how to install windows 98 alongside Windows 10?

no vmware,just alongside Windows 10

There are a variety of reasons why that would be difficult to almost impossible. A big one being device drivers. Any computer that supports Windows 10 would likely not have drivers available for Windows 98.

Using a virtual machine is going to be MUCH easier.

I think you will have to use legacy boot mode. I don't think Windows 98 supports EFI booting.

This is exactly the reason virtualization became the way to go as opposed to trying to get a decades old OS shoehorned onto a modern PC.

I'm curious as to why you wouldn't want to virtualize.

Windows 98 is so limited that it will crash if system RAM is more than 1 GB.

https://support.microsoft.com/en-us/kb/304943

With many workarounds and third party patches like How To Install USB Mass Storage Device on Windows 98 • Raymond.CC, you may be able to make Win98 up and running on a modern PC. However i would recommend buying an old refurbished Pentium 4 machine which has out of box support for legacy OS like Win98.

That's another benefit of virtualization...you can limit the amount of memory available to the system. You could easily run a VM with 512 MB of memory.

Win 98/ 98SE only works on a FAT32 filesystem and as stated the ram limitations, ACHI, drivers and compatibility for newer hardware let alone Antivirus and firewall compatibility.
I take it you ask due to the possibility of trying out: this
As per previous VM is the way to go with that, or an old PC/ laptop

Tried this a few years ago and all worked with 256mb Ram but, was too apprehensive to connect to the internet as I could not find an antivirus/ firewall.