define: Physical vs Logical vs Virtual

In network and computer systems management there are many "abstractions" and it is useful to have a clear terminology. Definitions / meaning vary depending on context; here is one approximation:

• Physical devices: actual device being monitored or managed
• Logical devices: abstracting one or more physical devices to expose simpler or extended properties or functionality 
• Virtual devices: abstracting resources to make it more accessible and manageable; Virtual devices have appearance of physical devices, but actual implementation could be different, sometimes using Logical devices.  

logical vs. physical Definition from PC Magazine Encyclopedia
"High-level versus low-level. Logical implies a higher view than the physical. Users relate to data logically by data element name; however, the actual fields of data are physically located in sectors on a disk."

"Various virtualization methods create a logical "abstraction layer" for dealing with the physical hardware. For example, virtual machines enable multiple operating systems to run in the computer, each accessing the hardware via a logic layer rather than direct physical contact."
logical vs. physical topology Definition from PC Magazine Encyclopedia
"A logical topology is how devices appear connected to the user. A physical topology is how they are actually interconnected with wires and cables."

Re: [vnrg] Logical vs. virtual @ IETF
"a virtual resource appears to a user of that resource as if he is the (exclusive) owner of that resource. A user's access is always carried out on the real resource. Thus, a virtual resource simplifies the handling of a scarce real resource, while hiding the shortage. Virtual memory is a typical example here - a process can use a larger virtual memory than there is physically real memory available."

Difference between logical interface and virtual interface - The Cisco Learning Network
"Anything that does not have a "physical" presence is technically a "logical" interface. So therefore virtual interfaces ARE logical interfaces."

Understanding Virtual and Logical processors | Hyper-V content from Windows IT Pro
"virtual machines (VMs) are given a certain number of virtual processors, which use up resources on actual processor cores on the server (logical processors)."

linux kernel - Difference between physical/logical/virtual memory address - Stack Overflow
"Virtual address: The address you use in your programs, the address that your CPU use to fetch data, is not real and gets translated via MMU to some physical address; everyone has one and its size depends on your system(Linux running 32-bit has 4GB address space)
Physical address:
The address you'll never reach if you're running on top of an OS; it's where your data, regardless of its virtual address, resides in RAM; this will change if your data is sent back and forth to the harddisk to accommodate more space for other processes."

what differences and relations are between logical and virtual memory? - Super User

"logical address" means that the address the program sees is different from the physical address of the data being stored in RAM.
If you have virtual memory, there may be no physical address at all, as the data stored could be swapped out to disk."

Logical partition (virtual computing platform) - Wikipedia, the free encyclopedia
"A logical partition... is a subset of computer's hardware resources, virtualized as a separate computer. In effect, a physical machine can be partitioned into multiple logical partitions, each hosting a separate operating system."