Subject: 3.5" & JRCONFIG.SYS-Edited & Copied from PCJR Forum
Note: First see 2NDDISK.TXT on PCjr Toolkit diskette 
Modified Crumley 2nd drive as follows:
 
Placed additional twist in cable between diskette adapter card and
internal 5.25" drive. Thus making internal drive 2nd (B) and external
drive 1st (A).
Placed 36 pin (Centronics Female Ribbon cable type) connector at end
of cable (at 2nd original twist).
Placed 2 drives in powered box with "Y" power adaptor cable. (at no
time will both drives be fully powered simultaneously).
Brought out two ribbon cables from each drive to a 36 pin (Centronics
Male Ribbon cable type) connector. (note: last four pins on connectors
not used)
Result: Can boot off either a 3.5" or 5.25" drive as external drive A.
        Very easy to manually switch at any time with polarized
        connectors.
        Diskcopy from D to E (720k) works great with two passes
        depending on memory.
 
 No terminator Resistor packs used on 5.25" drives, but terminator
 was left on the 3.5" drive with no ill effects.
 If you don't like the inexpensive manual cable switch, you can
 use a 2-position Centronics (printer) switch box and 3 Female
 connectors. Boxes sell for around $30.00 and are quite heavy.
 
One problem noted:
     1. Copyiijr not only cannot recognize drives beyond A & B,
        but can't handle 3.5" drives.
CONFIG.SYS file:
 1. DEVICE=JRCONFIG.SYS -D2 -C -V32 -S91 -T3
               (Assigns 1st drive as A, 2nd drive as B and 91K lowmem
                C ram disk with no phantoms)
 2. DRIVPARM=D:0 /F:2
               (From Computer Shopper-Undocumented DOS-To Format A-720k)
 3. DEVICE=DRIVER.SYS /D:0 /F:2
               (Sets 1st drive to a 720k D drive)
 4. DEVICE=DRIVER.SYS /D:0 /F:2
               (Sets 1st drive to a 720k E drive so I can copy D to E)
RESULTS:
    Drive A is 1st (3.50") with max 720k access. (can format to 720k)
    Drive B is 2nd (5.25") with max 360k access.
    Drive C is a 91k low-memory ram disk
    Drive D is 1st (3.50") with max 720k access. (formatable)
    Drive E is 1st (3.50") with max 720k access. (formatable)
 
In my search for a usable 3.5" driver for DOS 2.1, I came across
Mach 3.5 from J & M Systems in Albuquerque ($29.95 + S&H).
Function is very similar to Driver.sys with a special FORMAT35
for the D & E drives (as above). Problem is you cannot boot from a
720k diskette (DOS 2.1 can't read it!). The 3.5" disk in drive A
must be formated as a 360k disk to boot. Also it can be quite
dangerous to move data from a 3.5" 360k to a 3.5" 720k unless you
have a third drive or religiously write protect,
as no "phantom" pause occurs in which to change
the disk. The FAT & directories will be destroyed.
 
 Henry F. Kennedy    Tie 678-6366        (HKENNEDY)AUSVM7