From mboxrd@z Thu Jan 1 00:00:00 1970 From: paul.winalski@gmail.com (Paul Winalski) Date: Mon, 30 Apr 2018 12:43:50 -0400 Subject: [TUHS] /dev/drum In-Reply-To: <20180430150532.4B67218C09C@mercury.lcs.mit.edu> References: <20180430150532.4B67218C09C@mercury.lcs.mit.edu> Message-ID: On 4/30/18, Noel Chiappa wrote: > > There's also the System 360 approach, where processes share a single > address > space (physical memory - no virtual memory on them!), but it uses > protection > keys on memory 'chunks' (not sure of the correct IBM term) to ensure that > one > process can't tromp on another's memory. IBM always used the term "storage" rather than "memory". The Storage Protection feature for System/360 was optional on some models, and provided a 4-bit protection key for each 2048-byte block (IBM's term) of physical storage, allowing for up to 15 processes to be executing simultaneously (key value 0 disabled storage protection). The System/370 operating systems DOS/VS, OS/VS1, and OS/VS2 SVS all had a single, demand-paged virtual address space, usually a few times larger than the physical memory. For DOS/VS the virtual address space was partitioned into a space (mapped virtual=physical address) starting at address 0 for the OS, then up to five user program partitions. Programs were linked to run in one of these partitions. OS/VS1 (successor to OS/360 MFT) also had a single virtual address space, but it had more partitions and the program loader could dynamically relocate applications to run in any of the partitions. OS/VS2 SVS (first successor to OS/360 MVT) had a single virtual address space, but dynamically allocated partitions as needed. OS/VS2 MVS had processes in the modern OS sense--each executing program got its own virtual address space. -Paul W.