Two IDE HDs in One Desktop PC

Hi,
Do to very low activity in the "Hardware" NG, I am posting the
following he

Years ago I had a conversation with a ham radio operator who
told me that he had installed two IDE HDs (Hard Drives) in his desktop PC.
Before he powered up his PC, he would flip a switch (he installed) to
select which HD will boot up. The other is "invisible" to BIOS.

Unfortunately, I had no interest in doing what he did, and I
do not have a record of his call sign since I don't keep a "Log".

Now I have a need to do the same, but I am not sure if
"switching" (by a switch) the power source (+5V, +/- 12V and
+3.3V) will "work"? In effect, the "unused" HD has it's power
cable disconnected, but the IDE data cable is still plugged
in.
Thank You in advance, John N3AOF

Hello John,

Now I have a need to do the same, but I am not sure if
"switching" (by a switch) the power source (+5V, +/- 12V
and +3.3V) will "work"?

Hmmm... I'm not so sure about that being a good idea. Its rather possible
that the unpowered electronics on the drive will allow a current to flow
thru the datalines causing havock with the wave forms, especially at higher
speeds.

But have you already tried if simply changing the master/slave setting on
both drives will work ?

That setting is mostly just the placement/removal of a single jumper, or, if
you are unlucky enough, the movement of that same jumper to another
position.

In the first case it would be a 4-wire thing, with a switch disconnecting
one pair of wires (going to a two-pin connector replacing jumper on the
first drive), and connecting another pair of wires (going to a two-pin
connector replacing jumper on the second drive).

In the second case it would be (at most) an 8-wire thing, disconnecting one
pair of wires and connecting another pair for the first drive and the same
for the second drive.

Mind you, I don't think it would be a good idea to flip this switch when the
'puter is powered ...

Hope that helps,

Regards,
Rudy Wieser


-- Origional message:
wrote in message
...
Hi,
Do to very low activity in the "Hardware" NG, I am posting the
following he

Years ago I had a conversation with a ham radio operator who
told me that he had installed two IDE HDs (Hard Drives) in his desktop PC.
Before he powered up his PC, he would flip a switch (he installed) to
select which HD will boot up. The other is "invisible" to BIOS.

Unfortunately, I had no interest in doing what he did, and I
do not have a record of his call sign since I don't keep a "Log".

Now I have a need to do the same, but I am not sure if
"switching" (by a switch) the power source (+5V, +/- 12V and
+3.3V) will "work"? In effect, the "unused" HD has it's power
cable disconnected, but the IDE data cable is still plugged
in.
Thank You in advance, John N3AOF

wrote:
Years ago I had a conversation with a ham radio operator who
told me that he had installed two IDE HDs (Hard Drives) in his desktop PC.
Before he powered up his PC, he would flip a switch (he installed) to
select which HD will boot up. The other is "invisible" to BIOS.

Unfortunately, I had no interest in doing what he did, and I
do not have a record of his call sign since I don't keep a "Log".

Now I have a need to do the same, but I am not sure if
"switching" (by a switch) the power source (+5V, ± 12V and
+3.3V) will "work"? In effect, the "unused" HD has it's power
cable disconnected, but the IDE data cable is still plugged
in.

The 4 pin molex power connector to the IDE hdd is 12 & 5V (2 ground), no
3.3V. There are switches for that such as:

https://www.coolerguys.com/products/...-12v-and-5v-dc
Molex 4 Pin on/off Power Switch 12V and 5V DC - $ 3.95 USD

That doesn't switch from one to the other, it switches one power source
off or on.

I'm not yet understanding why you want to do 'it', switch from one hdd
to the other with the PS. I would rather do it in the BIOS, which also
would keep the BIOS 'informed' about which of the data routes is in play.

--
Mike Easter

jaugustine wrote:

Years ago I had a conversation with a ham radio operator who told me
that he had installed two IDE HDs (Hard Drives) in his desktop PC.
Before he powered up his PC, he would flip a switch (he installed) to
select which HD will boot up. The other is "invisible" to BIOS.

Unfortunately, I had no interest in doing what he did, and I do not
have a record of his call sign since I don't keep a "Log".

Now I have a need to do the same, but I am not sure if "switching"
(by a switch) the power source (+5V, +/- 12V and +3.3V) will "work"?
In effect, the "unused" HD has it's power cable disconnected, but
the IDE data cable is still plugged in.

