Installation of Solaris 7 on an Enterprise 420r "either from 
cdrom or JumpStart"(Part 704-6333-11 October 1998 Revision A) 
may fail with "cannot open kernel/unix" on initial boot as shown below:

ok boot cdrom
Resetting ... 

Sun Enterprise 420R (4 X UltraSPARC-II 450MHz), No Keyboard
OpenBoot 3.23, 4096 MB memory installed, Serial #11283083.
Ethernet address 8:0:20:ac:2a:8b, Host ID: 80ac2a8b.

Rebooting with command: boot cdrom                                    
Boot device: /pci@1f,4000/scsi@3/disk@6,0:f  File and args: 
boot: cannot open kernel/unix
Enter filename [kernel/unix]:                   

The first release of Solaris 7 (FCS) is not supported on the Enterprise 420r.
Solaris 7 HW 8/99 and 11/99 are the only "hardware" versions of 
Solaris 7 supported on the E420r.  

The following HW versions of Solaris 7 are also NOT supported on the 420r:

**Solaris 7 HW 3/99 (Part 704-6521-10 March 1999, Revision A) 
**Solaris 7 HW 5/99 (Part 704-6660-10 May 1999, Revision A)


ADDITIONAL NOTES:                   

Solaris 2.5.1 HW 11/97 is supported on the Enterprise 420R.

Solaris 2.6 HW 5/98 is supported on the Enterprise 420R.  When 
installing this version of Solaris, you will need to boot to 
the Operating Environment CD first and follow the instructions displayed on 
the console thereafter.