according to the definition found in this website composable architecture is:
https://www.hpe.com/us/en/what-is/composable-infrastructure.html
In composable infrastructure, compute, storage, and networking resources are abstracted
from their physical locations,and can be managed by software, through a web-based interface.
Composable infrastructure makes data center resources as readily available as cloud services, and is the foundation for private and hybrid cloud
solutions.
what is the difference between composable architecture and Platform as a Service such as AWS services?
can I say if Im running in AWS that I have a composable architecture?
First of all, composable infrastructure is an infrastructure; not a platform and therefore its comparison with PaaS is not correct. The comparison should be with IaaS, not PaaS.
The most basic difference between a composable infrastructure and IaaS is that in case of composable infrastructure, it's you who manage everything (in your own datacentre) while in case of IaaS, a part of the infrastructure management goes to the hands of IaaS provider. You can check https://www.bmc.com/blogs/saas-vs-paas-vs-iaas-whats-the-difference-and-how-to-choose/ to understand what you manage and what the cloud providers manage.
Composable infrastructure is a way to get the flexibility of IaaS using the virtualization management tools and technologies like Chef, Puppet and Docker in your existing datacentre. You can check https://techbeacon.com/enterprise-it/5-things-you-need-know-about-composable-infrastructure for more information.