Largest memory peripheral for Sinclair ZX81?
Back in the early to mid 1980s, 1981-1983, I vaguely recall seeing an advert in a (I think) UK based computer periodical monthly (such as Your Computer, or Computer and Video Games), for a memory...
View ArticleDid any x86 CPU optionally trap unaligned access?
x86 CPUs have always supported unaligned load/store.Early RISC CPUs didn't. So imagine writing portable code on a 386. It seems to work fine, but how do you know you haven't accidentally misaligned...
View ArticleIs this the reason why fread/fwrite has 2 `size_t` arguments?
It just came to me that, the C standard I/O functions fread and fwrite are having 2 size_t arguments because of I guess possibly, that on some systems, there may be more memory of which whose size can...
View ArticleDid anyone use quarter-bad RAM chips?
There was a time in the early 80s when 64k RAM chips had a significant defect rate, such that half-bad ones could be obtained at a discount. Some computer manufacturers such as Sinclair and Tandy took...
View ArticleWhy did DOS-based Windows require HIMEM.SYS to boot?
My understanding is that all versions of Microsoft Windows that ran on top of DOS — that is, the lineage from Windows 1.0 up to Windows ME, even though the reliance on DOS diminished over time —...
View ArticleVAX 11/780 16MB memory board - what was the physical size?
I'm trying to get a feel for what it looked like when you designed a computer to have a lot of memory chips stuffed into it. To that end, I found this:...
View ArticleDid 486 SMP systems provide Total Store Ordering?
Cache-coherent SMP (symmetric, or shared-memory, multi processing) systems can provide various grades of memory ordering guarantees, the stronger ones being more expensive but making it easier to write...
View ArticleWere there any games/software that used memory beyond what was advertised...
Were there any games/software that used memory beyond what was advertised as available to BASIC on the machine ?On home / personal computers any time up to 1984 .Without needing to plug in any...
View ArticleWhat were wait-states, and why was it only an issue for PCs?
PC compatibles in the 1980s were often advertised as having zero, one, two, or sometimes more "wait states". Zero wait states was the best.Basically, the wait-states I am asking about are due to the...
View ArticleWhen did the PC bus start slowing access to video RAM?
The PC architecture, from the original IBM PC onward, has always been designed around the idea that video memory will be on an expansion card. This was an unusual design decision; most 80s computers...
View ArticleCould the Z80 do interference-free video as the 6502 could?
Technically this isn't just about video since it applies to any regularlyscheduled DMA¹ from a non-CPU subsystem, but video is the most commonapplication of this technique so I'll use that as the...
View ArticleWhy do old computers (PCs) perform a long memory test on every boot?
Basically any computers from the mid 90s and earlier perform a slow memory check on every single boot. The more memory there is present, the slower that process becomes, for example:...
View ArticleWhat are the minimum system requirements to run GW-BASIC?
In DOSBox 0.74, I can run GWBASIC.EXE without any problem (DOSBox reports 632 KB of free conventional memory). It is GW-BASIC's version 3.10 dated 01-07-1989 with filesize 72576 bytes. On screen it...
View ArticleCould today's flash memory be used instead of RAM in 1980s 8 bit machines?
I wonder if this is possible and could be a retro-project? (Not something I would try myself, though)The bandwidth of flash is surely faster than yesterday's 1980s RAM (?)Why? One possible interesting...
View ArticleWas it possible to write a novel on a BBC Micro 16kb/32kb memory era computer...
BBC Micro model B has 32k memory. An average book, like Mary Shelley's Frankenstein, has about 350,000 characters in it. So you'd need over 10 times the memory to load it in, plus the software to edit...
View ArticleWhat is “character memory” to which the VIC-II memory setup register refers?
I'm trying to understand how video memory worked on the Commodore64 in text mode. I see that the VIC-II has a memory setup register (at $D018) that keeps track of some of this information along with...
View ArticleIn a 48K Spectrum why are there 5 successive contended cycles in JR?
In a 48K Spectrum, the contention pattern for the JR instruction (see e.g. https://sinclair.wiki.zxnet.co.uk/wiki/Contended_memory) is:pc:4, pc+1:3, pc+1:1, pc+1:1, pc+1:1, pc+1:1, pc+1:1There is an...
View ArticleWhat happened to 1T-SRAM?
SRAM cells take 6 transistors per bit. A long time ago, a company called Mosys claimed they could replace this with just 1 transistor, also claiming it was as fast as true SRAM. Not only that, but...
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...
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...
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