Hot answers tagged

99 votes
Accepted

Why is EEPROM called ROM if it can be written to?

Look at the development: ROM = read-only memory = can only be read when on the board, programmed in the chip factory. PROM = programmable read-only memory = can be programmed with a special programmer,...
dirkt's user avatar
  • 27k
53 votes
Accepted

Why was it common to reference memory locations using negative numbers on some BASICs?

The difference between Applesoft BASIC and the other Microsoft 6502 BASIC derivatives can be explained by the fact that Applesoft BASIC was not the first BASIC for the Apple II; the first was Apple II ...
TeaRex's user avatar
  • 1,205
49 votes
Accepted

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

Unlike its main rival the Z80, the 6502 had a size limit of 256 bytes for the hardware stack. The 6502 stack is mainly meant as a return stack and for register preservation - which usually isn't a ...
Raffzahn's user avatar
  • 218k
48 votes
Accepted

Did any notable product use Intel's first RAM?

It might be important to know that the 3101 was neither a genuine Intel development, nor intended as a RAM - at least not in a way we see RAM today. After all, what use could there be in 1970 for a ...
Raffzahn's user avatar
  • 218k
47 votes
Accepted

When did computers stop checking memory on boot?

When did computers stop checking memory on boot? Never. I remember my old 8088 used to do this (640K OK) but can't remember seeing anything like this since. Does this still happen and it's just ...
Raffzahn's user avatar
  • 218k
45 votes
Accepted

Why was computer memory so expensive and scarce?

As noted in some initial comments (but I feel fine answering, as I had the exact same ideas when I read the question), this is a general progression of technology but there are two very specific ...
manassehkatz-Moving 2 Codidact's user avatar
44 votes

Was it possible to write a novel on a BBC Micro 16kb/32kb memory era computer without expansions?

You just made a file for each chapter, like sensible people do with current word processing! It is very unusual to write something lengthy in a single document.
Brian Tompsett - 汤莱恩's user avatar
44 votes
Accepted

Could a Z80 address a total of 128 KB of ROM and RAM?

The Z80 has an address space of 64KB. That means it can perform 8 bit reads or writes to 65,536 distinct locations as specified by the 16 address pins on the CPU. As far as the Z80 is concerned that's ...
David's user avatar
  • 1,919
43 votes

How did early laser printers get by with so little memory?

To print an area of 7.5 by 10 inches at 300 DPI requires 844K if it's kept as a single bitmapped image. Does it? Maybe. Then again one cold think of many simple ways (like RLL) to compress a rendered ...
Raffzahn's user avatar
  • 218k
43 votes
Accepted

Why did Nintendo 64 (1996) memory cards require a battery inside them to retain data whereas the PlayStation (1994) ones did not?

Most likely different acrchitecture comes from idea how memory cards will/should be used and what are the available interfaces to access them. The PS memory cards do have flash memory, but the bus to ...
Justme's user avatar
  • 30.4k
40 votes
Accepted

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

The method depends on whether you have the address space or not, regardless of the RAM limitation. If you already have a 32-bit address space, but simply not much RAM, then the answer is virtual ...
Erik Eidt's user avatar
  • 3,347
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
  • 1,012
37 votes

Why did DOS-based Windows require HIMEM.SYS to boot?

Windows in protected mode requires an XMS driver — HIMEM.SYS is the one provided by Microsoft, but others can be used¹ (and the Windows Me kernel includes its own XMS driver). The role of the XMS ...
Stephen Kitt's user avatar
36 votes
Accepted

How did the ZX80 store both a useful program and screen memory?

Both the ZX80 and the ZX81 had a variable-size display file (DFILE). They didn't store the complete screen contents, but rather only the characters per line up to a terminating newline. This ...
tofro's user avatar
  • 34k
35 votes
Accepted

Last computer not to use octets / 8-bit bytes

In the early 1990's CDC sold a line of Cyber 180 mainframes. These machines were descendants of the CDC 6600 and supported that machine's 60-bit word size and 6-bit characters. Notably, one of the ...
mschaef's user avatar
  • 4,806
35 votes

What is a dropfile?

TL;DR; Dropfiles are somewhat related to virtualization as they allow to remove a process complete from execution and restart it later. Agent_L describes it quite head on as 'per-process hibernation'. ...
Raffzahn's user avatar
  • 218k
34 votes
Accepted

How did the X-Men game for Sega Genesis have its state survive a console reset?

The reset button should clear the console's memory. No, it shouldn’t. The 68000 reset vector is the first eight bytes in cartridge ROM. The cartridge will point at its own initialization code; the ...
Jacob Krall's user avatar
  • 2,309
32 votes
Accepted

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

Why are they doing that? The most important reason is that IBM introduced that check as part of the BIOS startup code, so everyone copied it to be compatible. The PC did differ from many other ...
Raffzahn's user avatar
  • 218k
31 votes

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

The basic answer is “yes”, assuming you want to be a good DOS citizen, however in many cases you don’t need to worry about it because the operating system takes care of it for you. If you’re talking ...
Stephen Kitt's user avatar
31 votes

Why is EEPROM called ROM if it can be written to?

EEPROM can't be "written to." It can be programmed. Programming is different. When there's EEPROM in a CPU's physical address space, ordinary write cycles will not affect it. Something out ...
Solomon Slow's user avatar
  • 2,089
30 votes
Accepted

Was it possible to write a novel on a BBC Micro 16kb/32kb memory era computer without expansions?

It was common to install word processing software as a ROM into one of the spare "sideways ROM" sockets on the BBC Micro, in the same way as the DFS ROM needed to operate a floppy drive. ...
Chromatix's user avatar
  • 16.8k
30 votes
Accepted

How did old computers address far more than 64K of memory despite only having a 16 bit address bus?

I don't know details of the Sharp PC-G830 specifically but the technique used to address more than 64K with a 16-bit address bus is called "bank switching". This involves setting up some ...
jwh20's user avatar
  • 3,029
30 votes

Status of brute forcing all possible memory states of a video game

An analysis such as you describe has been performed for the Activision game "Dragster" for the Atari 2600. The game polls controller inputs once per frame, and a spreadsheet has been ...
supercat's user avatar
  • 35.7k
29 votes

68000 and memory access speed

If you look at the datasheet of a typical DRAM chip of this era, say the Mostek 4116, it indeed has a cycle time of 375ns, so you can't access it at more than 2.6 MHz. But don't confuse the clock ...
dirkt's user avatar
  • 27k
29 votes

Core Memory Stability

Caveat: I can only tell about mainframes. Minis might have used different protection and handling schemes (and for sure smaller memory sizes). My detailed knowledge is based on memory up to the mid-...
Raffzahn's user avatar
  • 218k
29 votes
Accepted

Why did the Cray-1 have 8 parity bits per word?

There were 64 data bits and 8 check bits. It seems to me by the nature of parity, it should suffice to have one bit of overhead per word, rather than eight. [...] What you refer to here is a simple ...
Raffzahn's user avatar
  • 218k
29 votes
Accepted

How does the Gameboy's memory bank switching work?

ROM and RAM bank switching is controlled by a memory bank controller present on the cartridge. By writing values to areas of read-only memory, a game or program is able to specify which ROM banks to ...
b13rg's user avatar
  • 406
28 votes

Last computer not to use octets / 8-bit bytes

Unisys continued shipping 36-bit systems far more recently than 1997. The last new 36-bit Dorado - the 800 series -- was released in 2011, and superseded - per my recollection - by the Xeon-based, ...
Lexi's user avatar
  • 381
28 votes
Accepted

Which CPUs, if any, had an 8-bit address space?

PIC: 7 bit address space The Microchip PIC family of CPUs specifically the 10, 12 and 16 series have 7 bits of address space. While 7 bits is not exactly 8 bits this shows that there are commercial ...
slebetman's user avatar
  • 420

Only top scored, non community-wiki answers of a minimum length are eligible