From mboxrd@z Thu Jan 1 00:00:00 1970 From: peter@rulingia.com (Peter Jeremy) Date: Sat, 20 Oct 2012 09:13:14 +1100 Subject: [TUHS] Bryan Cantrill on bfs & ta In-Reply-To: <20121019205428.GD6410@mercury.ccil.org> References: <508087E8.7030309@gmail.com> <20121018234041.GB96785@eureka.lemis.com> <20121019205428.GD6410@mercury.ccil.org> Message-ID: <20121019221314.GR33428@server.rulingia.com> On 2012-Oct-19 15:44:27 -0500, Clem Cole wrote: >the 68000 and 68010 were 16 bit internals. It depends whether you are talking implementation or architecture. The M68000 architecture was basically 32 bits (Motorola initially skimped on the multiply & divide instructions and referred to it as a "16-/32-bit architecture"), though the initial implementation used a 16-bit ALU. To go back further, the IBM System/360 was a 32-bit architecture but the low-end implementation (360/20) only had 8-bit wide memory and an 8-bit wide ALU and there was also a 16-bit wide implementation. >the external logic (ie pins) supported 24 bits of address. moto >fortunately passed all 32 bits along on the first chip and onto >storage (thank you Les & Nick) so when later versions had a full 32 >bit shifter everything just worked. They clearly defined that the programmer's view was a 32-bit address but some implementations didn't map all the address bits onto pins. Note that this approach of only physically implementing a subset of the address bus has continued into the 64-bit chips - most chips only have 36-40 physical address bits and 40-48 logical address bits. (Though one big difference is that the unimplemented address bits are validated instead of ignored). >PPS. we relived this whole argument with 64 bits and it was >interesting that we generally came to think LP64 made more sense for >chips like Alpha I think a lot of this was also driven by the large amount of software that was ILP32. Converting int from 32- to 64-bits would add a lot of pain for very little benefit. Just making code work with LP64 was painful enough. On 2012-Oct-19 16:54:28 -0400, John Cowan wrote: >Sounds like the 8088, which used an 8-bit bus but 16-bit registers >and operations. The 8088 and 68008 were basically 8086/68000 chips with reworked bus interface logic so that the external data bus was only 8-bit (and the 68008 also cut the address bus from 24- to 20-bits). Other than being slower, they appeared the same as their 16-bit cousins. They were aimed at applications where price was more important than performance: Using the 8088 meant that IBM only needed 8 64Kx1 DRAM chips and the 68008 used a much smaller and cheaper 40-pin DIP instead of the 64-pin DIP needed for the 68000. -- Peter Jeremy -------------- next part -------------- A non-text attachment was scrubbed... Name: not available Type: application/pgp-signature Size: 196 bytes Desc: not available URL: