This image shows the Boot volume portion of the Create compute instance, Storage page.

There is text "A boot volume (this is a link) is a detachable device that contains the image used to boot the compute instance."

There are options:

--Specify a custom boot volume size (selected and surrounded by a red border)
The text below the check box reads "Volume performance (this is a link) varies with volume size. Default boot volume size: 75 GB. When you specify a custom boot volume size, service limits apply." 

--Boot volume size (GB) field showing sample text.

--Boot volume performance field
--IOPS
--Throughput
--Target volume performance

There is text "Balanced choice for most workloads including those that perform random I/O such as boot disks. Actual performance depends on the attached instance's shape. Select the appropriate instance shape to optimize performance. Balanced performance can have IOPS of 60 IOPS/GB up to a maximum of 25000 IOPS and throughput of 480 KB/s/GB up to a maximum of 480 MB/s. Learn more (this is a link.)"   

--Use in-transit encryption (switch, selected)
The text below the check box reads "Encrypts data (link) in transit between the instance, the boot volume, and the block volumes."

--Encrypt this volume with a key that you manage (switch, not selected)
The text below the check box reads "By default, Oracle manages the keys that encrypt this volume, but you can choose a key from a vault that you have access to if you want greater control over the key's lifecycle and how it's used. How do I manage my own encryption keys? (this is a link)."