Switch might be superfluous depending upon the features inside your
BIOS. Go into the BIOS and check if there are enable/disable options on
the controllers to which the IDE drives are attached. If the IDE drives
are attached to *separate* controllers than you may be able to disable
one controller and leave the other enabled. That would let you switch
between the IDE drives. If the IDE drives are connected to the same
controller (as master and slave) then this method won't work -- unless
you have another IDE controller (i.e., more than 2 IDE ports on the
mobo) to which you could connect the slave drive (then jumpered as a
master drive). Switching between IDE ports in the BIOS only works if
only one drive (as master) is connected to each IDE controller.

Note: Since the IDE drives are found by their BIOS enumeration, you may
have to change the boot.ini file so it correctly identifies the new
physical enumeration of the slave drive you moved to a different IDE
port and made a master.

Instead of using the master/slave jumper setup, some IDE drives let you
use cable select. So I suspect the guy's physical switch would open or
short the CS line on an IDE drive. I doubt he was using a 10-gang
switch to manage all 4 power lines on each drive and the cable select on
both.

Rather than bother with some modified IDE cable and drive jumpering (if
your IDE drives support cable select) or having to go into the BIOS to
switch which IDE controllers are enabled or disabled (which requires 2
reboots: 1 to go into BIOS and another after changing the BIOS to effect
the changes), why not use removable drive bays? Power down and slide in
which drive you want to use. The dock remains permanently installed in
a drive bay in the case. You need a caddy for each drive. Don't bother
with a hotswap dock+caddy since IDE doesn't support hotswap (SATA does).

Why go through the bother of all that hardware? Just use a multi-boot
manager. Some work by usurping the 446-byte bootstrap area of the MBR
(of the master drive). Some want more fancy options than that tiny
space allows; however, that means they have to reside within tracks that
might be allocated to a partition which means any repartitioning will
corrupt that boot manager. In the past, I used GAG The Graphical Boot
Manager. It usurps the 446-byte boot code in the MBR of the master IDE
drive to present to you a menu letting you select from which drive to
boot. Because it was in the MBR, no partitioning changes would affect
it (sector 0 of track 1 cannot be assigned to any partition). In fact,
if you have a floppy drive, you could setup GAG on a floppy, test a
setup, and then later copy it to the MBR to eliminate having to use the
floppy. Obviously your BIOS would need to setup to boot from the floppy
first. Later, after copying GAG's multiboot manager into the HDD's MBR
bootstrap area, you configure the BIOS to boot from the drive (or just
not have a floppy in the drive so the BIOS skips it for a boot source).

http://gag.sourceforge.net/

You can find several listed at:

https://www.thefreecountry.com/utili...managers.shtml

All they do is simply change the MBR's partition table as to which
partition record is marked as the 'active' partition (which is the boot
drive). Way back there was PowerQuest with their utility that all it
did was change which partition was marked 'active' in the partition
table, you rebooted, and the other drive got used for boot. However,
that only worked for when you used multiple partitions on the same disk.
GAG will let you boot from any disk (each disk must have an MBR so it
has a partition table so a partition record can be marked 'active').

GAG has not been updated in a long time but neither has your hardware
and OS. That's what I used back when I had Windows XP and wanted to
multi-boot to different versions of Windows (GAG supports other OSes
since it is only the bootstrap loader, not the OS boot loader to which
GAG will point). Note that a multi-boot manager does not power on/off
the disks. All disks will still spin up and which is why you can select
from which one to boot its OS.

I'm assuming with Windows XP and IDE that your hardware is old which
means your motherboard uses a BIOS instead of UEFI.

wrote:
Hi,
Do to very low activity in the "Hardware" NG, I am posting the
following he

Years ago I had a conversation with a ham radio operator who
told me that he had installed two IDE HDs (Hard Drives) in his desktop PC.
Before he powered up his PC, he would flip a switch (he installed) to
select which HD will boot up. The other is "invisible" to BIOS.

Unfortunately, I had no interest in doing what he did, and I
do not have a record of his call sign since I don't keep a "Log".

Now I have a need to do the same, but I am not sure if
"switching" (by a switch) the power source (+5V, +/- 12V and
+3.3V) will "work"? In effect, the "unused" HD has it's power
cable disconnected, but the IDE data cable is still plugged
in.
Thank You in advance, John N3AOF


The ATA/ATAPI spec has "DC characteristics" as well as three appendices
of interesting info. Frequently, appendices can fill in the gaps, where
dry specsmanship does not.

http://t13.org/Documents/UploadedDoc...TA-ATAPI-6.pdf

Rudy has already hinted at the electrical issues, in his answer.

We had a succinct term for the I/O type required in your application,
at my work. We would write "this I/O needs to be fail safe on power loss".
Such a specification meant, if you lost +5V on a chip, the I/O were
not allowed to clamp the I/O bus to ground. The I/O bus was to
remain open circuit on power loss. This helps prevent stuff
from getting burned or reducing predicted device life. In modular power
situations (each subsystem has its own power supply), you have to plan
for these kinds of scenarios. What if the power goes off ? What happens ?

In a normal implementation, you put "up" and "down" clamp diodes to
the rails on the receiver. If you kill +5V, it is assumed the
upper diode pulls the I/O bus to ground, drawing excess current
from the driven end. (IBM used to put "up-up-up" "down" clamps on
their stuff, but I don't know if the intent was to reduce the
possibility of failsafe accidents or not. The three "ups" there,
refers to three diodes in series for a top-side clamp.)

On a failsafe driver, you remove the upper clamp diode. That's one
way to do it. I don't know any more details about it than that. It
was generally very hard to get full analog models from the silicon
fab (even from our own fab!), to verify behaviors like this. I got
one model from the twits in our fab, where the person doing the
extract "forgot" to put in the clamp diode model (the front end of
the pad was missing). Rendering the model file a pile of garbage.
It's even harder to work with third parties to get models (as the
model file exposes process information about their fab).

I tried using keywords such as "failsafe fail safe, hot plug, hot insert"
but cannot find any good detail for "ATA/ATAPI IDE parallel ATA" and so on.
So I cannot confirm any I/O characteristic other than the
"DC Characteristic" section of the above spec.

*******

It's easier to deny your request, for another reason.

The other issue, is signal integrity.

Host -------+---------+ OK, no bad stub for reflections
| This works better than the second config.
drive

Host -------+---------+ Still good. Design intent.
| | (Signals on this crap are never pretty!
drive drive The spec has sample 'scope-like pictures...)

Host -------+---------+ You're not supposed to do this.
| (Reflections off cable stub on end)
drive

So if you were to switch power, you'd only switch power on the
middle drive, not the end drive. And you'd still be left with the
issue of what DC effect the I/O has, caused by an unpowered drive.
Either there's the electrical load of a series damped 82 ohm resistor
on ground. Or... something.

*******

And, you can find some corny info, regarding hot swap of IDE.

http://www.overclockers.com/forums/s...rive-Enclosure

"According to the manual this enclosure will only hot-swap
in Windows 98/98SE. There is a reason you do not see IDE
hot-swap drives. The IDE interface and Windows was not
designed for it."

There is the issue of "drive detection", if you actually
powered up a drive while the OS was running. Similarly,
you'd have the issue of detecting a drive went missing.
(Does IDE offer "Safely Remove" ? I think not!).

So what the hell does Win98 have to do with this ? Puzzling...
Does Win98 assume both drives are present at all times,
and "test" before using them each time ?

*******

SATA is designed from the ground up, to support all of
this stuff. Hot insertion. It has advanced contacts on
the connector, so power/gnd pins touch before data pins.
The pin staggering only works right, in a backplane
scenario. You're on your own, in terms of connector
capture issues (tipping the connector while inserting
it, if you do it manually in your tower case). There
are some combo power+data connectors, where you'd want
to be careful of connector capture while using them.
I can't be sure the tolerance analysis was done for
that usage model. If your power and data cables
are separate, the sequence can be made a bit safer.

*******

And if you are going to try stuff like this on IDE, use
a separate I/O card. Like a VIA combo SATA/IDE
card for example. If you blow the I/O while
screwing around, it means your motherboard
remains intact. The VIA chip could be damaged,
but the damage tends not to propagate from
chip to chip on failures.

