Azure Confidential Ledger, like the Azure Blockchain Service, builds on the idea that blockchain is a distributed ledger. Microsoft's Azure Confidential Ledger (ACL) adds an extra layer of security and scalability on top of blockchain. ACL uses the Azure Confidential Computing Platform, meaning an instance of ACL runs in a dedicated and fully attested hardware-backed enclave.
ACL is built on top of the Confidential Consortium Framework (CCF), which Microsoft officials showed off publicly in 2017. At that time, officials said the Coco (short for "confidential consortium") Framework was meant to work with any ledger protocol and work on any operating system and hypervisor that supports a compatible Trusted Execution Environment (TEE), or secure area of a processor. The Framework was designed to be used on-premises and/or in various vendors' clouds, officials said.
Microsoft officials said ACL works well when users need audit logging and tracking of highly sensitive admin operations. They suggested that healthcare, financial and retail, information technology, supply chain monitoring and any business where contracts and deeds need to be exchanged securely would all be good candidates for ACL.
I asked Microsoft if ACL should be considered the replacement for Azure Blockchain as a Service and got no direct reply. Instead, a spokesperson said "We are asking (Azure Blockchain Service) customers to transition to the ConsenSys Quorum Blockchain Solution. As industry dynamics have changed, we made the decision to shift our focus from a product-oriented offering to a partner-oriented solution."
Update (May 25). And here's the direct reply on positioning of ACL, courtesy of a spokesperson:
"Azure Confidential Ledger doesn't replace Azure Blockchain Service but is another distributed ledger that can be used by customers who want the maximum level of privacy afforded to them. With Azure Confidential Ledger, customers can take advantage of Azure's Confidential Computing to harness the power of secure enclaves when setting up the distributed blockchain network. In comparison, ConsenSys Quorum Blockchain Service is built on ConsenSys Quorum, an open source technology that is fully compatible with Azure Blockchain Service and will provide a seamless migration experience for users."