No , an Embedded PC is also an embedded system . But as you post this here I can makeout you mean regarding 8bit system. Actually a middle ware is a kinda program simplification scheme in multiprocessor system ,where plenty of microcontrollers are interacting with each other and sharing a common data bus , middle ware can be event based to allow distributed control and efficient exploitation of the resource. Middleware has different menings in different systems , some where it can be used as a filter software somewhere it can be used as a management software .Thus it may improves the modularity and efficiency of system by distributing some software tasks to other microcontrollers and communicating only the relevant data to the main processor.
So you can think middleware is a term for any programming that can exchange or mediate between two different programs , to effectively exploite its resourse. It provide a type of data exchange between the too and enable different applications to communicate .One can say a DDE in between various VC++ applications an EXCEL and VB applications (exe files) of the same kind in a higher level system .

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AP