Stack Exchange Network

Stack Exchange network consists of 174 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Visit Stack Exchange
Join us in building a kind, collaborative learning community via our updated Code of Conduct.

For questions about computer memory in a retrocomputing context

6
votes
4answers
372 views

Early Basic memory management

Can anyone verify or correct my memory here? Long ago, I had access to a Commodore PET which I think had 8kB of memory. Also slightly less long ago, I had a Commodore 64 with its "elephatine" 64kB. ...
4
votes
1answer
312 views

Fastest way to write 0x00 to a zero-page memory location? (6502, Atari 2600)

I have a kernel in my 6502 game that writes two dots to a sprite, so for example: ........ ........ .XX..XX. .XX..XX. ........ ........ Either 0, 1, or 2 dots can be on at a time. This is done one ...
2
votes
3answers
225 views

What home computer was the first to use a external ROM cartridge?

When was the external ROM cartridge first used and what home computer was the first to use it?
8
votes
4answers
446 views

Columns of text in early microcomputers

As discussed in some previous questions here, 80-column text was established by IBM as the standard for business computing as early as the sixties, but monitors capable of displaying that resolution ...
4
votes
1answer
251 views

Is there any reason to chose ES, FS, or GS over the others in real mode?

The Wikipedia page on X86 Memory Segmentation says In real mode, the registers CS, DS, SS, and ES point to the currently used program code segment (CS), the current data segment (DS), the current ...
10
votes
6answers
519 views

Was photographic film ever used for data storage?

I was thinking about how Williams Tubes worked and how one could hypothetically "snapshot" (quite literally!) the state of a computer's memory by simply taking a photograph of the phosphor end of a ...
5
votes
1answer
234 views

Repurposing the parity bit

The Nintendo 64 used RAMBUS memory, width 9 bits including parity; the latter would seem unnecessary for a console, but the machine actually uses it to store an extra bit of data. This is an unusual ...
24
votes
7answers
10k views

How can you run a program that is bigger than RAM?

Suppose you have a program that is 218 words long. However you are using a 16 bit machine and have 216 words of RAM. (The RAM is directly addressed by the CPU). On the other hand, you have unlimited '...
5
votes
1answer
145 views

What kind of SIMMs can 286 PCs use?

I have a 286 Board (Octek Fox II 286) which takes up to four 30 pin SIMM modules. The manual however (http://www.minuszerodegrees.net/manuals/Octek%20-%20FOX-II%20286%20(12_16%20MHz%20versions).pdf) ...
9
votes
2answers
930 views

Unused RAM Chips on x86 machines

On classic x86 machines the upper 384 KB of system memory contains video RAM and BIOS ROM Besides other things. Those areas overlay over conventional RAM, so that you can't use all upper memory, but ...
5
votes
2answers
437 views

Is there really 1MiB of physical memory in the motherboard of a PC AT/XT?

This is a question that has been puzzling me for a while. What happens with devices like graphic cards that have their own memory chips? Do these cards read/write from their own internal memory to/...
2
votes
3answers
253 views

TSRs at top of memory conflicting with COMMAND.COM

I've seen that many TSRs installs themselves at the top of conventional memory. To do so they rely on the value at 0:413h/int 12h to tell how much conventional memory is available, and then update ...
8
votes
2answers
345 views

Is all 100% of a 64k Apple II memory usable?

Are there any areas of the 64k RAM which are permanently unusable by anything, whether by the built-in monitor ROM or user programs? Looking at $C000-C0FF, this is the "softswitch" area, and as far ...
4
votes
3answers
520 views

Amiga memory bandwidth

Looking at a timing diagram for the various kinds of memory access occurring on the Amiga http://amigadev.elowar.com/read/ADCD_2.1/Hardware_Manual_guide/node02D4.html it seems to be saying that video ...
7
votes
4answers
442 views

How did DOS know where to load itself in upper memory?

If I remember correctly, you could ask DOS to load in upper memory by writing something like... DOS=UMB ...somewhere in the CONFIG.SYS file. But the question is, how did DOS know what portions of ...
4
votes
2answers
130 views

Can fast page mode depend on the first data retrieved?

As early as the seventies, some computers used RAM in page mode, in which you can read two or more words from sequential locations in rapid succession by only supplying the column address once, and ...
21
votes
2answers
3k views

What happened to bubble memory - is it still being sold?

