer might have carried over to the segment register, causing it to load a new descriptor. In this case, it is reasonable to expect that the memory allocator could arrange for <em>one</em> safe descriptor past the end of the allocated range, but it would be unreasonable to expect it to arrange for any more than that.</p>
    singulars
    1. This table or related slice is empty.
    1. POWhat C compilers have pointer subtraction underflows?
      singulars
      1. PTQuestion
    1. PTAnswer
    1. This table or related slice is empty.
    1. USRBerteig
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    3. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    1. COhttp://www.faktoider.nu/640kb_eng.html :)
      singulars
      1. PO
      1. USunwind
    2. COThanks for that... you will notice that I didn't quote the phrase or blame Bill for it. It may not really have been said by anyone in seriousness, but the attitude was not unfamiliar to anyone who had to *pay* for a large block of memory....
      singulars
      1. PO
      1. USRBerteig
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload