Distributed Operating Systems

DOS's attempt to provide the abstraction of a centralised time-sharing system to users. This is achieved using multiple processors conencted to a network. Details such as the location of files, the network type and processor being used are hidden from the user by the DOS.


V operating system

The V operating system (sometimes V-System) is a microkernel distributed OS which controls a cluster of high-performance workstations on a high-speed network. It provides network-transparent address spaces, light-weight processes, and IPC using blocking-RPC.
Processes, process groups and communication endpoints are identified by unique 64-bit numbers called entity identifiers. These are host-independent. The kernels cooperate in the allocation of entity ID's to ensure that they are unique on a network-wide basis.
V inter-process communication is request-response based. Messages are of a fixed length of 32-bytes, with an optional attached data segment of up to 32-kbytes.
Multicast is used for dissemination of load information and for synchronisation of theV time servers. Processes may be collected into groups. Group IDs are taken from the same name space as process IDs.
Physical memory in V is organised as a cache of pages from open files. Each process address space is organised as a set of address ranges called regions. Each region is bound to a portion of an open file, providing the process with a window onto that portion of the file.
The kernel manages binding, block caching and consistency. Consistency is achieved using locking at the file server and a block-owndership protocol.
A V object is a process, an address space, a communications port or an open file. All servers are effectively object managers. The manager of an object is found by multicasting the character-string object name to the name handling group.


Amoeba

Amoeba is a distributed OS consisting of a (distributed) kernel and a suite of services.
Services are accessed using RPC and the OS Controls workstations, pool processors, specialised servers and gateways.
Amoeba is object based where an object is defined as a piece of data on which well-defined operations can be performed by authorised users.
Objects are accessed and protected by unique object capabilities, which form a 128-bit wide name space. Capabilities are protected from illegal modification by the inclusion of redundancy and a checksum field.
The bullet service provides file access. In Amoeba, files are immutable and contiguous (both on disk and in file server cache).
Amoeba processes may be either running or stunned. Stunning is used for program debugging and process migration.

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