I realize hot-swap enclosures were available for IDE, but
I could never trace down any authoritative reviews
or get usage info, to prove they actually worked,
and worked without corrupting anything. Whether they
were intended for (unpowered) swapping or whatever.
The adverts always made it seem you could do anything
you want.

https://www.evertek.com/viewpart.asp?auto=2120

"Hot swappable (please see note below)

# Notes:
# Works in any OS - hot swap features only work in Windows 98/98SE
"

Usage cases to consider:

1) Normal operation. "DC Characteristics", combined with the
recommended cable config (don't do diagram #3) applies.
The stuff we rely on to work, is in the spec.

2) Remove power from chip, chip pulls to ground.
Is the IDE pad I/O failsafe ? No proof in as many words.
There is one reference in the T13 spec to providing an
"advanced ground" which implies the I/O is fail safe, but
that is pretty thin evidence indeed. If the I/O wasn't fail
safe, it would have said "advanced power/ground" instead.
Other parts of the spec show clamp diodes (naughty).

3) Hot swap/hot plug. Are dynamically added IDE devices detected?
Are dynamically removed IDE devices detected?
Does pulling a sled, corrupt actively occurring data transfers?
The existence of hot-swap enclosures clouds this issue
quite a bit, due to a lack of historical artifacts of usage.

All I can tell you, is I know what I *won't* be doing :-)

Paul

wrote:
Hi,
Do to very low activity in the "Hardware" NG, I am posting the
following he

Years ago I had a conversation with a ham radio operator who
told me that he had installed two IDE HDs (Hard Drives) in his desktop PC.
Before he powered up his PC, he would flip a switch (he installed) to
select which HD will boot up. The other is "invisible" to BIOS.

Unfortunately, I had no interest in doing what he did, and I
do not have a record of his call sign since I don't keep a "Log".

Now I have a need to do the same, but I am not sure if
"switching" (by a switch) the power source (+5V, +/- 12V and
+3.3V) will "work"? In effect, the "unused" HD has it's power
cable disconnected, but the IDE data cable is still plugged
in.
Thank You in advance, John N3AOF

We used to do this back in the PATA days with a two pole / single throw switch.
It works just fine.
Now that everything is SATA and the machines have 2 or more drives and auto
hdd recognition we unplug the power connectors from drives that we want powered off.
I suppose we could do that with SATA and a 3 pole switch but that adds complexity
and man hours to make up the looms.

On Wed, 20 Sep 2017 13:22:20 +0000, wrote:

Hi,
Do to very low activity in the "Hardware" NG, I am posting the
following he

Years ago I had a conversation with a ham radio operator who
told me that he had installed two IDE HDs (Hard Drives) in his desktop PC.
Before he powered up his PC, he would flip a switch (he installed) to
select which HD will boot up. The other is "invisible" to BIOS.

Unfortunately, I had no interest in doing what he did, and I
do not have a record of his call sign since I don't keep a "Log".

Now I have a need to do the same, but I am not sure if
"switching" (by a switch) the power source (+5V, +/- 12V and
+3.3V) will "work"? In effect, the "unused" HD has it's power
cable disconnected, but the IDE data cable is still plugged
in.
Thank You in advance, John N3AOF

I used to do that all the time. I had one drive with DOS 6.3 on it and
one with XP (W98 before that). The DPDT switch is just to select which
one is master. (and showed up as C: to boot) Because the DOS was FAT
and the XP was NTFS, XP could see both drives but DOS could only see
one.
Newer BIOSes allow selective booting so that is not necessary anymore.
You can set a prompt select which drive you want to boot. I have DOS
on a thumb stick in this machine now.

SNIP
Now I have a need to do the same, but I am not sure if
"switching" (by a switch) the power source (+5V, +/- 12V and
+3.3V) will "work"? In effect, the "unused" HD has it's power
cable disconnected, but the IDE data cable is still plugged
in.
Thank You in advance, John N3AOF

I used to do that all the time. I had one drive with DOS 6.3 on it and
one with XP (W98 before that). The DPDT switch is just to select which
one is master. (and showed up as C: to boot) Because the DOS was FAT
and the XP was NTFS, XP could see both drives but DOS could only see
one.
Newer BIOSes allow selective booting so that is not necessary anymore.
You can set a prompt select which drive you want to boot. I have DOS
on a thumb stick in this machine now.

Hi, I should have given more details why I wanted this. I want
TWO "C:" drives (one or the other is "disabled"), You can't have it that way
with a Master and Slave configured HDs unless you can switch in BIOS
settings, which one is Master and which one is Slave.

