Dos requires drivers for the cd-rom to become visible.

Win95/98 startup disk loads cd-rom drivers at boot.

Your Win95 cd is probably/certainly not bootable. That has nothing to do with the OS already on the machine, that has to do with the disk itself, and whether your hardware supports booting from cd (probably not).
You need a boot disk with cd support, I don't know what kind of boot disk you're using - if it's the one that came with your Windows CD I would assume it's got cd-rom support...
I suggest you download a Win98 boot disk that includes cd rom support and use WinImage to write that to floppy.
Assuming you're using an IDE cd-rom drive, if you're using one with an older interface you need the right drivers for that.

An easier workaround, though, is to use your current Windows installation to copy the contents of your OSR2 cd to somewhere on your hard drive.
Then restart into DOS mode and run the installer from that location.

Oetker wrote on 2021-03-12, 10:42:

An easier workaround, though, is to use your current Windows installation to copy the contents of your OSR2 cd to somewhere on your hard drive.
Then restart into DOS mode and run the installer from that location.

I think the same. Win 9x Setup has that bad habbit of forgetting to integrate a CD-ROM driver early on in the installation process.
Not seldomly, after first reboot, it will be unable to access the setup files stored on the CD-ROM drive.
Which is silly, because among these files are CD-ROM drivers, too. 🤦
The root cause of this issue is, that the initial 9x setup was usually started with the help of DOS-based CD-ROM drivers (stored on start-up floopy), which Win9x tries avoid using at all costs (it prefers native Win9x drivers).

Oetker wrote on 2021-03-12, 10:42:

An easier workaround, though, is to use your current Windows installation to copy the contents of your OSR2 cd to somewhere on your hard drive.
Then restart into DOS mode and run the installer from that location.

Just gave this a shot, ended with the same result:

Warning SU0168

Your computer already has an operating system installed, which cannot be upgraded by this version of Setup. Please obtain the Windows 95 Upgrade.

Giving it another shot with a 98 bootdisk.

Jo22 wrote on 2021-03-12, 11:09:

I think the same. Win 9x Setup has that bad habbit of forgetting to integrate a CD-ROM driver early on in the installation proce […]
Show full quote

Oetker wrote on 2021-03-12, 10:42:

An easier workaround, though, is to use your current Windows installation to copy the contents of your OSR2 cd to somewhere on your hard drive.
Then restart into DOS mode and run the installer from that location.

I think the same. Win 9x Setup has that bad habbit of forgetting to integrate a CD-ROM driver early on in the installation process.
Not seldomly, after first reboot, it will be unable to access the setup files stored on the CD-ROM drive.
Which is silly, because among these files are CD-ROM drivers, too. 🤦
The root cause of this issue is, that the initial 9x setup was usually started with the help of DOS-based CD-ROM drivers (stored on start-up floopy), which Win9x tries avoid using at all costs (it prefers native Win9x drivers).

I had installed the dos drivers for the CD drive, but to no avail. It still says "Invalid drive specification"

Asches wrote on 2021-03-13, 08:35:

Just gave this a shot, ended with the same result: […]
Show full quote

Oetker wrote on 2021-03-12, 10:42:

An easier workaround, though, is to use your current Windows installation to copy the contents of your OSR2 cd to somewhere on your hard drive.
Then restart into DOS mode and run the installer from that location.

Just gave this a shot, ended with the same result:

Warning SU0168

Your computer already has an operating system installed, which cannot be upgraded by this version of Setup. Please obtain the Windows 95 Upgrade.

Giving it another shot with a 98 bootdisk.

Some googling tells me that deleting some files from your current Windows install should fix the issue. I would just restart into DOS mode and deltree c:\windows.

