Was x86 segmented address aliasing a pitfall to be avoided or an advantage...
The way 8086 and up implement segments is kind of funny. A 16-bit segment register is shifted left by 4 and then added to the address. This naturally produces a lot of possible collisions (say...
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Is this a valid 512KiB RAM configuration for an 8086 system?
I am making a custom 8086 motherboard. I've seen a lot of documentation for IBM-PC / DOS compatible motherboards (using 8088, which I am not using). I wanted to configure 512KiB of RAM from 00000h to...
View ArticleIs it possible to corrupt a Nintendo 64 save file by turning off the console...
All consoles with memory cards (including Nintendo 64) kept reminding you that it's very important to not turn off the power while it's saving, because this would corrupt the save file.But for the...
View ArticleOrigin of the rule that swap size should be 2x of the physical memory
I can trace this recommendation that swap should be twice the size of the physical memory as far back as 1989, see SunOS 4 installation manual, page 37, but I wonder if there was ever any technical...
View ArticleLast computer not to use octets / 8-bit bytes
I am old enough to remember computers that were not octet oriented. E.g. the first that I used was an ICL 4120. It had 24 bit words which were, when necessary, divided into four 6-bit characters. There...
View ArticleDid any computers use automatically-operated mechanical storage as...
From what I understand of ENIAC, it had a very large number of manually-operated rotary switches which behaved as ROM. While programming ENIAC in the early days required a plugboard, the machine was...
View ArticleWhat's the advantage of replacing DOS/4GW with DOS/32A?
IntroductionAs far as I understand, DOS/4GW was the thing that allowed most games from MS-DOS era to access beyond the 640KB conventional memory limit. (For completeness, there was also EMS and XMS,...
View ArticleWhat was the minimum amount of addressable memory? When and why did computers...
I'm watching this video, which, at 9:51, says that around the late 1980s the majority of computers were byte-addressable.So the minimum amount of data you can retrieve from RAM was 8 bits.What was the...
View ArticleHow is the parity bit in tape storage computed?
I'm watching this video and at 5:04 it says that old cassette tape store 1 byte as 7 bit of information and a leading parity bit that could tell whether a bit of information was flipped.How was that...
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Why does the FRE() function in CBM BASIC v2 return negative values?
On Commodore machines featuring CBM BASIC v2, the FRE() function to query the amount of memory available to BASIC returns a negative number when the result exceeds 32767 bytes:This quirk does not exist...
View ArticleWhy did BASIC programs tend to READ a redundant copy of DATA?
Take for example this BASIC version of ELIZA which starts out (in lines 50–170) by a number of READ loops which copy DATA (lines 1340 and following) into a handful of arrays.Isn't this rather wasteful...
View ArticleEarliest use of SECDED memory ECC
The IBM System/370 Model 145, introduced in 1970, was one of the first mainframes to use semiconductor main memory, and instead of simple memory parity, as had been common with core memory, it used...
View ArticleWhy did the NES/FC's PPU's OAM use memory that 'decays' over time?
According to the Nesdev wiki's article on the NES/FC's PPU (https://www.nesdev.org/wiki/PPU) : "while the palette is made of static memory, OAM uses dynamic memory (which will slowly decay if the PPU...
View ArticleWhere was it possible to change the value of 4? [duplicate]
I have read it in an old "hacker test" fun text, about in the middle 90s. It was about 4.Today googling refers to the idea that maybe it had been about writing into a read-only intended memory area.But...
View ArticleHow did MS-DOS utilities like 386MAX relocate drivers from lower 640 KB to...
You copy the driver code and data but how do you redirect everything that may have jumped into the old entry point?You could scan all the interrupt vectors and see if any of them pointed to that...
View ArticleWhich 8086 or 8088-based computer, probably made by Zenith, offered EMS...
During one of my early jobs, circa 1987, I wrote some stepper motor control and data acquisition software for an MS-DOS computer in Turbo Pascal. I'm trying to recall the computer model. I'm pretty...
View ArticleWhat aspect of resetting a NES explains bits of game state being preserved?
I owned a Paperboy cartridge for the NES and something odd I noticed was that the random order of houses in the game stayed the same between pressing the Reset button, but were different when turning...
View ArticleWhy did programmers keep using EMS when XMS became commonly available?
I used to spend hours trying to get all of my drivers loaded in such a way that DOS games would still run. I actually managed to get a game that claimed it could not be run with DoubleSpace because of...
View ArticleHow much trouble was it to program segmented memory (8086)? [closed]
50 years ago, segmented memory allowed short instruction words to address high memory (above 64K) by saving the high bits of the memory address in something called the segment register.Then the short...
View ArticleHow did the IBM PC handle multiple physical devices serving memory at the...
I'm trying to figure out how the IBM 5150 PC handled the case where multiple physical devices (memory chips) were mapped to the same address within the 8088's physical address space.The closest I've...
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