The BIOS settings in my PC has NO feature for Enabling one HD and
Disabling the other.

John

wrote:
SNIP
Now I have a need to do the same, but I am not sure if
"switching" (by a switch) the power source (+5V, +/- 12V and
+3.3V) will "work"? In effect, the "unused" HD has it's power
cable disconnected, but the IDE data cable is still plugged
in.
Thank You in advance, John N3AOF
I used to do that all the time. I had one drive with DOS 6.3 on it and
one with XP (W98 before that). The DPDT switch is just to select which
one is master. (and showed up as C: to boot) Because the DOS was FAT
and the XP was NTFS, XP could see both drives but DOS could only see
one.
Newer BIOSes allow selective booting so that is not necessary anymore.
You can set a prompt select which drive you want to boot. I have DOS
on a thumb stick in this machine now.

Hi, I should have given more details why I wanted this. I want
TWO "C:" drives (one or the other is "disabled"), You can't have it that way
with a Master and Slave configured HDs unless you can switch in BIOS
settings, which one is Master and which one is Slave.

The BIOS settings in my PC has NO feature for Enabling one HD and
Disabling the other.

John

You realize those can be added to the boot.ini on the
"BIOS-preferred" drive, right ?

The boot.ini includes an ARC path. The ARC path
has a disk number field, which means the BIOS
boots drive #1, but a reference in boot.ini can
point to drive #2.

What you need then, is for the OS to put up the
boot manager. The boot process starts with drive #1.
Then, in the menu, you see the boot choices. You
select the second one, and off it goes to drive #2.

EasyBCD makes this easy for Vista+ computers.

A text editor makes boot.ini easy for a WinXP or Win2K
computer :-) Plus or minus some attribute bits ("attrib" command)
on an NTFS partition. FAT32 partitions would make this
part easier (no permissions to worry about).

This works for relatively static situations, like
drive #1 and drive #2 are always left in the computer.
Both drives have data content storage, giving an incentive
to not remove them.

If you add drive #2 to the boot.ini on drive #1, it
doesn't prevent drive #2 from being use by itself for
boot purposes. And there's a good chance drive #1 is
not going to be checking for drive #2, when the boot.ini
is being used. Only if you actual select drive #2 in the
WinXP boot menu, and it doesn't exist, will it get upset.

I discovered the other day, that Win10 is not as happy
about that. I have two Win10 OSes on the same hard drive,
and both OSes share the same BCD file (for boot menu
purposes). If the second partition goes missing, the boot
stops and complains. Not what I was expecting. I'd
done a disk2vhd on the hard drive, and not selected
capture of the second C: partition, and the boot
process noticed and bailed on me when I tried to use
the VHD later in Virtualbox. The BCD tends to use GUID
identifiers, rather than an ARC path, and that may have
played a role in the failure.

But you should be quite safe to edit the boot.ini and
add the line to it, from the other drive. Making sure that
your ARC is actually correct.

You can probably find some examples around, of multi-boot mods.

http://best-windows.vlaurie.com/boot-ini.html

https://docs.microsoft.com/en-us/win...-boot-ini-file

With respect to "rdisk", the BIOS will probably assign
the BIOS booting drive "rdisk(0)" and consequently, the non-BIOS
boot choice you're trying to add (to the OS menu), will have
some other rdisk number, like maybe rdisk(1).

Paul

On Fri, 22 Sep 2017 10:53:03 +0000, wrote:

SNIP
Now I have a need to do the same, but I am not sure if
"switching" (by a switch) the power source (+5V, +/- 12V and
+3.3V) will "work"? In effect, the "unused" HD has it's power
cable disconnected, but the IDE data cable is still plugged
in.
Thank You in advance, John N3AOF

I used to do that all the time. I had one drive with DOS 6.3 on it and
one with XP (W98 before that). The DPDT switch is just to select which
one is master. (and showed up as C: to boot) Because the DOS was FAT
and the XP was NTFS, XP could see both drives but DOS could only see
one.
Newer BIOSes allow selective booting so that is not necessary anymore.
You can set a prompt select which drive you want to boot. I have DOS
on a thumb stick in this machine now.

Hi, I should have given more details why I wanted this. I want
TWO "C:" drives (one or the other is "disabled"), You can't have it that way
with a Master and Slave configured HDs unless you can switch in BIOS
settings, which one is Master and which one is Slave.

