len@netsys.COM (Len Rose) (12/30/88)
I have to assume it's just a driver loaded that enables the controller to access the extra cylinders.. I always thought that the controller chip was the limitation..I am trying to get a data sheet on the controller (NEC 7261) for another project .. I might guess that also like the original driver, Congruent may be stealing an unused bit somewhere on the controller chip.. Until I see a data sheet,no way to tell. The project I mentioned was re-doing the driver so that one could have 4 drives * running off the internal controller (4 drives each 8 heads/1024 cyls) without having to resort to adding expansion disk controllers. The hardware is there already,and I suspect the driver should be easy. I believe there was some mention of this in an old issue of the 3B Journal,but I don't remember which issue. * Example: Micropolis 1325 (8 hds/1024 cyl)
friedl@vsi.COM (Stephen J. Friedl) (01/02/89)
In article <806@ttrde.UUCP>, pfales@ttrde.UUCP (Peter Fales) writes: > > The earliest models of the 3B2/300 (possibly 310?) did only support disks > with eight heads or less. The following simple modification will > allow an early model 3B2/300 to use more than eight heads: > > [simple mod deleted] I can provide some additional information on the 3B2 hard disk system that might help with some understanding here... The disk controller chip on the 3B2/{300,310,400} is the NEC 7261, and it has two drive-select lines plus three head-select lines. Fully decoded, this provides four drives of eight heads each. The CDC Wren II drives that AT&T uses have *nine* heads, so AT&T -- in the 310, at least -- decided to use one of the drive select lines as a head select. So, the controller can now talk to two drives, each having sixteen heads. You may imagine that the driver software has to do some odd stuff to make this happen, and you're not too far off. >>>>> the following is *total* speculation on my part. <<<<< I would guess that Peter's mentioned modification is doing what is described above -- routing the controller's second drive-select line to the interface's fourth head-select. When they came out with the /310 and the /400, this modification was part of the standard system. I would also speculate that this mod won't work on an original /300 with original software, because the drivers would not have known how to do the diddling with the lines -- everything since (at least) SVR2.0.4 has it standard in the IDISK driver. Steve -- Stephen J. Friedl 3B2-kind-of-guy friedl@vsi.com V-Systems, Inc. I speak for me only attmail!vsi!friedl Santa Ana, CA USA +1 714 545 6442 {backbones}!vsi!friedl -------Nancy Reagan on Usenix in San Diego: "Just say *go*"-------