57 votes
Accepted

The start of x86: Intel 8080 vs Intel 8086?

8086 was designed to make asm source porting from 8080 easy (not the other direction). It is not binary compatible with 8080, and not source-compatible either. 8080 is not an x86 CPU. 8080 is a ...
Peter Cordes's user avatar
  • 3,207
42 votes
Accepted

386SX, NES and how much did data lines really cost anyway?

The situation with the 386(DX) v. 386SX is similar to the situation with the 8086 v. 8088. The big issue isn’t the data lines (although they do have an impact on complexity and cost when routing a ...
Stephen Kitt's user avatar
37 votes
Accepted

How much RAM could one put in a typical 80386 setup?

I very much doubt that anyone would ever have seriously considered fitting 4 GiB in a 386-based system, let alone designing such a beast. (To put this into context, I remember seeing early 1 GiB Alpha ...
Stephen Kitt's user avatar
29 votes
Accepted

What are these weird long ISA slots on this 386 board? (not VLB)

I found this page on the motherboard, which says they are some sort of "32-bit external memory card." What are these slots? They are exactly that, memory expansion. This is a rather early ...
Raffzahn's user avatar
  • 223k
29 votes
Accepted

How can a 32-bit x86 CPU start with reset vector 0xFFFFFFF0 even though it starts in 16-bit real mode?

When x86 boots, it's not strictly in classic real mode, it's in "unreal" mode, with CS.base = 0xFFFF0000 and CS.limit = 64K. On 286 and later, memory addressing doesn't use the segment ...
Peter Cordes's user avatar
  • 3,207
28 votes
Accepted

How were the test registers used on the i386 and the i486?

The 486 test registers are described in the i486 Processor Programmer’s Reference Manual, starting on page 10-8. The 386 test registers are a subset. Registers TR6 and TR7 provide access to the TLB. ...
Stephen Kitt's user avatar
25 votes

The start of x86: Intel 8080 vs Intel 8086?

To supplement @PeterCordes's excellent answer, I thought it would be worth going into the details of exactly how close to source code compatible the two processors are -- for example, how easy would ...
Jules's user avatar
  • 12.9k
24 votes

How much RAM could one put in a typical 80386 setup?

We can see the datasheet of the 386DX here. The most important part is its pinout. We have address lines from A2 to A31. It means, that yes, it could have handled 4GB memory on a motherboard. ...
peterh's user avatar
  • 1,779
24 votes
Accepted

When did the 386 overtake the 286?

According to Dataquest’s 1992 “Microcomponents Worldwide” report, shipments of 386 CPUs overtook shipments of 286 CPUs in 1991; in thousands of units shipped: Processor 1990 1991 88/86 Subtotal 21,...
Stephen Kitt's user avatar
22 votes

386SX, NES and how much did data lines really cost anyway?

So that indicates extra data lines were very expensive; the difference between a 386SX and 386DX computer came to hundreds of dollars. Not really. Sure, they need to have some room and routing - and ...
Raffzahn's user avatar
  • 223k
20 votes

Connect Ethernet via Parallel or Serial in old laptop

Yes. For example, the Xircom PE3-10BT is a parallel port adapter that allows an RJ45 connector be plugged into it. You don't get full 10 Mbps with it, but it works. Mine is powered via a PS/2 port ...
Tim Locke's user avatar
  • 4,811
20 votes
Accepted

How did AMD's 386 and 486 perform like Intel's newer generation?

The Am386 and Am486 were designed as clock-for-clock equivalents of the corresponding Intel CPUs, based on reverse-engineering and AMD’s previous second-source licenses — at least the Am386 even used ...
Stephen Kitt's user avatar
19 votes

Why did Steve Jobs choose the Motorola 68030@25 MHz for the first NeXT Computer in 1988 and not an Intel 80386DX@25 MHz processor?

As far as I can tell almost nobody except the PC makers used x86. 68k was the more common architecture by far being in the Sharp 68k, Amiga, Macintosh, Megadrive, Sun-1, Vaxstation 100, and SGI Iris. ...
davolfman's user avatar
  • 663
17 votes
Accepted

Intel 386 multiply bug

Software can identify those early steppings on the 386 by checking whether the XBTS and/or IBTS instruction can be executed, since these instructions were dropped in later chip revisions. Software ...
tofro's user avatar
  • 35k
17 votes

Identifying motherboard and CPU

I inquired about the CPU over on ee.se. The chip appears to be an AMD Am386DX-25. Compare the lower printed number (107M7NX and 107M7NZ), the fonts used, the logo at the bottom-right, and the laser-...
Alex Hajnal's user avatar
  • 9,350
17 votes

How can a 32-bit x86 CPU start with reset vector 0xFFFFFFF0 even though it starts in 16-bit real mode?

