49
TL;DR: It was IBM's idea.
IBM never intended to buy any of the software they acquired for the PC - and MS never intended to supply any OS beside Xenix.
But MS (Paul Allen) soon recognized the potential business and acted accordingly.
The Long Read
IBM had no interest whatsoever in setting up a basic software development for the PC. The strategy was to ...
45
Very simple: Because there was room for an address and it improves performance a lot. Or as the manual puts it:
It is important, however, for the programmer to realize that the simplest method of programming (using sequential drum location for succeeding instructions) causes the machine to waste a large amount of time waiting and searching.
To start with,...
26
There is a clue in the name - BCD stands for "binary-coded decimal", where 4 bits are used to represent 1 decimal digit (0-9). The hexadecimal values A-F are not used in BCD.
EBCDIC is an extended version of BCDIC, and it shifts BCDIC alphanumerics, and inserts characters in some of the non-decimal positions. But there's a simple relationship to ease ...
26
The History section of the Wikipedia Virtual Memory page seems to have the details of this:
The concept of virtual memory was first developed by German physicist Fritz-Rudolf Güntsch at the Technische Universität Berlin in 1956 in his doctoral thesis, Logical Design of a Digital Computer with Multiple Asynchronous Rotating Drums and Automatic High Speed ...
25
I have not found a reference, but here's a search for OS/2 on Trend Micro's virus encyclopedia. That finds 30 entries, some of which are actual OS/2 viruses, and some of which are interesting OS/2 security vulnerabilities.
It looks as if there are five OS/2 viruses in that list, but it's unknown if any of them are multiple names for the same virus, or ...
25
The cited source from the question is the source for the English Wikipedia page as well, that claims that there are only very few known viruses for that system.
But the low amount of viruses seems to be much bigger.
Not two, but at least five viruses are well known. That's more than double.
Arelocs also known as Aep is one of a few viruses for IBM's OS/2 ...
21
My wife began work at MSFT in the downtown Bellevue office in late 1981 (approx employee #90-ish) just a couple weeks before the company's move to the highway 520 building next to the Burger King on everyone's speed-dial. She worked with Jeff Raikes and Trisha in CorpComm. Though not software developers, CorpComm people interfaced with many departments and ...
20
As pointed out by Jon Custer, part of the reason is due to the input at the time being punch cards. If holes were close together there was a risk of the card being unreadable or ripping.
In addition, this punch card from the Wikipedia article helps explain why both uppercase and lowercase end at 0x_9. The punch card only goes from 0 to 9. I don't know how A ...
18
What is the purpose of the yellow wired panels
It's the backplane, simply the wiring of the machine.
on the IBM 360 Model 20?
Not just there, but next to every mainframe was made that way. Depending on planned (and ordered) production run some would get printed boards, but usually all wiring was done as wire-wrap. The -20 was sold in quite high numbers ...
17
It appears that the CD-ROM doesn't have a valid ISO 9660 file system. ISO 9660 requires that the file names be entirely in uppercase, lower case characters in file names aren't allowed. The directory listing in your screenshot shows only file names with lowercase letters instead of only uppercase as you'd expect to see in a MS-DOS directory listing.
The ...
16
In a 100% compatible PC, NMI is used only to communicate unrecoverable errors — normally a RAM parity failure, but possibly something else, which should reveal itself via one of the system control ports, specifically you should check:
Port A:
b4: watchdog timer status;
Port B:
b6: channel check failure (i.e. a bus failure, likely a peripheral device);
b7:...
15
One alternative to the trackpoint was a trackball, either below the screen (as in the Macintosh Portable), or next to the screen (as in the Compaq LTE Lite). When the trackball was next to the screen the mouse buttons were typically on the back (you would roll the ball with your thumb, and press the buttons on the back of the screen using index and middle ...
15
It can be found in implementations of zfs such as OpenZFS, inherited from the Solaris Kernel Memory C header file:
https://github.com/openzfs/openzfs/blob/master/usr/src/uts/common/sys/kmem_impl.h line 80
#define KMEM_FREE_PATTERN 0xdeadbeefdeadbeefULL
Quote from the magic number wiki page:
"Dead beef", Famously used on IBM systems such as the RS/...
14
The 80286 has a maximum power dissipation of 3.3W and an operating range of up to 70°C. Unless you want to operate near that point, no heat sink is needed. The ICs surface is alreaady way too large.
Beyond that it falls into the same class as iluminated cables and coloured ribbons. Not needed but doesn't do harm either (if done properly).
From a historic ...
14
The IBM5291 is one of the IBM5250 series of terminals. It provides a user interface to an IBM minicomputer.