The BIOS settings in my PC has NO feature for Enabling one HD and
Disabling the other.

John

The master and slave is a jumper on the drive. If you replace the
jumper with a switch, you can switch master and slave by flipping the
switch. Use a DPDT and you can swap them with one switch.
You will need to power down and back up to make that work because it
determines the setting in POST.

On Fri, 22 Sep 2017 12:42:28 -0400, Paul
wrote:

wrote:
SNIP
Now I have a need to do the same, but I am not sure if
"switching" (by a switch) the power source (+5V, +/- 12V and
+3.3V) will "work"? In effect, the "unused" HD has it's power
cable disconnected, but the IDE data cable is still plugged
in.
Thank You in advance, John N3AOF
I used to do that all the time. I had one drive with DOS 6.3 on it and
one with XP (W98 before that). The DPDT switch is just to select which
one is master. (and showed up as C: to boot) Because the DOS was FAT
and the XP was NTFS, XP could see both drives but DOS could only see
one.
Newer BIOSes allow selective booting so that is not necessary anymore.
You can set a prompt select which drive you want to boot. I have DOS
on a thumb stick in this machine now.

Hi, I should have given more details why I wanted this. I want
TWO "C:" drives (one or the other is "disabled"), You can't have it that way
with a Master and Slave configured HDs unless you can switch in BIOS
settings, which one is Master and which one is Slave.

The BIOS settings in my PC has NO feature for Enabling one HD and
Disabling the other.

John

You realize those can be added to the boot.ini on the
"BIOS-preferred" drive, right ?

The boot.ini includes an ARC path. The ARC path
has a disk number field, which means the BIOS
boots drive #1, but a reference in boot.ini can
point to drive #2.

What you need then, is for the OS to put up the
boot manager. The boot process starts with drive #1.
Then, in the menu, you see the boot choices. You
select the second one, and off it goes to drive #2.

EasyBCD makes this easy for Vista+ computers.

A text editor makes boot.ini easy for a WinXP or Win2K
computer :-) Plus or minus some attribute bits ("attrib" command)
on an NTFS partition. FAT32 partitions would make this
part easier (no permissions to worry about).

This works for relatively static situations, like
drive #1 and drive #2 are always left in the computer.
Both drives have data content storage, giving an incentive
to not remove them.

If you add drive #2 to the boot.ini on drive #1, it
doesn't prevent drive #2 from being use by itself for
boot purposes. And there's a good chance drive #1 is
not going to be checking for drive #2, when the boot.ini
is being used. Only if you actual select drive #2 in the
WinXP boot menu, and it doesn't exist, will it get upset.

I discovered the other day, that Win10 is not as happy
about that. I have two Win10 OSes on the same hard drive,
and both OSes share the same BCD file (for boot menu
purposes). If the second partition goes missing, the boot
stops and complains. Not what I was expecting. I'd
done a disk2vhd on the hard drive, and not selected
capture of the second C: partition, and the boot
process noticed and bailed on me when I tried to use
the VHD later in Virtualbox. The BCD tends to use GUID
identifiers, rather than an ARC path, and that may have
played a role in the failure.

But you should be quite safe to edit the boot.ini and
add the line to it, from the other drive. Making sure that
your ARC is actually correct.

You can probably find some examples around, of multi-boot mods.

http://best-windows.vlaurie.com/boot-ini.html

https://docs.microsoft.com/en-us/win...-boot-ini-file

With respect to "rdisk", the BIOS will probably assign
the BIOS booting drive "rdisk(0)" and consequently, the non-BIOS
boot choice you're trying to add (to the OS menu), will have
some other rdisk number, like maybe rdisk(1).

Paul

A switch on the drive jumpers is easier.

SNIP
Now I have a need to do the same, but I am not sure if
"switching" (by a switch) the power source (+5V, +/- 12V and
+3.3V) will "work"? In effect, the "unused" HD has it's power
cable disconnected, but the IDE data cable is still plugged
in.
Thank You in advance, John N3AOF

I used to do that all the time. I had one drive with DOS 6.3 on it and
one with XP (W98 before that). The DPDT switch is just to select which
one is master. (and showed up as C: to boot) Because the DOS was FAT
and the XP was NTFS, XP could see both drives but DOS could only see
one.
Newer BIOSes allow selective booting so that is not necessary anymore.
You can set a prompt select which drive you want to boot. I have DOS
on a thumb stick in this machine now.

