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40 votes

Did any x86 CPU optionally trap unaligned access?

Not on a 386, but all x86 processors from the 486 forward support an alignment checking mode, which does basically what you describe: it causes an exception on any unaligned access from ring 3. See ...
user24811's user avatar
  • 1,617
26 votes
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Did 486 SMP systems provide Total Store Ordering?

BRIEF: most i486 multi-processors were probably TSO. But system vendors could definitely build non-TSO systems, and were definitely considering doing so. ---+ DETAIL ---++ SMP Marketplace ~1991 (not ...
Krazy Glew's user avatar
24 votes
Accepted

Did any x86 CPU optionally trap unaligned access?

x86 features The AC flag in EFLAGS enables alignment checking. (486 and later). The OS has to enable it by setting the AM bit in CR0. The Linux kernel for example does do that. (But GNU/Linux ...
Peter Cordes's user avatar
  • 3,197
24 votes
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When did the PC bus start slowing access to video RAM?

This question starts with a number of misconceptions about early video, memory and bus systems that need to be addressed in order to clarify what this question really appears to be about. If you want ...
cjs's user avatar
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19 votes
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How did the Fairchild Channel F provide a 2K frame buffer?

ChannelF uses 4 MK4096 4k * 1bit chips (4 middle-left rectangles in the schematics). The framebuffer is write-only, the CPU cannot directly access it through memory accesses. The CPU has no address ...
Grabul's user avatar
  • 3,647
18 votes

Did 486 SMP systems provide Total Store Ordering?

The first standard for x86-based multi-processing systems was Intel’s MultiProcessor Specification, first published in 1994 – so there weren’t really any “typical” 486 SMP systems before then. (There ...
Stephen Kitt's user avatar
16 votes
Accepted

What did it cost the 8086 to support unaligned access?

The Missing Angle It feels a bit like the question misses the most important point about the whole 8086 project over discussing implementation details: 8080/85 compatibility The 8086 was intended as a ...
Raffzahn's user avatar
  • 224k
15 votes

When did the PC bus start slowing access to video RAM?

TL;DR: When the CPU-bus became faster than the I/O-bus Now, there are always going to be wait states during active scan line, because the video chip is using some of the video memory bandwidth for ...
Raffzahn's user avatar
  • 224k
12 votes

How did the IBM 360 detect memory errors?

Usage The /360 Family uses parity all over the system, not just for memory: One Bit per Byte on main memory local storage (*1) data path address path channel data One Bit per Nibble on BCD data ...
Raffzahn's user avatar
  • 224k
11 votes

When did the PC bus start slowing access to video RAM?

The original CGA always imposed wait states on display memory accesses. The card's memory subsystem always performs one access every four pixel clocks, and only half of those are available to the CPU ...
supercat's user avatar
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11 votes
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What are the minimum system requirements to run GW-BASIC?

One thing you may want to look at. I remember encountering a bug in one of the Borland products in that they complained of being out of memory on a 640K, himem-aware, DOS 6.22 system. That was due to ...
paxdiablo's user avatar
  • 4,877
10 votes

How did the Fairchild Channel F provide a 2K frame buffer?

The Fairchild Channel F, released in 1976, was the first modern game console Let's restrict that to first successful in large numbers. Looking at the specifications, the thing that jumps out at me ...
Raffzahn's user avatar
  • 224k
10 votes

How did the Fairchild Channel F provide a 2K frame buffer?

There were two main kinds of memory chips in 1976: dynamic RAM and static RAM. A static RAM used two active transistors and two passive pullups to hold each bit, plus two more active transistors to ...
supercat's user avatar
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10 votes
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Did any 8-bit computers use 16kx4 RAM chips?

Quite a lot - well, not many different, as those chips came at a time when computers with only 16 KiB as base memory - and that's where 4416 would have been a cost saver - were already on the way out. ...
Raffzahn's user avatar
  • 224k
9 votes

What are the minimum system requirements to run GW-BASIC?

There is no single GW-BASIC. Each OEM could customize portions of it to fit its own custom hardware. For example, I had an Epson computer with a 640x400 all-pixel-addressable video adapter on the ...
Euro Micelli's user avatar
  • 2,775
8 votes
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How did the IBM 360 detect memory errors?

The IBM 360 manual Principles of operation says: The system transmits information between main storage and the CPU in units of eight bits, or a multiple of eight bits at a time. [...] A ninth bit, ...
dirkt's user avatar
  • 27.9k
8 votes

What is the motherboard part number for the Macintosh IIci that required parity memory?

661-0532 Logic Board Mac IIci 661-0583 Logic Board Mac IIci Parity from myoldmac.net - Apple Computer Model Part Numbers, confirmed in Apple's own Apple Module Identification, June 1994, pages xx and ...
scruss's user avatar
  • 21.7k
8 votes
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Simple doubling of ZX80 RAM

Prelude Given only the lower ten address lines are delivered to the RAM chips, this has the effect of duplicating the 1K RAM at every 1K boundary in those ranges Yes, that's exactly as the ZX80 ...
Raffzahn's user avatar
  • 224k
8 votes

What are the minimum system requirements to run GW-BASIC?

On screen it shows: GW-BASIC 3.10 (C) Copyright Microsoft 1983,1986 61934 Bytes free Looks quite fine to me. Whenever I try to launch the program in one true DOS 6.20, so without the use of any ...
Raffzahn's user avatar
  • 224k
7 votes
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Did the Vic-20 save money using static RAM?

Interfacing static RAM and ROM to an 6502-type processor is "nearly free". You just wire address and data lines directly, the address decoding circuit is simple. Nothing else is needed. On ...
Michael Karcher's user avatar
7 votes

Was it possible to give an Atari 800 (not XL) 64KB of RAM?

TL;DR: NO. Memory structure of the original 400/800 was based on 8 KiB chunks managed by 8 select lines, S0..S7: Sel Addr Usage S0 $0000..$1FFF 8 KiB RAM S1 $2000..$3FFF 8 KiB RAM S2 $4000..$5FFF ...
Raffzahn's user avatar
  • 224k
6 votes
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Was it possible to give an Atari 800 (not XL) 64KB of RAM?

It seems worth addressing the question in your title, Was it possible to give an Atari 800 (not XL) 64KB of RAM? Technically, it is possible to give a plain Atari 800 64KiB of RAM, and in fact quite ...
Stephen Kitt's user avatar
6 votes

Did anyone ever run out of stack space on the 6502?

Final Fantasy is a curious example. It has a spell called WARP which takes you one step closer to the entrance of the dungeon (or out of the dungeon if you're at the entrance). To implement this, the ...
Kef Schecter's user avatar
5 votes

VAX 11/780 16MB memory board - what was the physical size?

This is a VAX module but likely for an 11/780 successor, not an 11/780. The edge connector with approximately 150 signals per side and the ECL flip flops with 1987 date codes suggest that we are ...
Eli Rosenberg's user avatar
5 votes

When did the PC bus start slowing access to video RAM?

Actually, if you carefully read the BIOS for the IBM PC and CGA video (I did), you will find that (at least in text mode) it delayed every access to the video memory until the display entered a ...
David G.'s user avatar
  • 151
4 votes

Largest memory peripheral for Sinclair ZX81?

I am not 100% convinced that this is the device that I saw - it certainly isn't the same advert that I saw (as it does not have a photo of the expansion board, nor the 128 KB board). The company's ...
Greenonline's user avatar
  • 4,386
3 votes

Simple doubling of ZX80 RAM

A small addition to Raffazahn's excellent answer: take a look at the circuit diagram for the ZX80 you linked. The logic for generating the RAM CS line is here: Note, specifically, the existance of ...
occipita's user avatar
  • 2,367
3 votes

VAX 11/780 16MB memory board - what was the physical size?

Other responders have already given the exact size from data sheets, but it's also possible to get a good estimate of the size of a thing from the size of its parts. This is a useful skill when we ...
pndc's user avatar
  • 11.4k
3 votes

Why do old computers (PCs) perform a long memory test on every boot?

The PC's POST tests routines are an inheritance from the Datamaster's PID 1200 routine (see it here in action), which is an exhaustive test of all the system and allows detection and test of ROMs, RAM ...
Borg Drone's user avatar
3 votes

Could the Apple IIGS play any and all Amiga MOD files?

There is a newer version of NinjaTracker (NinjaTracker Plus) that supports almost all of the (traditional) MOD effects and supports streaming of instrument samples. It should be noted that ...
JCC's user avatar
  • 31

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