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The IBM System/370 (S/370) was a model range of IBM mainframe computers announced on June 30, 1970 as the successors to the System/360 family. The series mostly〔E.g., programs that depended on getting program interrupts for alignment errors might fail.〕 maintained backward compatibility with the S/360, allowing an easy migration path for customers; this, plus improved performance, were the dominant themes of the product announcement. Improvements over the S/360 first released in the S/370 model range included: * The block multiplexor channels introduced on the most recent high end System/360 systems. * standard dual-processor capability; * "monolithic main memory" on the model 145, based on integrated circuits instead of magnetic cores; However, the larger models 155 and 165 still used core memory. * full virtual memory through a new microcode floppy disk on the 370/145 and a hardware upgrade to include a DAT box on the 370/155 and 370/165; these were not announced until 1972; * 128-bit (hexadecimal) floating point arithmetic on all models.〔The 360/85 had extended precison floating point.〕 ==Evolution== The original System/370 line underwent several architectural improvements during its roughly 20-year lifetime. One very significant change was the introduction of virtual memory, which was first made generally available in 1972 via IBM's "System/370 Advanced Function" announcement. IBM had initially (and controversially) chosen to exclude virtual storage from the S/370 line. The August 2, 1972 announcement included: * Address relocation hardware on all S/370s except the original models 155 and 165 * The new S/370-158 and -168 * Four new operating systems: DOS/VS (DOS with virtual storage), OS/VS1 (OS/360 MFT with virtual storage), OS/VS2 (OS/360 MVT with virtual storage) Release 1, termed SVS (Single Virtual Storage), and Release 2, termed MVS (Multiple Virtual Storage) and planned to be available 20 months later (at the end of March 1974), and VM/370 – the re-implemented CP/CMS Virtual memory had in fact been delivered on S/370 hardware before this announcement: * In June 1971, on the S/370-145 (one of which had to be “smuggled” into Cambridge Scientific Center to prevent anybody noticing the arrival of an S/370 at that hotbed of virtual memory development – since this would have signaled that the S/370 was about to receive address relocation technology). (Varian 1997:p29〔) The S/370-145 had an associative memory〔 used by the microcode for the DOS compatibility feature from its first shipments in June 1971; the same hardware was used by the microcode for DAT. Although IBM famously chose to exclude virtual memory from the S/370 announcement, that decision was being reconsidered during the completion of the 145 engineering, partly because of virtual memory experience at CSC and elsewhere. The 145 microcode architecture simplified the addition of virtual memory, allowing this capability to be present in early 145s without the extensive hardware modifications needed in other models. However, IBM did not document the 145's virtual memory capability, nor annotate the relevant bits in the control registers and PSW that were displayed on the operator control panel when selected using the roller switches. The Reference and Change bits of the Storage-protection Keys, however, were labeled on the rollers, a dead giveaway to anyone who had worked with the earlier 360/67. Existing S/370-145 customers were happy to learn that they did not have to purchase a hardware upgrade in order to run DOS/VS or OS/VS1 (or OS/VS2 Release 1 – which was possible, but not common because of the limited amount of main storage available on the S/370-145). Shortly after the August 2, 1972 announcement, DAT box (address relocation hardware) upgrades for the S/370-155 and S/370-165 were quietly announced, but were available only for purchase by customers who already owned a Model 155 or 165. After installation, these models were known as the S/370-155-II and S/370-165-II. IBM wanted customers to upgrade their 155 and 165 systems to the widely-sold S/370-158 and -168.〔 – tables include model characteristics (Table 1) and announcement/shipment dates (Table 2). The S/370-155-II and -165-II are listed under the former but not the latter, because the upgraded systems were not formally announced as separate models. The "System/370 Advanced Function" announcement, including the -158 and -168, was the main public event.〕 These upgrades were surprisingly expensive ($200,000 and $400,000, respectively) and had long ship date lead times after being ordered by a customer; consequently, they were never popular with customers, the majority of whom leased their systems via a third-party leasing company. This led to the original S/370-155 and S/370-165 models being described as "boat anchors". The upgrade, required to run OS/VS1 or OS/VS2, was not cost effective for most customers by the time IBM could actually deliver and install it, so many customers were stuck with these machines running MVT until their lease ended. It was not unusual for this to be another four, five or even six years for the more unfortunate ones, and turned out to be a significant factor in the slow adoption of OS/VS2 MVS, not only by customers in general, but for many internal IBM sites as well. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「IBM System/370」の詳細全文を読む スポンサード リンク
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