Hi, I should have given more details why I wanted this. I want
TWO "C:" drives (one or the other is "disabled"), You can't have it that way
with a Master and Slave configured HDs unless you can switch in BIOS
settings, which one is Master and which one is Slave.

The BIOS settings in my PC has NO feature for Enabling one HD and
Disabling the other.

John

The master and slave is a jumper on the drive. If you replace the
jumper with a switch, you can switch master and slave by flipping the
switch. Use a DPDT and you can swap them with one switch.
You will need to power down and back up to make that work because it
determines the setting in POST.

Hi "gfretwell",

I know about the jumper on a HD. Default is for CS (Cable Select).

Only when the PC is shut off, would I flip the switch to "swap" HDs as
Master and Slave.

Perhaps this is the method the "ham" I had a conversation with some time
ago used.

Thanks again, John

On 9/22/2017 3:53 AM, wrote:
SNIP
Now I have a need to do the same, but I am not sure if
"switching" (by a switch) the power source (+5V, +/- 12V and
+3.3V) will "work"? In effect, the "unused" HD has it's power
cable disconnected, but the IDE data cable is still plugged
in.
Thank You in advance, John N3AOF

I used to do that all the time. I had one drive with DOS 6.3 on it and
one with XP (W98 before that). The DPDT switch is just to select which
one is master. (and showed up as C: to boot) Because the DOS was FAT
and the XP was NTFS, XP could see both drives but DOS could only see
one.
Newer BIOSes allow selective booting so that is not necessary anymore.
You can set a prompt select which drive you want to boot. I have DOS
on a thumb stick in this machine now.

Hi, I should have given more details why I wanted this. I want
TWO "C:" drives (one or the other is "disabled"), You can't have it that way
with a Master and Slave configured HDs unless you can switch in BIOS
settings, which one is Master and which one is Slave.

The BIOS settings in my PC has NO feature for Enabling one HD and
Disabling the other.

John

I did a lot of experiments with dual hard drives.
Gave up after about the 10th time a linux update trashed the windows boot.
Simple solution is plugin hard drives. You can't trash a drive that's not
plugged in.
Sounds like you have IDE hard drives. Plugin drive system should be cheap.

Mike,

Plugin drive system should be cheap.

They could be. But you don't want the cheap(est) ones. I bought a number
of such disk bays and caddies (so I could multi-boot without worrying about
if the used OS would keep its fingers off of the multi-boot sofware (*coff*
MS *coff*) ), but quite soon started having lots of troubles with getting
the 'puters to start -- which instantly disappeared when I connected the
drive(s) directly to the cable.

In other words: buy a few *good* (and thus most likely more expensive) ones.

Regards,
Rudy Wieser


-- Origional message:
"mike" wrote in message
news
On 9/22/2017 3:53 AM, wrote:
SNIP
Now I have a need to do the same, but I am not sure if
"switching" (by a switch) the power source (+5V, +/- 12V and
+3.3V) will "work"? In effect, the "unused" HD has it's power
cable disconnected, but the IDE data cable is still plugged
in.
Thank You in advance, John N3AOF

I used to do that all the time. I had one drive with DOS 6.3 on it and
one with XP (W98 before that). The DPDT switch is just to select which
one is master. (and showed up as C: to boot) Because the DOS was FAT
and the XP was NTFS, XP could see both drives but DOS could only see
one.
Newer BIOSes allow selective booting so that is not necessary anymore.
You can set a prompt select which drive you want to boot. I have DOS
on a thumb stick in this machine now.

Hi, I should have given more details why I wanted this. I want
TWO "C:" drives (one or the other is "disabled"), You can't have it
that way
with a Master and Slave configured HDs unless you can switch in BIOS
settings, which one is Master and which one is Slave.

The BIOS settings in my PC has NO feature for Enabling one HD and
Disabling the other.

John

I did a lot of experiments with dual hard drives.
Gave up after about the 10th time a linux update trashed the windows boot.
Simple solution is plugin hard drives. You can't trash a drive that's not
plugged in.
Sounds like you have IDE hard drives. Plugin drive system should be
cheap.