To understand this, you need to understand the basics of segment:offset addressing in protected mode: the segment value points to a descriptor, which contains a base address, segment limit and various ...
Stephen Kitt's user avatar
17 votes
Accepted

oldest free assembler targeting the 386 CPU

The Netwide Assembler (NASM) was first released in October 1996. From the beginning it supported Intel syntax (similar to MASM and TASM) and most if not all known x86 instructions, and could be used ...
Stephen Kitt's user avatar
16 votes
Accepted

Is solder-on memory upgrade an option here and how to check it

The daughterboard is the graphics card. The GD610/GD620 is a quite common chipset for LCD/VGA graphics in laptops. It uses two 64k x 16Bit RAM chips to obtain 64k x 32Bit, which is the usual VGA ...
Michael Karcher's user avatar
16 votes

How do I best simulate a 80386?

I don’t know about “best”, but Bochs includes a good debugger; here’s its most basic UI: Other UI variants exist. Note that Bochs emulates a Pentium MMX or later; it can’t be configured to ...
Stephen Kitt's user avatar
16 votes
Accepted

Why did Steve Jobs choose the Motorola 68030@25 MHz for the first NeXT Computer in 1988 and not an Intel 80386DX@25 MHz processor?

Very likely, familiarity with the Motorola environment and Motorola as a supplier within the development staff might have been technical reasons for choosing that CPU. After all, quite some of the ...
tofro's user avatar
  • 35k
15 votes

386SX, NES and how much did data lines really cost anyway?

It's not just how many data lines, but where you have to route them. While the PPU on the NES does have its own independent RAM, it is connected only to the PPU. To update the tile RAM from the main ...
RETRAC's user avatar
  • 13.7k
15 votes
Accepted

Pair Am386 with i387

The Intel 387 should work fine with an AMD 386DX; the latter was a direct clone of the Intel 386. The extra rows of pins are perfectly normal — see this photo for an example. (The extra pins were used ...
Stephen Kitt's user avatar
14 votes

What was the "32-bit" ISA bus (connector) extension for 80386 PCs?

No, this sound card is definitely not intended for such a slot that expands the ISA slot to 32 bits. This is a Compaq-specific sound card meant for a Compaq-specific ISA slot extension. There is no ...
Justme's user avatar
  • 32.1k
14 votes
Accepted

Does Intel Inboard 386/PC work on XT clone systems?

In the 1980s, there were dozens, if not hundreds, of companies making PC clones. Some used very careful and detailed engineering practices which systematically ensured that they would abide various ...
supercat's user avatar
  • 36.3k
13 votes

Connect Ethernet via Parallel or Serial in old laptop

If you have another computer to hook it up to and act as a bridge (or router), you could in principle run SLIP or PPP over the serial port to another machine. You're unlikely to get speeds exceeding ...
Vatine's user avatar
  • 681
13 votes

Identifying motherboard and CPU

Apart from the unrecognized branding on the CPU (ceramic; upper-right in photo) chip, this appears to be a bog standard ISA '386 motherboard, probably running at 25 MHz. CPU looks like the right ...
Brian H's user avatar
  • 60.8k
13 votes
Accepted

What 386-specific features did Linux use?

One of Linus’ other posts provides the answer: PS. Yes - it's free of any minix code, and it has a multi-threaded fs. It is NOT protable (uses 386 task switching etc), and it probably never will ...
Stephen Kitt's user avatar
12 votes
Accepted

What exactly were those 808X computers that would switch to 80386 upon Ctrl-Alt-Del?

What you describe sounds like the PC Elevator: The PC Elevator 386 is a coprocessor-type accelerator board. The system's native CPU remains available for any programs that are sensitive to speed or ...
snips-n-snails's user avatar
12 votes
Accepted

80387 transistor count

I’ve wondered about this for a long time — manufacturers don’t seem to communicate FPU transistor counts as readily as CPU counts. The best I’ve found so far is a claim on coprocessor.info that the ...
Stephen Kitt's user avatar
11 votes
Accepted

What was the fastest third party FPU?

I don’t recall SPARC systems having separate sockets for discrete FPUs; in particular, the Weitek SPARC POWER µP was a replacement SPARC CPU which derived much of its speed benefit from doubling its ...
Stephen Kitt's user avatar

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