The interface will be by Synchronous Data Link Control (SDLC). The hardware being paired co-ax wire system. This enabled a number of these terminals to be daisy chained to a single port on the host minicomputer.
There are a number of modern ...
13
It seems to me that a smart terminal would need a microprocessor, so I would expect them to start showing up in the early seventies,
Not really, as discrete, specialized processors could do the job even before that.
When did they arrive on the scene?
TL;DR: Gradually between 1964 and 1971
As with every 'first' question, the answer is rather vague and ...
13
I personally have never seen the attraction of a 'portable' that weighs more than many desktop machines, but my feelings on the matter are immaterial; the fact is that the market at the time was hungry for such machines, and the Compaq sold very well.
They were the solution for people without a fixed office, or moving locations. Not the constant moving ones ...
13
The main reason for Compaq's longer-term success in the PC market, in comparison to IBM, is what is commonly referred to as the "First-mover advantage".
In the beginning of the PC market, IBM actually held a monopoly position. As we know, in a couple of years, Compaq and others would challenge this by creating legal PC BIOS clones and bringing compatible ...
13
@raffzahn describes object files, which are not executable. They need to be read into the linkage editor, which produces a load module. That is what CSV (the newer name of the component that loads modules and relocates addresses) loads, and then the operating system eventually branches to the entry point (not always the first byte).
What you are looking for ...
12
As indicated by e.g. this description of the Phoenix BIOS, possible NMI sources are
Memory parity errors
x87 Coprocessor errors
I/O card NMI (for whatever reason the I/O card decides to invoke it)
DMA bus time-out errors (AT only)
Additionally, the Programmable Interrupt Timer (PIT; 8253 or 8254) could generate an NMI using a watchdog and possibly also on ...
12
IBM's original virtual memory machine was the System/360 Model 67, released in 1965, which was a variant of the Model 65 modified to add the address translation logic necessary to add virtual memory support. So virtual memory support at least predates the System/370 by that much.
References:
http://www.bitsavers.org/pdf/ibm/360/funcChar/GA27-2719-2_360-...
11
I found the explanation in chapters 23 and 20 of Mackenzie, Charles E, Coded Character Sets, History and Development (Addison-Wesley, 1980), which was linked in a footnote to Wikipedia's ASCII article.
In the early 1960s, 7-bit ASCII was being standardized as an communication format (the last I in the name comes from "interchange"), but this does not ...
11
Yes, for the IBM 360/30 at least the 16 32-bit registers (and 4 64-bit floating-point registers) were stored in the same core memory as the main memory.
The IBM 360/30 used the IBM 2030 Processing Unit as it's CPU, and the IBM 2030 Processing Unit Field Theory of Operation manual states on the page 1-4 that "The sixteen general registers and the four ...
10
If your primary memory is not random access, in the sense that at any instant some addressed words will take longer than others to be read, then you can potentially improve performance by having each instruction specify where the next instruction is located. The programmer is then coerced to figuring out where that next instruction ought to be.
This ...
10
On the IBM PCJr, the NMI was used by the keyboard device to signal the CPU.
(Source: “The Peter Norton Programmer’s Guide to the IBM PC”, chapter 3, under “Changing Interrupt Vectors” while discussing CLI)
10
The earlier 704 also had a decrement part in the instruction, and the 7090 can emulate the 704, so one should look at the smaller instruction set of the 704 for reasons for this design decision.
As the IBM 704 manual states on page 12, there are 5 "Type A" instructions which contain both a a decrement and an address field, namely TIX, TNX, TXH, TXL, TXI (...
9
I tried to locate some Youtube videos that quickly demonstrate what a 5250 terminal screen looks like. This one is pretty good:
https://www.youtube.com/watch?v=tn9xz1SpuyE
5250 is a block mode display system. The server sends out a blob of data to the terminal, which then by itself formats text in color in a pretty way at 80 columns by 25 lines.
The ...
9
I suspect a full answer is improbable, but to offer a fragment:
He took the Macro 10 Assembler and defined macro, so we could just
type in sort of a form of 8080 code. Then he modified the DDT-10, the
symbolic debugger that was on the 10, to understand these
instructions. He then wrote a simulator to simulate these
instructions.
...
And, ...
9
In a similar vein, Algol-68R on ICL 1900 (a 24-bit machine) initialized memory to -6815700, which when displayed as text (four 6-bit characters), spelled 'F00L', as well as possessing numerous other virtues.
https://en.wikipedia.org/wiki/ALGOL_68-R#F00L
9
Yes, it WAS due to the fact that with a rotating drum memory, you wanted the next instruction to be at a location that was just about to come under the read/write heads rather than in the next sequential location, where it could take a full revolution of the drum to be able to read the instruction.
All was not lost for the programmer, however. The 650 came ...
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