On Tue, 9 Apr 2002, Cameron Kaiser wrote: I have a PCjr with an add-on 3.5" disk drive chassis. You take the cover off the PCjr case, then stack this unit on top, then place the lid on top. I can't remember if it replaces the existing disk controller with something else. Sellam Ismail Vintage Computer Festival ------------------------------------------------------------------------------ International Man of Intrigue and Danger http://www.vintage.org * Old computing resources for business and academia at www.VintageTech.com *

On Tue, 9 Apr 2002, Cameron Kaiser wrote: ANY! DOS!, NOT WINDOZE 3.10 or above; NO WINDOWS95. But each successive version of DOS was bigger. If you don't further expand the memory, then later ones (5, 6.2x, 7.10, etc.) will be too cramped to have enough space to run most programs. I recommend NOT using anything before 2.00. And, if you use the Qumetrak 142 drive that IBM used, those drives are too slow for 2.00, which is why 2.10 was created. Thus, PC-DOS 2.10 is the ideal version of DOS to use unless/until you expand the memory. If/when you expand the memory to 640K, then I'd recommend running 6.2x. <RANT> 6.2x is the only product in Microsoft's history where the primary design goal was to improve reliability rather than adding bells and whistles. </RANT> Model number is the easiest way (although Tony might prefer tracing the signal from the write-current level pin) If you find a drive with an asterisk on the front, it is a very late model 360K. If there is no asterisk, then it is a 360K, 720K, or 1.2M (there also exist a few "weird" ones) 720K is. 1.4M would require a different disk controller. Although a controller to do 1.2M (5.25") and 1.4M (3.5") could be relatively easily designed and manufactured, I don't recall ever seeing one for the Jr. The 720K is fully hardware compatible with the Jr. You would need to use either special patches to the OS, or use PC-DOS 3.20 or newer (using DRIVER.SYS) When used with the old style mounting brackets, it can bolt in in place of a 5.25. A "dual" or "combo" drive could be used to give you both a 3.5 and a 5.25 in the stock Jr case. The 3.5 would operate as a 720K, and the 5.25 could be used as either 360K or 720K, although I expect that you'd have to write a device driver to get the 360K mode (double stepping) to work, and you'd have to jumper the drive for 300RPM spindle motor speed, since the Jr doesn't provide a 300K data transfer rate to be able to use the 360RPM as the AT did. -- Grumpy Ol' Fred cisin(a)xenosoft.com