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diff --git a/overview.rst b/overview.rst index e3a60e8..483bea5 100644 --- a/overview.rst +++ b/overview.rst @@ -2,33 +2,34 @@ Overview -------- EUMEL is different from conventional operating systems in a lot of ways. Some -of them were neccessary due to hardware constraints at that time and others +of them were neccessary due to hardware constraints at the time and others were deliberatly designed this way. EUMEL’s key features are: Hardware independence The OS has *two* hardware abstraction layers, significantly improving its - portability. The first one, Software/Hardware (SHard), provides functions - for a concrete machine, such as the Olivietti M20, Amiga ST or IBM PC - AT/XT. EUMEL0 (Urlader), the second layer, implements a virtual machine on + portability. The first one, Software/Hardware (SHard), provides functions + for a concrete machine, such as the Olivetti M20, Amiga ST or IBM PC + AT/XT. EUMEL0 (Urlader), the second layer, implements a virtual machine on top of a specific processor architecture like Z80 or x86. Programs are - compiled into bytecode for this machine and thus independent of the actual - machine they are running on. + compiled into bytecode for the virtual EUMEL0 machine, making them portable + across different machines. Single-level store - Every object (dataspace) lives in a single, virtual address space. The - memory is organized into pages, which can reside in memory or on disk. - The operating system transparently moves pages to disk if they have not - been in use lately and reads them back as soon as a process requests it - ([praxis2]_, p. 82). + Every object (dataspace) lives in a single, virtual address space. A + dataspace is divided into pages, which can reside in memory or on disk. + The operating system transparently moves (swaps) pages to disk if they have + not been in use lately and reads them back as soon as a process needs the + data. Every file and every task is a dataspace. Copy on write - Pages are shareable and EUMEL automatically unshares them if one copy is - written to. + Pages are shareable and can be copied without a cost. EUMEL automatically + unshares them if changes are made to one of the copies. Persistence - Every file and every task is a dataspace. Since they all reside in the - single-level store the machine can powered off and back on again, with all - tasks starting from the point where they left off. -Time-sharing and multi-user + Since everything resides in the single-level store the machine can powered + off and back on again, with all tasks restarting execution from the last + snapshot. These are created on request and every 15 minutes. +Time-sharing, multi-user and network-transparency A single machine running EUMEL is capable of serving multiple “thin - clients” connected via serial lines. + clients” connected via serial lines. Additionally users can share files and + start remote processes by linking multiple machines with *EUMEL-Netz*. One-language concept *ELAN (Elementary Language)* is system implementation language, programming language, shell language and documentation language. |