<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; color: rgb(0, 0, 0); font-size: 14px; font-family: Calibri, sans-serif;"><div>Chris,</div><div><br></div><div>A bit of Googling showed that the 137 byte physical sector size came from The Altair 88 disk controller.</div><div>Search for 'Altair 88 dcdd disk controller 137’</div><div><br></div><div>HTH</div><div>Ton</div><div><br></div><span id="OLK_SRC_BODY_SECTION"><div style="font-family:Calibri; font-size:11pt; text-align:left; color:black; BORDER-BOTTOM: medium none; BORDER-LEFT: medium none; PADDING-BOTTOM: 0in; PADDING-LEFT: 0in; PADDING-RIGHT: 0in; BORDER-TOP: #b5c4df 1pt solid; BORDER-RIGHT: medium none; PADDING-TOP: 3pt"><span style="font-weight:bold">From: </span> Simh <<a href="mailto:simh-bounces@trailing-edge.com">simh-bounces@trailing-edge.com</a>> on behalf of Chris Van Brederode <<a href="mailto:cvanbrederode@gmail.com">cvanbrederode@gmail.com</a>><br><span style="font-weight:bold">Date: </span> Friday 21 August 2015 18:45<br><span style="font-weight:bold">To: </span> <<a href="mailto:simh@trailing-edge.com">simh@trailing-edge.com</a>><br><span style="font-weight:bold">Subject: </span> [Simh] Odd Question on CP/M and sector sizes<br></div><div><br></div><div dir="ltr">Hello,<div><br></div><div>I'm working on coding my own 8080 emulator (as an exercise/hobby) and I've gotten to the point where I need to build BIOS for CP/M. I'm looking at using a SIMH based Altair emulator to build the CP/M for my system.</div><div><br></div><div>I have a weird question though. All the documentation I can find on CP/M and floppies from that era point to a 128 byte sector size. But the source code in simh/Altair/altair_dsk.c (and also in the AltairZ80 source), the sector size is given as 137 bytes.</div><div><br></div><div>Looking at this makes me cock my head like a dog. What is up with the extra 9 bytes? Where do they go when the fdc reads a 128 sector to memory for CP/M 3?</div><div><br></div><div>Sorry if I sound ignorant, but I've actually tried to research this, but the only place I can find that mentions 137 byte sectors is the source file, and one post on this list that mentions that it is 137 bytes but doesn't say anything beyond that.</div><div><br></div><div>Thanks for any help,</div><div><br></div><div>Chris</div></div>
_______________________________________________
Simh mailing list
<a href="mailto:Simh@trailing-edge.com">Simh@trailing-edge.com</a>
<a href="http://mailman.trailing-edge.com/mailman/listinfo/simh">http://mailman.trailing-edge.com/mailman/listinfo/simh</a></span></body></html>