Article View: alt.folklore.computers
Article #623301Re: Quantity of machine code programmers and quantity of Assembly programmers
From: Jon Elson
Date: Sat, 28 Apr 2018 19:14
Date: Sat, 28 Apr 2018 19:14
33 lines
3637 bytes
3637 bytes
hanc...@bbs.cpcn.com wrote: > On Saturday, April 28, 2018 at 5:37:31 AM UTC-4, Andy Leighton wrote: > >> Yeah but if you were familiar with 68000 assembly language then moving to >> the 8086/88 (or successors) was painful. > > Was it a problem to move from S/360 assembler to x86 assembler? Likely. The only thing old school on the 360 was it didn't implement stacks, and the OS and programming tools didn't generally push you in that direction. The 360 had a really advanced instruction set for the time it was invented, which was about 1963. A very orthogonal arrangement, no different classes of registers (most earlier machines had index registers and accumulators, and they were for entirely different purposes.) The subroutine calling convention was a little old-school, the return address was placed (by convention) in register 14. If you then called another subroutine without saving R14, you had no way back. This often led to an infinite loop. Probably more CPU time was wasted with this mistake than all others combined. The 360 had register to register operations, indexed storage to register, and storage to storage. The indexed storage form had a base register which pointed to the beginning of your memory partition, an index register, and a 12-bit offset in the instruction field. This was VERY convenient for data structure operations (like the C construct struct). The base register made it possible to have fully relocatable object programs, but once a program began to execute, it would save physical addresses (subroutine return locations and pointers to data) and so could not be moved to a different place in memory. Jon
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