78
votes
Accepted
Why did 1950s-60s computers have such wide words?
And if you go back further, e.g. to the ENIAC, you'll see a word size of 40 bits.
And if you go back even further, to mechanical calculators, you'll see word sizes determined by the number of decimal ...
- 25.5k
47
votes
Accepted
Why does an instruction include the address of the next instruction on the IBM 650?
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 ...
- 207k
45
votes
Why did the IBM 650 use bi-quinary?
I will just explain what a bit is. It's a binary digit. 0 is numerically zero, 1 is numerically one. If you want to add 1 and 1, in binary it overflows. the result is 0, and a carry out. As you ...
- 37.9k
30
votes
Accepted
Why did the IBM 650 use bi-quinary?
Quibbling about the right meaning of "bit" aside, some advantages of the 2-of-7 biquinary representation are:
Simpler circuits. In a quinary adder circuit, the output of each of the 5 output lines ...
21
votes
Accepted
When did the IBM 650 have a "Table lookup on Equal" instruction?
The TLE instruction is a modification of the TLU instruction.
TLU (Table LookUp) (Opcode 84) compared a word with a series of consecutive words on the drum and finished as soon as an entry was found ...
- 207k
21
votes
Why did 1950s-60s computers have such wide words?
Longer words mean more bits can be processed at once. An 8 bit processor can perform a 32 bit calculation, but it has to do it in 4 stages of 8 bits each. A 32 bit processor can do it in one stage.
...
- 15.1k
13
votes
Why did 1950s-60s computers have such wide words?
A possible answer occurs to me: it might be precisely because of the slow memory.
Say you want to add a pair of ten-digit decimal numbers, SUM += VAL, on a 6502. That chip has a BCD mode in which it ...
- 58.1k
10
votes
Why does an instruction include the address of the next instruction on the IBM 650?
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 ...
- 32.4k
9
votes
Why does an instruction include the address of the next instruction on the IBM 650?
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 ...
- 201
5
votes
Accepted
IBM 650 - how many logic gates?
How many logic gates did the IBM 650 have?
It's a rather useless question. When is a gate a gate? Is a wired-OR a gate? Does a 38-input-OR, used to create a zero condition count as much as a two-...
- 207k
5
votes
Why did the IBM 650 use bi-quinary?
Storing a one-of-two selection using vacuum tube technology doesn't require one valve (combination of an anode, cathode, and one or more grids); it requires two. Thus, holding four bits would require ...
- 33.9k
5
votes
Why did the IBM 650 use bi-quinary?
This isn't intended as an answer per se, but I want to provide some support for OmarL's explanation by quoting official documentation for the machine, which speaks of binary values as units of ...
- 3,445
3
votes
Why did 1950s-60s computers have such wide words?
I'd suggest that one issue is that a 1950/60s mainframe was considered to be a significant corporate resource, and by and large enough would be spent on it that it could serve the needs of the entire ...
- 1,997
3
votes
Why did 1950s-60s computers have such wide words?
The premise isn't entirely true. The IBM 1401, perhaps the most popular computer of the 1960's, used a seven bit word (not including the parity bit). This was a business machine, not a number cruncher....
- 1,361
1
vote
Why did 1950s-60s computers have such wide words?
The 8086 addressing wasn't 20 bits, it's actually two 16-bit components (with a 16-bit ALU); those components being a segment and offset.
It sounds like 16+16=32, but the actual location was segment*...
- 11
1
vote
Why did 1950s-60s computers have such wide words?
The early computers were created to do high precision scientific calculations that couldn't be done by hand (practically).
The newer computers you mention from the 70s and 80s where business and home ...
- 51
1
vote
Why did 1950s-60s computers have such wide words?
Many early machines processed data in bit-serial fashion, which meant that doubling the word size would reduce the number of words that could be held by a given number of memory circuits, but wouldn't ...
- 33.9k
1
vote
Why did 1950s-60s computers have such wide words?
Given the small (by today's standards) memory, it was very convenient to be able to include a full memory address within a machine instruction.
For instance, Honeywell 6000 assembler
instructions ...
- 265
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