19 Apr
2003
19 Apr
'03
9:26 a.m.
A rule of thumb I use, but I won't swear is
universal... Is the LED color. USUALLY... Red LED
signifies 360k/180k Drives, and a Green LED signifies
1.2mb Drives.
Again, not reliable. The 1.2M drive on this machine (orginal IBM) has a
red LED. I think that for Teac drives, the LED colour was actually a
customer-selectable option (red, yellow and green all exist, for all
types of drives)
And I also think that as for IBM Drives, the 360k at
one point were made with and Asterisk molded into the
front case. I could have this reverse. But, I seem to
remember some discussion (perhaps here) that someone
thought it was odd that IBM would start adding the
asterisk to 360k Drives, hence having some with and
some without, rather than just making all 1.2mb drives
with asterisks.
It's more complicated than that. There are 2 types of IBM 360K
half-height drives. The one that was used in the PortablePC and the PCjr
does _not_ have the asterisk. The one that is used in the PC/AT does. The
2 drives have other differences too -- they were made by different
manufacturers normally (the PortablePC / PCjr one is a Qume, I forget who
made the one for the PC/AT), and I suspect pin 34 changed between Ready
and DiskChange.
No IBM 1.2M drive has the asterisk.
This is really stupid (as others have pointed out) -- it would have been
much easier and clearer to mark the 'new' type of drive -- the 1.2M one.
Also, if you look at the jumpers on the logic board,
near the drive select jumpers... A 1.2mb drive should
have a Speed Select Jumper (SS) to select High speed
Data Transfer to work on AT-Standard Floppy
Controllers, and low speed (for what? I don't know...
Maybe to work on an 8in Drive Controller?)
No, the 8" controller would have wanted the higher speed too (360rpm).
IBM controllers always spun the 1.2M drive at 360rpm, which means they
had to support a 300kbps transfer rate (==(360/300) * 250kbps) for 360K
disks in 1.2M drives. The lower speed (almost never used) was to allow
360K disks to be read at 250kbps on a suitable controller.
However, this jumper is also not a reliable indication of drive type.
Many later drives have almost no jumpers at all, and SS would be one of
the first to vanish as almost nobody used it. So there are 1.2M drives
around without the jumper.
And some manufactuerers used common logic boards and even spindle motor
PCBs for 360K and 1.2M drives. Which means there are 360K drives out
there with the SS jumper.
-tony