CDC 6600 - Why so awesome?

On 06/22/2016 08:32 AM, Swift Griggs wrote: I think Paul's covered that pretty well. I'll add that the more complex the display, the more flicker was present. Another odd effect was that systems that made extensive use of ECS (extended core storage) could make the display flicker something awful, as ECS transfers tended to be block-oriented, due to the high startup time. (ECS used a wide word that was disassembled into CM words. Once a transfer started, it was at full central memory speed.) ECS transfers could also torpedo certain types of tape I/O (e.g. 1LT, the long tape driver used to transfer records longer than PP memory to CM). Do check it out--there was some bleeding-edge technology that went into that system that was later used by Cray in his 6600. One of those project that could be said to be a technical success, but a financial fiasco. Well, SCOPE had INTERCOM, an interactive facility, as well as EXPORT/IMPORT which was an RJE facility. But the system was targeted primarily at batch jobs. Its illegitimate relative, KRONOS, made extensive use of ECS for support of the PLATO system. Note that the 6000 series had no hardware memory management to speak of. An active job had a relocation address (RA) and field length (FL), but memory space belonging to a job was contiguous and present in physical memory (no paging or segmentation). So jobs were moved or "rolled out" to mass storage as needs for resources arose. So that was for standard offerings--"special systems" (i.e. spooks) had their own adaptations, probably still classified today. However, there was more than one SCOPE--and when reading the bitsavers stuff, you have to be careful. The CDC 7600 used pretty much the same CPU instruction set as the 6000 series, so user programs were compatible. The PP setup was different however. In the 6000, any PP has unrestricted access to central memory (CM). In the 7600, each PP was assigned a fixed memory frame in CM and could not access anything outside of its hard-wired "buffer" area. The implication is that you couldn't have a PP-resident operating system. So SCOPE 2 was developed for the 7600. In it, PPs are relegated to I/O and (one very special unit) for maintenance. The operating system proper resides in a set of "nested" program units. That is, there would, for example be a Buffer Manager with an RA and FL that encompassed the Record Manager program, which, in turn would encompass the Job Supervisor...and eventually the user program itself. A system of "rings of protection" if you will, long before that was in vogue. Although bulk core (LCM = large core memory; the 7600 term for 6000 ECS) was used as program storage, the whole affair turned out to be more cumbersome than originally envisioned. The SCOPE 2 folks were always a little defensive about this result of necessity. So, SCOPE 2 is not the same as SCOPE 3. SCOPE 3.4 was the last version to be called that before it was renamed NOS/BE (Network Operating System, Batch Environment) and eventually merged into NOS proper (which had been KRONOS, which had been NOS). CDC was sharply split in culture as well as geography--the Minnesota clan was cut from different cloth than the Palo Alto-then-Sunnyvale clan, so discussions from the West coast tend to be more SCOPE-oriented, while the pickled watermelon rind clan talks fondly about KRONOS. Working with full words and shifting and masking can be remarkably efficient. For a time, CDC had one of the fastest COBOLs around, even against IBM's big iron. I recall the "what do we do about more than 64 characters" discussion was raging. One interesting alternative proposed was to fit 7.5 8-bit characters to the word, with the odd 4-bit leftover being called a "snaque" (snaque-byte; get it?). Instead what was done was to reserve some of the lesser used characters of the 64-character set as "escape" codes for what amounts to 12-bit characters. So, in theory, you get the advantage of uppercase compatability, while providing for an extended character set. Very messy. As an aside, take a look at the UNIVAC 1107/1108 instruction set from roughly the same period. It has an instruction to define the byte size (36 bit words). Another cultural difference. CDC had coding standards. When a programmer wrote code that either defined a new product or modified an existing one, it had to pass peer review. Aside from very old code, you quickly learned the system. For example: http://bitsavers.informatik.uni-stuttgart.de/pdf/cdc/cyber/nos/NOS_COMPASS_… You develop a disciplined style and you never forget it. --Chuck