Asches wrote on 2021-03-13, 08:37:

Jo22 wrote on 2021-03-12, 11:09:

I think the same. Win 9x Setup has that bad habbit of forgetting to integrate a CD-ROM driver early on in the installation proce […]
Show full quote

Oetker wrote on 2021-03-12, 10:42:

An easier workaround, though, is to use your current Windows installation to copy the contents of your OSR2 cd to somewhere on your hard drive.
Then restart into DOS mode and run the installer from that location.

I think the same. Win 9x Setup has that bad habbit of forgetting to integrate a CD-ROM driver early on in the installation process.
Not seldomly, after first reboot, it will be unable to access the setup files stored on the CD-ROM drive.
Which is silly, because among these files are CD-ROM drivers, too. 🤦
The root cause of this issue is, that the initial 9x setup was usually started with the help of DOS-based CD-ROM drivers (stored on start-up floopy), which Win9x tries avoid using at all costs (it prefers native Win9x drivers).

I had installed the dos drivers for the CD drive, but to no avail. It still says "Invalid drive specification"

Hi again! I'm not sure if you do understand what I meant to say. Maybe it's because of my poor English, not sure (I'm no native speaker sadly). 😅

What I meant to say: I remember my father's old 386 PC..

It had an early generation Mitsumi single-speed CD-ROM drive with a proprietary (by todays standard) interface card.. :

It required a special CD-ROM driver for DOS which he had installed, too.

During the upgrade process from Win3.1/DOS6.20 to Windows 95, the Win95 setup did remove it from config.sys.
Win95 setup also did remove MSCDEX from autoxec.bat.

After first reboot, the previously installed CD-ROM drivers for MS-DOS were gone.
Win95 setup thus nolonger was able to access the CD-ROM drive.

So my father had to manually had to edit them and put the entries for these back into them.

After this, Win95 setup was able to continue.

This was before we had big HDDs.

At the time, Win95 weighted about a hefty 40MB (!), so copying setup files to HDD was no viable option.

Asches wrote on 2021-03-13, 08:37:

Jo22 wrote on 2021-03-12, 11:09:

I think the same. Win 9x Setup has that bad habbit of forgetting to integrate a CD-ROM driver early on in the installation proce […]
Show full quote

Oetker wrote on 2021-03-12, 10:42:

An easier workaround, though, is to use your current Windows installation to copy the contents of your OSR2 cd to somewhere on your hard drive.
Then restart into DOS mode and run the installer from that location.

I think the same. Win 9x Setup has that bad habbit of forgetting to integrate a CD-ROM driver early on in the installation process.
Not seldomly, after first reboot, it will be unable to access the setup files stored on the CD-ROM drive.
Which is silly, because among these files are CD-ROM drivers, too. 🤦
The root cause of this issue is, that the initial 9x setup was usually started with the help of DOS-based CD-ROM drivers (stored on start-up floopy), which Win9x tries avoid using at all costs (it prefers native Win9x drivers).

I had installed the dos drivers for the CD drive, but to no avail. It still says "Invalid drive specification"

Although I would still recommend installing from HD, the poster above is right, you might not have a compatible CD-ROM drive, although I would expect to see that on an older machine. Does the boot disk say anything about its initialization of the CD drivers during startup?

The conventional CD-ROM interface we're all familiar with was only standardized in the late-1990s, when ATAPI became a thing. Before then CD interfaces were proprietary and mutually incompatible. Getting them all to work in MS-DOS was already a headache. You needed a special driver from the manufacturer (not OAKCDROM.SYS).

Invalid drive specification means the driver loaded, couldn't find the drive and aborted.

What is the model of the CD drive? that'll confirm what driver you want to use.
And just to be sure Where is the CD plugged in? IDE1, IDE2, SCSI, or off the back of the sound card?

If you have another PC with a floppy drive you can download the original Win95 boot disk from here.
https://www.allbootdisks.com/download/95.html
This does an OK-ish job at autodetecting IDE drives. but wont help with SCSI or if using the sound card.

Once we get D drive been recognised we can worry about actually installing windows

Windows 95 and "Woes" is an oxymoron.