Modal? For IBM it was 15 bits, but for GE and UNIVAC it was 18 bits. For Burroughs it was a a 15-bit real address on the B5000 line and 18 bits on the B6500 line, but with a much larger address space. For CDC it was either 15 bits, 15 bits with a 3 bit bank number or 18 bits, depending on the processor.
There's a similar degree of variability for memory size, but 256 KiW was a typical limit outside of IBM. -- Shmuel (Seymour J.) Metz http://mason.gmu.edu/~smetz3 ________________________________________ From: IBM Mainframe Assembler List <[email protected]> on behalf of Paul Gilmartin <[email protected]> Sent: Monday, December 4, 2017 6:22 PM To: [email protected] Subject: Re: Access registers On 2017-12-04, at 15:55:20, Charles Mills wrote: > I believe someone (Harlan Mills? Fred Brooks?) said that he felt the only (or > most significant?) *error* in the System 360 design was the 24- rather than > 31- or 32-bit addressing. > Gordon Bell?: http://gordonbell.azurewebsites.net/computing%20versus%20corporate%20platforms%20011204.ppt > Anyone who has wrestled with legacy control blocks in the modern era would > probably agree. > Yes. But what was modal memory size and address size across all architectures in 1965? Very few years after that, a co-worker struggling with a CDC 3600 with 15-bit address registers extended by bank (segment, AS, ...) switching snarled, "I'm an 18-bit address man!" Cost of storage for long pointers, and microcycles for carry propagation in address resolution. Brooks rejected DAT because of the cost of address resolution. Some OS/360 control blocks had to be addressed with 16-bit pointers. 20-bit addresses suffice for 640K. I've heard similar arguments that the cost of Y2K conversion was fully justified by the capital investment in data storage saved by using 2-digit years rather than 4-digit. -- gil
