allyn@sdcsvax.UUCP (Allyn Fratkin) (02/26/86)
I have some questions about disk interleaving. What is the default
interleave of the hard disks in IBM PC ATs and XTs? I have heard that
the default interleave is much too low, around 2 or 3, and that disk
performance can be signifigantly increased by reformatting with
a higher interleave.
I would really appreciate it if someone could clear this up for me.
--
From the virtual mind of Allyn Fratkin allyn@sdcsvax.ucsd.edu or
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"Generally you don't see that kind of behavior in a major appliance."langet@ecn-pc.UUCP (Timothy Lange) (02/27/86)
The 10 Mbyte drives in the IBM PC/XT when shipped by IBM are formatted
with 512 byte sectors at an interleave factor of 6 (17 sectors per
track, 4 heads per cylinder).
The above is from page 8-8 of the DOS Technical Manual.
--
Tim Lange Engineering Business Offices
317-494-5338 Rm 120 Engineering Administration Bldg.
Purdue University West Lafayette, IN 47907
{decvax|harpo|ihnp4|inuxc|seismo|ucbvax}!pur-ee!langetgst@talcott.UUCP (Gary S. Trujillo) (03/03/86)
In article <1480@sdcsvax.UUCP>, allyn@sdcsvax.UUCP (Allyn Fratkin) writes: > I have some questions about disk interleaving. What is the default > interleave of the hard disks in IBM PC ATs and XTs? I have heard that > the default interleave is much too low, around 2 or 3, and that disk > performance can be signifigantly increased by reformatting with > a higher interleave. > > I would really appreciate it if someone could clear this up for me. The subject of disk interleave factors, as well as other technical goodies about such things as cluster sizes and encoding techniques are covered very nicely by Marcus Kolod in his article (p. 283) in the Fall 1985 issue of Byte in his article entitled "IBM PC Disk Performance and the Interleave Factor." (The same issue contains a couple of additional articles on hard disks on the AT.) He concludes the article, which contains diagrams and tables showing the effects of diddling the various things one can diddle when formatting hard disks, shown both for the XT and the AT, by saying: Did IBM choose the best interleave? There is a discrepancy between the stated interleave (6) in the DOS 2.0 manual and the interleave that both showed the best times in my test and matched the interleave of a brand new XT from IBM, namely, 7. Considering that, I think the answer is yes for both machines. IBM has optimized its code around single-sector reads. Although DOS may intermittently perform multiple-sector reads, it primarily accesses single sectors. If multiple-sector reads are performed, it does appear that better interleaves exist. -- Gary Trujillo (harvard!talcott!gst)