At one time bubble memory was advertised as being able to store huge amounts of data in the size of a sugar cube. I don't remember what the memory density was compared to today's SD cards. What ...
7
votes
1answer
160 views

In what ways is DRAM likely to fail?

A ZX Spectrum is likely to lose the same bit of every memory address if a single DRAM chip fails completely. However, if a DRAM chip partially fails, this could cause... interesting issues, ...
16
votes
2answers
2k views

What is causing the problem with the RAM in this (claimed) Spectrum 48k?

I bought what was claimed by the seller to be an Issue 4S Spectrum 48k. I tried loading games and some worked while others didn't. Turns out it was the 16k ones that worked and 48k didn't. This ...
4
votes
1answer
336 views

How does the SAM Coupé refresh its RAM?

The SAM Coupé was a ZX Spectrum compatible computer with a 6MHz Z80, 256K RAM minimum, enhanced graphics and sound and an improved BASIC amongst other features. My question is about its memory. The ...
5
votes
2answers
615 views

When did CPUs start using page mode DRAM?

According to https://en.wikipedia.org/wiki/Dynamic_random-access_memory#Page_mode_DRAM Page mode DRAM is a minor modification to the first-generation DRAM IC interface which improved the ...
14
votes
5answers
4k views

Can a 16K computer be upgraded to 64K?

A slightly odd question, but is it possible to take an old 16K computer that wasn't designed for memory upgrades, such as a Commodore 16 or PET 4016, and upgrade it to 64K as a hardware hack? I'm not ...
6
votes
1answer
230 views

What does “Expanded Memory” mean on a Philips Videopac G7000 game?

I bought a Philips Videopac G7000 because it looks awesome. Now I need to shop for some games. I'm interested in this AAA+ title, Crazy Chase: However, on the box it says EXPANDED MEMORY/MEMOIRE ...
15
votes
3answers
3k views

Do you need to allocate memory before you use it in MS-DOS?

In modern operating systems (for example: Windows), you can't access a memory location before you allocate that memory location to your program (or else a segmentation fault will occur). I am ...
5
votes
1answer
253 views

Cost differential between 2 and 4 MHz RAM chips in 1982

The most common speed of the 6502 was 1 MHz, allowing the use of 2 MHz RAM chips (half the bandwidth went to the video chip to refresh the screen). In 1982, the BBC Micro shipped, with double speeds ...
10
votes
5answers
832 views

Z80 and video chip contending for random access

Back in the 8-bit days, I used 6502 computers, where the story about memory access was easy to understand. RAM chips of the late seventies and early eighties could do 2 MHz (or a bit more e.g. 2.6 in ...
4
votes
4answers
385 views

RAM contention and what counts as different banks

From https://en.wikipedia.org/wiki/ZX_Spectrum_Contended_Memory "Contended memory space, on the other hand, is shared between the ULA and the Z80 and the ULA has higher priority. Contended memory ...
3
votes
1answer
277 views

What was the first commercially available computer with ECC memory?

In the early days of computing, memory error detection and correction was either non-existent (Wikipedia tells of Seymour Cray famously saying "parity is for farmers" when asked why he left it out of ...
3
votes
2answers
400 views

How does the Apple II address more than 128KB of RAM?

For the Apple //e, it was very common to have an extended 80-column card installed which brought the machine up to 128KB of RAM via 2 banks of 64KB each. There are soft switches in the $C0xx space ...
19
votes
4answers
2k views

Core Memory Stability

How reliable was the ferrite ring core memory system? When the power went off, did all the magnetic positions of the iron rings in the program wire grid remain exactly as they were?
18
votes
5answers
3k views

80s DRAM chips: one per bit of data bus width?

As I understand it, in the eighties the typical way of handling memory was one RAM chip per bit of data bus width. Suppose you were building a 16-bit machine and you wanted to give it 32K of RAM, you ...
7
votes
2answers
482 views

When did 64K RAM become about as cheap as 16K?

In the days of 8-bit computers, two of the more common memory configurations were 16K and 64K, implemented as eight RAM chips of 16kbit or 64kbit respectively. The setup was one chip per bit over the ...
13
votes
6answers
590 views

Largest ratio between base and maximum RAM

For example, the Apple II originally shipped with a base 4K of RAM but could be expanded to 48K, so the maximum was twelve times the base. Of all the computers ever shipped, which one has had the ...
12
votes
3answers
851 views

Speed of early ROM versus RAM chips

In the late seventies, up through around 1981, the maximum access speed of off-the-shelf RAM chips was around 2.6 MHz. Did the same speed limit apply to ROM chips of the same era? If not, what would ...
11
votes
3answers
260 views

ZX80 BASIC checking free memory

Did ZX80 BASIC have a way to check how much memory you were using and how much was left? Or otherwise: if you were writing a program on a machine with the RAM expansion, was there a way to tell ...
10
votes
2answers
631 views

How did the IBM PC handle multiple physical devices serving memory at the same physical address?

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 ...
9
votes
1answer
239 views

How many bits are stored in a memory location in a PDP-11?

PDP-11 is said to be word addressable, which means every data access returns 16-bit data. Suppose I give a read request for address 100 in memory. Will it return 8 bits (LSB) from address 100 and ...
12
votes
2answers
762 views

68000 and memory access speed

On the one hand, I get the impression that memory chips around 1980 could be accessed no faster than 2 MHz. On the other hand, the 68000, introduced in 1979, had a typical clock speed of 8 MHz. How ...
12
votes
6answers
1k views

Memory-limited workloads

I'm trying to figure out whether computing workloads, particularly those related to science and engineering, have historically been limited by memory or CPU. (By the former, I mean not memory access ...
20
votes
1answer
675 views

Which computers had features added purely for tax reasons?

I was recently reading about the Amstrad CPC 472, which was a CPC 464 with an extra, unusable 8KB of RAM added to avoid Spanish import fees on computers with 64KB or less. Did any other computers have ...
20
votes
4answers
11k views

Why did Mac OS 7 perform poorly with virtual memory enabled?

A comment in another question about supervisor and user modes in the Motorola 68000 processors, claimed that "performance was abysmal" with virtual memory enabled. An InfoWorld article about System 7 ...
20
votes
3answers
3k views

Windows 98 with 2GB of RAM

I have assembled a retro-gaming PC out of an old Shuttle SN45G with a Windows 98/Windows XP dual boot. The motherboard can handle 2GB of RAM, but apparently Windows 98 can only handle 1Gb. Windows ...
14
votes
2answers
480 views

Historical price of ROM

Historical price charts for RAM are quite readily available, e.g. in the mid-seventies a ballpark figure was a penny a byte. What was the price of ROM (assuming you were getting the chips produced in ...
9
votes
1answer
255 views

Why does my Macintosh SE FDHD only see 2 of the 4 megabytes of RAM?

I have a whole bag of 30pin SIMMS so I thought I would see about upgrading the 1 MB of RAM in my Mac SE FDHD to 4 MB. The original RAM had four sticks of OKI M41256A. These SIMMs have 8 chips each. ...
16
votes
9answers
4k views

Did early assembly games use hardcoded memory locations?

In the era of C64, Apple][ GS, and SNES, did the games use hardcoded memory locations, or did they let the assembler help them (like modern assemblers)? If yes, how did they manage the memory?
14
votes
3answers
289 views

Did any computers use automatically-operated mechanical storage as electronically-read-addressable memory

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 ...
10
votes
1answer
534 views

How to identify size of a 30 pin SIMM (Atari 1040 STe)

I have recently acquired an Atari 1040 STe with 1MB of RAM. I read that you can extend its RAM with 30 pin SIMM up to 4MB. But it can be done only with 256KB or 1MB SIMM, and that 2MB, 4MB, 8MB and ...
9
votes
3answers
727 views

Why are the PPU registers on the NES mirrored?

The NES Picture Processing Unit has eight memory-mapped registers to the CPU in registers $2000 to $2007. The are incompletely decoded, so they are mirrored every 8 bytes from register $2008 to $...
4
votes
4answers
328 views

Where are the memory controllers for IBM 5150 or Altair 8800?

Wikipedia page for memory controller states that memory controllers are either part of the northbridge, or in more recent cases, integrated into the processor. But AFAIK, neither IBM 5150 nor Altair ...
1
vote
1answer
110 views

Memory timings for a 430VX mainboard

I'm trying to troubleshoot a memory-detection problem on an old Pentium MMX system with a 430VX chipset. I've got the following memory timing options in the BIOS: DRAM Precharge Wait State: 0, 1 ...