You will not be able to install Rockstor on ReadyNAS 1100 because the ReadyNAS 1100 is not Intel/AMD. ReadyNAS 1100 runs on SPARC processor, which is old school and probably not supported by Rockstor.
Rockstor theoretically can be installed on some Netgear’s Intel/AMD devices. Look for the ones that come with USB drives inside the chassis as the boot drive. These include the Big RN32xx, RN 33xx and RN 42xx, 43xx and ReadyNAS Pros, and ReadyNAS 3xx, 4xx, 5xx, 6xx… and a few others
ReadyNAS 1xx and 2xx and 2120 will not not work as it runs ARM (which is probably also not supported by Rockstor)
Rockstor will definitely not work on any Netgear SPARC ReadyNAS
From this site you can see what each model of NAS is running as chipset: https://kb.netgear.com/20684/ReadyNAS-Downloads
Downloads for latest ReadyNAS OS 6 devices:
(1)*arm (Version 6.8.1) for RN102 / RN104 / RN202 / RN204 / RN212 / RN214 / RN2120
(2)*x86_64 (Version 6.8.1) for RN312 / RN314 / RN316 / RN422 / RN424 / RN426 / RN428 / RN516 / RN524X / RN526X / RN528X / RN626X / RN628X / RN716X / RR2304 / RR2312 / RN3130 / RN3138 / RN3220 / RR3312 / RN4220 / RR4312X / RR4312S / RR4360X / RR4360S
Downloads for previous ReadyNAS devices:
(3)*RAIDiator 5.3 (version 5.3.12) for DuoV2 / NV+V2
(4)*RAIDiator 4.2 (version 4.2.30) for Pro Pioneer / Pro Business / Pro 2 / Pro 4 / Pro 6 / NVX / Ultra 2 / Ultra 4 / Ultra 6 / Ultra 2 Plus / Ultra 4 Plus / Ultra 6 Plus / 1500 / 2100 / 3100 / 3200 / 4200
(5)*RAIDiator 4.1 (version 4.1.15) for Duo / NV+ / 1100 <-- your 1100 is way too old, its running Sparc
You won’t be able to run it on 1,3 and 5 as they are ARM or SPARC.
You theoretically can run on 2 and 4, as long as they use a USB boot drive. If the boot drive is a chip then good luck (it still might be possible). Note to get to the BIOS on some of these devices you need special cable that netgear can get easily (not sure if they share it with random people). You might not need to get to the BIOS after all.