I mentioned this in my post about DR-DOS.
PC DOS 7.1 is often confused with 7.01, also known as PC DOS 2000. PC DOS 7.01 is a modest bug-fix for MS-DOS 6.22, but with a bunch of Microsoft tools removed and replaced with IBM equivalents – so it has IBM's E editor instead of EDIT.EXE, Rexx instead of QBASIC, IBM antivirus and so on.
PC DOS version 7.1 is a different beast. It's based off the same core as the embedded DOS in Windows 95B (OSR2) and Windows 98. It supports FAT32, including the ability to boot from them. It supports LBA hard disks, meaning it can handle volumes of over 8GB. It fixes a lot of bugs in the DOS codebase.
Here's some more information (in Spanish but Google translates it fine.)
The primary author, Vernon Brooks, has a site which details the development history and itemises his fixes.
Here is how to get PC DOS 7.1, which IBM makes available as a free download. You may have to hunt -- the ServerGuide toolkit is quite old now.
Here is at least one method to install it in VirtualBox.
Note, PC DOS 7.1 is not a complete OS. Unfortunately, in this way it resembles DR's versions of DR-DOS 7.04 and later, which consists only of boot files embedded into the startup diskettes for products such as Seagate Disk Manager and Powerquest PartitionMagic. For 7.1, IBM only updated the kernel and some core tools.
To make a complete OS from this, you need a full copy of PC DOS 2000, then replace some of its files with the updated ones from the SGTK, as detailed above. I am reluctant to link to sources for this, as it is still copyright code. If you can't find it, ask me.
I have done this and can confirm that it works and works well. I have it running inside VirtualBox, and booting natively on the bare metal of a Lenovo Thinkpad X200. It is somehow aesthetically pleasing to have IBM PC DOS running natively on modern hardware that still has IBM branding. I can also say that classic DOS word-processors such as MS Word 6 and WordPerfect 6 run both very well and very quickly on it.